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Printable ResourcesWho You Gonna Call? Mousebusters!

A: Pre/Post TestB: Pre/Post Test Answer KeyC: The Hook Student Worksheet D: Image Response WorksheetE: Cartoon Clips Station F: Code of Cooperation G: Career Roles H: Gravitational Forces Student HandoutI: Gravitational Forces Teacher ResourcesJ: Electrical Force and Circuit StationsK: Electromagnetic Stations L: Teacher Guide to Forces with DemonstrationsM: Teacher Resource: Mouse Trap DesignsN: Engineering Design ChallengeO: Engineering Design RubricP: Bill of MaterialsQ: Presentation DetailsR: Brief Technical Discussion of Gravitational and Electromagnetic Forces S: Testing – Data Collection SheetT: Design Scalability Worksheet

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Who You Gonna Call? Mousebusters!Appendix A: Pre/Post TestName: _____________________________________ Date: ______________ Period: _______

1. Mike has an assignment to construct a scale drawing of a trap. He plans to use the scale 1 inch = 4 inches. If the height of the trap is 16 inches, how tall should it be in the drawing?

a. 6 inchesb. 2 inchesc. 4 inchesd. 8 inches

2. Below are a list of forces. Circle the forces that act at a distance. Then give an example of how each of those forces act on an object.

a. Frictional Forceb. Gravitational Forcec. Tension Forced. Air Resistance Forcee. Magnetic Force f. Electrical Forceg. Applied Force

3. Can any object have a magnetic field? Why or why not?

4. Gravitational forces (weaken/strengthen) as distance increases.

5. Objects are surrounded by a region of influence called a ____________. a. Path b. Model c. Field d. Force

Draft: 5/17/2023

Who You Gonna Call? Mousebusters!6. When a nonzero net force acts on an object, the force

a. Changes the motion of the objectb. Must be greater than the reaction forcec. Does not change the motion of the objectd. Is equal to the weight of the object

7. Draw the electric field for a single positive charge. Be sure to show which way the field lines point. Explain what happens to the electric field and force as you move away from the charge.

8. If a square has a side length of 5 cm. What would the new area of the square be if it was increased by a scale factor of 2? How does that relate to the area of the original square?

9. Given the following linear function, explain what will happen if the x-value is 50. (2 points)

X Y1 -86 12-2 -200 -12

Draft: 5/17/2023

Who You Gonna Call? Mousebusters!10. Which of the following graphs represents the relationship between gravitational force

that two objects exert upon one another and the distance between the two objects?

Draft: 5/17/2023

Who You Gonna Call? Mousebusters!

Appendix B: Pre/Post Test Answer Key

1. Mike has an assignment to construct a scale drawing of a trap. He plans to use the scale 1 inch = 4 inches. If the height of the trap is 16 inches, how tall should it be in the drawing? (1 pt)

a. 6 inchesb. 2 inchesc. 4 inchesd. 8 inches

2. Below are a list of forces. Circle the forces that act at a distance. Then give an example of how each of those forces acting on an object. (6 points; 1 for each of the correct forces and 1 for each of the examples)

a. Frictional Forceb. Gravitational Force : Gravity pulling objects towards the center of earth, a

ball going to the floor when dropped. c. Tension Forced. Air Resistance Forcee. Magnetic Force : Compass, MRI’s f. Electrical Force: Staticg. Applied Force

3. Can any object have a magnetic field? Why or why not? (2 points)2 points- Not all objects can have a magnetic field because an object must have a charge to have a magnetic field.1 point- No0 Points- any answer that is not one above

4. Gravitational forces (weaken/strengthen) as distance increases. (1 point)

5. Objects are surrounded by a region of influence called a ____________. a. Path b. Model c. Field d. Force

6. When a nonzero net force acts on an object, the forcea. Changes the motion of the objectb. Must be greater than the reaction forcec. Does not change the motion of the objectd. Is equal to the weight of the object

Draft: 5/17/2023

Who You Gonna Call? Mousebusters!7. Draw the electric field for a single positive charge. Be sure to show which way the field

lines point. Explain what happens to the electric field and force as you move away from the charge.

The electric field will get weaker as you move away from the center charge.

8. If a square has a side length of 5 cm. What would the new area of the square be if it was increased by a scale factor of 2? How does that relate to the original square? (2 points)

2pts: The new area is 4 times as great at the original area; the new area is 100cm2

1 point: One of the above two pieces is correct; one is incorrect or missing0 points: none of the above answers

9. Given the following linear function, explain what will happen if the x-value is 50. (2 points)

X Y1 -86 12-2 -200 -122 points- Answer shows all work and explains that the x-value is 188 because the rule is 4x -121 point- Answer explains that the y-value will be larger and around 1880 point- Answer is wrong

10. Which of the following graphs represents the relationship between gravitational force that two objects exert upon one another and the distance between the two objects? A. Graph A B. Graph B C. Graph C D. Graph D

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Who You Gonna Call? Mousebusters!Appendix C: The HookName: _____________________________________ Date: ______________ Period: _______

Ricky talks about his less than fortunate encounter with a gopher and run-ins with several other animals. Ricky’s job is to study animal behavior, develop a plan to humanely trap these animals and then to remove them for his clients. As populations continue to grow, urbanization continues to put wild animals up against the humans moving into their former habitats. From bats in the attic to mice in the pantry to the occasional raccoon in the trash can, wild animals can frequently be a nuisance. Today, you will brainstorm some ideas how we can humanely remove some animals Ricky has dealt with in the past. In your group, discuss what you already know about the following animals:*Gopher, Bat, Lizard, and Snake

Ask yourself what other information you would need to know about these animals to humanly trap them.Develop a plan to humanly trap these animals. Animal What I Know… What Do I Need to

Know…What’s the Plan?

Gopher

Bat

Lizard

Snake

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Who You Gonna Call? Mousebusters!Appendix D: Image Response WorksheetName: _____________________________________ Date: ______________ Period: _______

View each of the images. Decide how the item in each image would be beneficial to use in engineering a trap. Write your response in the box to the right of the image.

Image: https://bagntell.wordpress.com/hardware/

Image: http://imgkid.com/open-picnic-basket.shtml

Image: https://grabcad.com/library/suspended-coaster-seat

Image: https://www.arcat.com/bim/crane/RevolvingDoor_BF_Crane_1000-Series-Curtain-Panel-Based.jpg

Draft: 5/17/2023

https://www.arcat.com/bim/crane/RevolvingDoor_BF_Crane_1000-Series-Curtain-Panel-Based.jpg

https://www.arcat.com/bim/crane/RevolvingDoor_BF_Crane_1000-Series-Curtain-Panel-Based.jpg

https://grabcad.com/library/suspended-coaster-seat

https://grabcad.com/library/suspended-coaster-seat

http://imgkid.com/open-picnic-basket.shtml

https://bagntell.wordpress.com/hardware/

https://bagntell.files.wordpress.com/2009/12/metal-snap-buttons-snap-fastener.jpg

Who You Gonna Call? Mousebusters!Appendix E: Cartoon Clips Student Worksheet Name: _____________________________________ Date: ______________ Period: _______

Directions: For each clip, determine what force (gravitational, magnetic, and/or electric) is used and describe the mechanism could be used as a trap. Clip #1 Clip #3

Type of Force? Type of Force?

Mechanism Used? Mechanism Used?

Clip #2 Clip #4

Type of Force? Type of Force?

Mechanism Used? Mechanism Used?

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Who You Gonna Call? Mousebusters!Appendix F: Code of Cooperation

Code of CooperationYour team’s first task is to decide how your team will cooperate throughout the design challenge. As a team, decide on your anticipated goals, or expectations, for each other and yourself. Also, decide what actions, or consequences, will occur should a team member fail to follow the team code of cooperation.

Decide on a team name.

List all members of the team next to their career position for this challenge.Project Manager: Materials Engineer: Biologist:Mechanical Engineer:

List 4-5 anticipated goals.All team members agree to:1.

2.

3.

4.

5.

When a team member lets their team down by ignoring the anticipated goals listed above, the following actions will be taken based on number of offenses.Step 1:Step 2:Step 3:

Teacher Approved:___________ (Teacher’s initials)

Team Member Signatures:

By signing this document on one of the lines below, I am stating that I agree to meet the anticipated goals and I understand the consequences if I fail to do so.______________________________ ___________________________________________________________ _____________________________

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Appendix G: Career RolesName: _____________________________________ Date:_________________ Period:____

Discuss each career with your group. Write the name of the group member completing each career in the completed by section.

Role Responsibilities

Project Manager

completed by:

Responsible for: Technical performance (trap performance) Schedule (ensure team completes tasks on

time) Budget (Bill of Materials) Presentation

Materials Engineer

completed by:

Responsible for: Survey available materials and cost Recommend materials that will work well for the

design of the trap while saving cost Obtain materials (from teacher or assign

members to supply) and keep track of how much is used

Assist in the completion of the Bill of Materials

Biologist

completed by:

Responsible for: Research animal – information that would be

needed to ensure the proper trap is constructed Recommend trap design Assist in the completion of the presentation

Mechanical Engineer

completed by:

Responsible for: Lead trap design activity Draw trap sketch Recommend force(s) for trap design

Draft: 5/17/2023

Who You Gonna Call? Mousebusters!Appendix H: Gravitational Forces Student HandoutName: _____________________________________ Date: ______________ Period: _______DemonstrationThe instructor will demonstrate what happened when a golf ball and a ping pong ball are dropped from the same height. Draw a picture to describe the demonstration and predict what will happen. Which ball will hit the ground first?

Newton’s law of gravitational force backgroundGravity (gravitational force) is a force present between two objects with mass. Every particle with mass attracts every other particle. The standard formula for the law of gravitation is:

where,

G≈6.674×10−11N (m /kg )2

In your own words describe what the symbols stand for in the formula for gravitational force

m1 = _____________________________________________

m2 = _____________________________________________

r =______________________________________________

G = _____________________________________________

Gravity governs motion throughout the universe. It is most apparent when one mass is very large, like Earth. The acceleration of an object toward the ground caused by gravity, near the surface of the Earth, is called normal gravity, or 1g. It is equal to 9.8 m/sec2. This is the rate of change of the velocity and it is constant on Earth.

Draft: 5/17/2023

http://upload.wikimedia.org/wikipedia/commons/0/0e/NewtonsLawOfUniversalGravitation.s

Who You Gonna Call? Mousebusters!Video LessonWatch the NASA video about mass vs. weight and fill-in the blanks below.http://education.ssc.nasa.gov/mvw_intro_video.asp (total time: 6mins, can be cut off at 4 mins)

is the amount of matter in an object. It is important to understand that the of an object

is not dependent on gravity. Bodies with greater are accelerated less by the same

force.

is the vertical force exerted by a mass as a result of gravity. can also be defined as

the strength of the gravitational pull on the object; that is, how heavy it is. is

dependent on gravity.

The standard formula for weight on Earth is:

W=m1×g

What are the units of weight?

What is the value and unit of the constant g?

Draft: 5/17/2023

http://education.ssc.nasa.gov/mvw_intro_video.asp

Who You Gonna Call? Mousebusters!Activity Draw an arrow to describe the direction of the instantaneous velocity of the International

Space Station (ISS). Draw an arrow beginning at the ISS towards the center of mass of the Earth. What is the direction of the force of Earth’s gravity on the ISS?

Discussion questions 1. If gravity has a downward force on the ISS why doesn’t it fall to the Earth?

2. Why did the apple fall towards the center of Earth and the onion just float on-board the ISS?

3. What would be the force of gravity at the center of the Earth?

4. Does the moon have a gravitational force exerted on the ISS?

Brainstorming exercise

How can you use the force of gravity to activate a spring-triggered mouse trap?

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Who You Gonna Call? Mousebusters!Appendix I: Gravitational Forces – Teacher ReferencesDemonstrationThe instructor will demonstrate what happened when a golf ball and a ping pong ball are dropped from the same height. Draw a picture to describe the demonstration and predict what will happen. (Which ball will hit the ground first?)

Newton’s law of gravitational force backgroundGravity (gravitational force) is a force present between two objects with mass. Every particle with mass attracts every other particle. The standard formula for the law of gravitation is:

where,

G≈6.674×10−11N (m /kg )2

In your own words describe what the symbols stand for in the formula for gravitational force

m1 = ___mass of the first object (notice: even though the mass m1looks bigger, the attractive force F1 and F2 are the same)_

m2 = __mass of the first object ___

r = _distance between the 2 center of masses_

G = _gravitational constant_

Gravity governs motion throughout the universe. It is most apparent when one mass is very large, like Earth. The acceleration of an object toward the ground caused by gravity, near the surface of the Earth, is called normal gravity, or 1g. It is equal to 9.8 m/sec2. This is the rate of change of the velocity and it is constant on Earth



The instructor can demonstrate how a mouse trap is triggered by releasing a spring. If there is time students can try using the golf ball or the ping-pong ball to trigger the mouse trap or the instructor can guide the students in a thought experiment.

Draft: 5/17/2023


Who You Gonna Call? Mousebusters!Video LessonWatch the NASA video about mass vs. weight and fill-in the blanks below.http://education.ssc.nasa.gov/mvw_intro_video.asp (total time: 6mins, can be cut off at 4 mins)

is the amount of matter in an object. It is important to understand that the of an object

is not dependent on gravity. Bodies with greater are accelerated less by the same

force.

is the vertical force exerted by a mass as a result of gravity. can also be defined as the

strength of the gravitational pull on the object; that is, how heavy it is. is dependent on gravity.

The standard formula for weight on Earth is:

W=m1×g

What are the units of weight?Mass is units of kilograms (kg), weight is a force so the MKS units are Newtons (N)

What is the value and units of the constant g?g is an acceleration, units are m/s2

Draft: 5/17/2023

http://education.ssc.nasa.gov/mvw_intro_video.asp

Who You Gonna Call? Mousebusters!Activity Draw an arrow to describe the direction of the instantaneous velocity of the International

Space Station (ISS). Draw an arrow beginning at the ISS towards the center of mass of the Earth. What is the direction of the force of Earth’s gravity on the ISS?

Discussion questions 1. If gravity has a downward force on the ISS why doesn’t it fall to the Earth?The ISS is free-falling towards Earth, at the same time it is traveling away from the Earth at a constant speed due to the force applied at its initial launch. The direction of speed of the ISS(at any instantaneous point in time) is tangent to its orbit. At the same time gravity is pulling it towards the center of the Earth. The result is that the direction of the ISS is always falling towards the center of the Earth as it attempts to move in the original direction of motion. The change in the velocity is perpendicular to the direction of the velocity.The direction of the force on an object is not necessarily the direction of its velocity, rather the direction of the force must be along the direction of thechange in velocity. Consider a car traveling at a constant speed is pushed by another car from a perpendicular direction. It doesn’t move perpendicularly, but glances off its original direction. 2. Why did the apple fall towards the center of Earth and the onion just float on-board the ISS? The apple falls towards the center of the Earth because that is the direction of the force of gravity. The onion on-board the ISS also falls towards the center of the Earth, but since the ISS is also falling at the same rate the onion appears to the astronauts to be floating. From the perspective of the Earth, the onion is not motionless. The onion and the ISS are traveling very fast in orbit around the Earth. It is correct to say that the onion is weightless, but incorrect to say that the onion has no mass. Mass is a fundamental property of matter and doesn’t change. Weight is the force due to gravity. It is incorrect to think that there is no force on the onion. The onion and the ISS both experience force due to gravity even though they are very far away from Earth. 3. Does the moon have a gravitational force exerted on the ISS?Yes. Since every mass has a force on every other mass, there exists an attractive force on the ISS due to the Earth, and there also exists a force due to the Moon. However, since the Earth is so much larger in mass and also much close to the ISS than the Moon,the attractive force of the Moon on the ISS is negligible. A note on distance: It is tempting, but incorrect to think that the microgravity experience on-board the ISS is due to the fact that gravity gets weaker with

Draft: 5/17/2023

Who You Gonna Call? Mousebusters!distance. While this it essentially true that the gravitational force felt on the ISS is weaker than it would be if it were on the surface of the Earth, this effect is less than 1%. The weightlessness is due to the free-fall effect, which is set into motion by the initial launch of the vehicle. If the ISS were to stop moving around the Earth, it would fall towards the Earth due to the effect of gravity – just like the apple falls. 4. What would be the force of gravity at the center of the Earth?Zero. Every particle that makes up the Earth has a force on every other particle due to gravity. However at the center of the Earth all of the forces (direction and magnitude) sum to cancel each other out and the net force at the center of mass is zero.



Draft: 5/17/2023


The following brief description of gravitational force is more in depth than a middle school student needs to know, but a solid foundation in this basic physical concept may allow the instructor to correct common misconceptions held by students.

Gravitational force is of the four known fundamental forces that govern how matter interacts throughout our universe. All forces act at a distance through all kinds of media (i.e., air, water, or solid materials) even when there is no material present such as the vacuum of outer space. The SI unit of all forces is the Newton (N), which is equivalent to 1kg ∙m /s2 in base units.

Gravitational force describes the force present between two objects and is proportional to the mass of the two objects and inversely proportional to the square of the distance, as

described by, f grav=Gm1m2

d2 , where m1and m2 are the mass of the two objects and d is the

distance between the them. Gis thegravitational constant, sometimes called the Newtonian constant of gravitation (G=6.673 ∙10−11N (m /kg )2). Big G is often confused for little g which is the Earth’s acceleration of an object due to gravity. Big G is a constant that explains behavior throughout the universe, and little g describes acceleration due to the Newtonian force of Earth’s gravity. On average, g≅ 9.81m /s2 on the Earth’s surface.

A free body diagram is used to describe the magnitude and direction of forces on a body. If all of the force vectors (direction and magnitude) sum to zero, the body will be in equilibrium. A common misconception is that forces cause motion. The correct concept is that forces cause acceleration which is a change in the velocity. Consider the forces of a hockey puck on a frictionless surface like ice. There is a Newtonian (gravitational) force pointed downward. This is the force on the hockey puck due to the mass of the Earth. There also exists an equal and opposite force, pointed upward, describing the force on the Earth due to the mass of the hockey puck. Even though the mass of the Earth is much bigger than the mass of the hockey puck the forces are equal, since the gravitational force depends on the mass of both objects. There is no motion due to the gravitational force in this example – yet the force still exists. The net force is zero.

Another common misconception is that motion of objects implies a force has been applied. Since these forces balance, the hockey puck does not experience acceleration. It may in fact be moving with a constant velocity. Consider a situation where the hockey puck is moving across a frictionless surface like ice. If the hockey puck changes its velocity (from stationary to moving or from moving to stationary) then there must have been a force applied, but the hockey puck could be moving with a constant velocity even if all the forces are balanced. Recall Newton’s third law of motion: objects in motion stay in motion.

Objects in free-fall are accelerating due to the gravitational force. That is, they are falling faster and faster at a rate of 9.81m /s2, independent of their mass. A third common misconception is that heavier objects (those with more mass) fall faster than lighter objects. Our common experience often includes the non-negligible effects of friction due to air resistance, leading to this incorrect belief.

By definition, weight (SI unit is N) is the gravitational force on an object in the presence of a much larger object like the earth. Mass (SI unit is kg) is often confused with weight. While mass is a fundamental property of an object, the weight of the object depends on the gravitational force field that it resides in.

References for more information:1. Physics Classroom http://www.physicsclassroom.com/ web resources and tutorials2. NASA Educational Resources:

http://www.nasa.gov/audience/foreducators/index.htmlStudent activities and videos.

http://www.nasa.gov/audience/foreducators/index.html

http://www.physicsclassroom.com/


3. Ask Rose – Homework Hotline http://www.askrose.org/ Rose-Hulman University students will offer tutoring over the phone to students to help them with homework questions

Appendix J: Electrical Force and Circuit StationsName: _____________________________________ Date: ______________ Period: _______

Instructions: Read the following and answer the questions before beginning the stations that your teacher has prepared for you.

Electrical CurrentWhen electrons move, they carry electrical energy from one place to another. This is called current electricity or an electric current. A current of electricity is a steady flow of electrons. When electrons move from one place to another, round a circuit, they carry electrical energy from place to place like marching ants carrying leaves. Instead of carrying leaves, electrons carry a tiny amount of electric charge.

A lightning bolt is one example of an electric current, although it does not last very long. Electric currents are also involved in powering all the electrical appliances that you use, from washing machines to flashlights and from telephones to MP3 players. These electric currents last much longer.

Electric currents are measured in amperes (A), or amps. The higher the number of amps, the more electrical energy in the current.

Have you heard of the terms potential energy and kinetic energy? Potential energy means energy that is stored somehow for use in the future. A car at the top of a hill has potential energy, because it has the potential (or ability) to roll down the hill in future. When it's rolling down the hill, its potential energy is gradually converted into kinetic energy (the energy something has because it's moving).

Static electricity and current electricity are like potential energy and kinetic energy. When electricity gathers in one place, it has the potential to do something in the future. Electricity stored in a battery is an example of electrical potential energy. You can use the energy in the battery to power a flashlight, for example. When you switch on a flashlight, the battery inside begins to supply electrical energy to the lamp, making it give off light. All the time the light is switched on, energy is flowing from the battery to the lamp.

The electrical current that runs from the battery to the bulb is caused by the differences in potential energy of the two locations. This is called potential difference. In batteries, this difference is caused by the positive and negative terminals. The current will flow from the positive end of the battery, through the wire and any load attached, and back into the negative end of the battery. The electric charges will always flow from a region of higher potential energy (the positive terminal) to a region of lower potential energy (the negative terminal). The potential difference of an electric current is also called voltage and is measured in units called volts (V). The higher the voltage, the bigger the difference in potential energy.

1. What is an electric current?

2. What is the unit of measurement for rate of electric current?

http://www.askrose.org/


3. Electric current flows from areas of _____________________ potential energy to area of ________________potential energy.

4. Potential difference is also called _____________ and is measured in units called ______________.

Electrical Circuit StationSupplies:

BatteryBattery ClipLight bulbWireSwitch

Procedure:Try to light the bulb by creating a circuit using only a battery, one bulb and wire. (It may take a few tries but it is possible) Make sure it is clear which end of the battery is which and exactly where you attach the wire.

SERIES CIRCUITSKETCH WHAT WORKED SKETCH WHAT DIDN’T WORK

Now take a second lightbulb and see if you can apply to what you learned above.Draw two ways that worked and two that didn’t work on the chart.

PARALLEL CIRCUITSKETCH WHAT WORKED SKETCH WHAT DIDN’T WORK


Take another piece of wire and a switch. Add the switch to your circuit and experiment to see how the switch works to open and close the circuit. In the box below sketch what your device looks like.

5. Explain why the circuits in your “did not work” column not work.

6. What was the energy source in your circuits?

7. Is a switch necessary to make a circuit work? Why or why not?

8. Why would you want to include a switch in an electric circuit?

9. Compare what happened to an electric current when it reaches an open switch and when it reaches a closed switch.

10. What do you think would happen to the current of electricity if you remove the light bulb?

ALTERNATIVE SWITCHNow that you have built your circuits watch the following YouTube video and answer the questions.https://www.youtube.com/watch?v=9YZ7KQ-g6lw

11. Sketch the design of the pressure switch be sure to label parts well, you will need this later.


Electrical Force StationSupplies:Cotton towelPlastic Produce BagScissorsBalloonProcedure:

1. Use a pair of scissors to cut a strip from the open end of the produce bag. Once this strip is cut you should have a plastic band or ring.

2. Blow up the balloon to its full size and tie off the end. 3. Rub the cotton towel over the surface of the balloon for 30-45 seconds. This transfers

negative charges from the towel to the balloon. 4. Flatten the plastic band on a hard surface and rub the towel on the band for 30-45

seconds. 5. Hold the plastic band about one foot over the balloon and release it. In the box below

sketch what is happening.

6. Experiment with your team what is the magic distance where the balloon no longer influences the fall of the plastic bag. Explain.

Both the balloon and plastic produce bag have negative charges and are repelling against each other. In the box below sketch and explain what the charges (positive/negative) are when the balloon is near someone with long hair.

Based on the two experiments above what can you infer about positive and negative charges, electrical forces and distance?


Appendix K: Electromagnetic Stations Student HandoutName:_________________________________________ Period:_____Electromagnetic Stations

1. Fill out how long it takes each object to drop through the pipes.

Object Copper Pipe (Seconds)

PVC Pipe (Seconds)

Wooden BallRubber BallMarbleMagnet

What did you notice about the different objects in the pipes? Find and record the mean, median and mode. What does this tell you about the copper pipe and PVC pipe?

Station 1: Fill out the chart below with measurements from the voltage and light output.Type of Battery Voltage Light OutputAAAAACD9V

Find the mean, median and mode of the voltage and the light output. What could be influencing your results? What measure of center would be appropriate to display this data? Why?

Station 2:In this station you will measure the distance it takes a paperclip to be moved by the electromagnet provided and graph your results.Number of Coils

Distance (try 1) Distance (try 2) Distance (try 3)

1050100


Record the measures of center and measures of variability for the above data.

Graph the number of coils and average distance you calculated. The number of coils (independent variable) is along the x-axis and the average distance (dependent variable) is along the y-axis.

Station 3:


Hold a magnet to the case following the directions at the station. Draw what you see in the space below.Electromagnet Parallel Electromagnet Perpendicular

Permanent Magnet Parallel Permanent Magnet Perpendicular

Summary Questions:


1. Did the pipe or the object affect the speed the object fell in the teacher demonstration? Why?

2. What battery gave out the most voltage? Support your answer with data you collected from Station 1.

3. Explain what happens to the size of the magnetic field as the number of coils changes. Use data from Station 2 to support your answer.

4. How can you prove there is a magnetic field? Support your answer with observations you recorded from Station 3.

Appendix L: Teacher Guide to Forces with Demonstrations


Content

1. Gravity (Dropped Objects Demonstration)

2. Magnetic Field (Magnet Demo)

3. Electric Field

4. Triboelectric Effect (Static Electricity Demo)

5. Electrostatic Induction (Can Demo)

6. Lenz’s Law (Pipes Demo)

7. Eddy Currents

8. Electromagnetism

9. Electromagnet (Electromagnet Demo)

1. Gravity (Dropped Objects Demonstration)

Newton publicized his Theory of Universal Gravitation in the 1680s. It basically set forth the idea that gravity was a predictable force that acts on all matter in the universe, and is a function of both mass and distance. The theory states that each particle of matter attracts every other particle (for instance, the particles of "Earth" and the particles of "you") with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.So the farther apart the particles are, and/or the less massive the particles, the less the gravitational force.

The standard formula for the law of gravitation goes: force,F=Gm1m2

r2

where G is the gravitational constant, m1 and m2 are the masses of the two objects for which you are calculating the force, and r is the distance between the centers of gravity of the two masses.G has the value of 6.67 x 10-8 dyne * cm2/gm2. 6.67 x 10-8 dyne is a miniscule force.G ~ 6.674 x 10-11 m3kg-1s-2 ~ 6.674 x 10-11N (m/kg)2 ~ 6.674 x 10-8 cm3g-1s-2

When you deal with massive bodies like the Earth, however, which has a mass of 6 x 10-24

kilograms, it adds up to a rather powerful gravitational force. That's why you're not floating around in space right now.



The force of gravity acting on an object is also that object's weight. When you step on a scale, the scale reads how much gravity is acting on your body.

• The formula to determine weight is weight,W=m×g

where m is an object's mass, and g is the acceleration due to gravity. Acceleration due to gravity on Earth, is 9.8 m/s² (32.2 ft/s²) -- it never changes, regardless of an object's mass.That's why if you were to drop a pebble, a book and a couch off a roof, they'd hit the ground at the same time.

Dropped Objects Demonstration!!!

2. Magnetic Field (Magnet Demo)

• A magnetic field is the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field.

• The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter (symbol: A·m-1 or A/m) in the SI. B is measured in teslas (symbol: T) and newtons per meter per ampere (symbol: N·m-

1·A-1 or N/(m·A)) in the SI. B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges.

• Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin.

• In everyday life, magnetic fields are most often encountered as a force created by permanent magnets, which pull on ferromagnetic materials such as iron, cobalt, or nickel and attract or repel other magnets. Magnetic fields are widely used throughout modern technology, particularly in electrical engineering and electromechanics The Earth produces its own magnetic field, which is important in navigation, and it guards Earth's atmosphere from solar wind. Rotating magnetic fields are used in both electric motors and generators.

Magnetic field of an ideal cylindrical magnet with its axis of symmetry inside the image plane. The magnetic field is represented by magnetic field lines, which show the direction of the field at different points

The direction of magnetic field lines represented by the alignment of iron filings sprinkled on paper placed


Permanent Magnet Demonstration!!!3. Electric Field

• The electric field is a component of the Electromagnetic field. It is a vector field, and it is generated by electric charges or time-varying magnetic fields as described by Maxwell's equations.

• The concept of an electric field was introduced by Michael Faraday.

• Electric fields are caused by electric charges or varying magnetic fields. The former effect is described by Gauss's law, the latter by Faraday's law of induction, which together are enough to define the behavior of the electric field as a function of charge repartition and magnetic field. However, since the magnetic field is described as a function of electric field, the equations of both fields are coupled and together form Maxwell's equations that describe both fields as a function of charges and currents.

4. Triboelectric Effect (Static Electricity Demo)

Electric field lines emanating from a point positive electric

Illustration of the electric field surrounding a positive (red) and a negative

Electric field induced by a positive electric charge (left) and a field induced by a negative electric charge (right).

Contact with the slide has left this child's hair positively charged so that the individual


• Definition – The generation of static electricity by friction between different materials.

• The triboelectric effect (also known as 'triboelectric charging') is a type of contact electrification in which certain materials become electrically charged after they come into contact with another different material and are then separated (such as through rubbing). The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties. The triboelectric effect is responsible for the shock you receive from a car door after you slide out. (Wikipedia)

• The first account of static electricity is believed to date back to 600 BC when a Greek philosopher Thales of Miletus rubbed amber with silk and produced a static charge. The Greek word for amber was elekron and it is from this that we derive our word electricity.

• Air molecules will ionize if the electric field gradient exceeds the breakdown strength of air (~3000 volts/millimeter depending on humidity and the point size).

• The magnitude of the static charge is determined by material composition, applied forces, separation rate, and relative humidity.

Triboelectric Series

Common materials are listed according how well they create static electricity when rubbed with another material, as well as what charge the material will possess.


The best combinations of materials to create static electricity would be to have one material from the positive charge list and one from the negative charge list. Examples include combining human skin with polyester clothes, combing your hair with a plastic comb, and rubbing fur on a Plexiglas rod.

Skin and polyester clothes: A common complaint people have in the winter is that they shoot sparks when touching objects. This is typically caused because they have dry skin, which can become highly positive (+) in charge, especially when the clothes they wear are made of polyester material, which can become negative (-) in charge.

People that build up static charges due to dry skin are advised to wear all-cotton clothes, which is neutral. Also, moist skin reduces the collection of charges.

Combing your hair: Human hair becomes positive (+) in charge when combed. A hard rubber or plastic comb will collect negative (-) charges on its surface. Since similar charges repel, the hair strands will push away from each other, especially if the hair is very dry. This is called "flyaway" hair. Since the comb is negatively charged, it will attract object with a positive charge—like hair. It will also even attract material with no charge—like small pieces of paper.

Fur and Plexiglas rod: Rubbing a Plexiglas rod with rabbit fur or wool will give the rod a negative charge. Although the rod can be used to pick up scraps of paper, the fur and wool quickly lose their charge.

Static Electricity Demonstration!!!


5. Electrostatic Induction (Can Demo)

• Electrostatic induction is a redistribution of electrical charge in an object, caused by the influence of nearby charges. In the presence of a charged body, an insulated conductor develops a positive charge on one end and a negative charge on the other end. Induction was discovered by British scientist John Canton in 1753 and Swedish professor Johan Carl Wilcke in 1762. Electrostatic generators, such as the Wimshurst machine, the Van de Graaff generator use this principle. Due to induction, the electrostatic potential (voltage) is constant at any point throughout a conductor. Induction is also responsible for the attraction of light nonconductive objects, such as balloons, paper or Styrofoam scraps, to static electric charges. Electrostatic induction should not be confused with electromagnetic induction.

• A normal uncharged piece of matter has equal numbers of positive and negative electric charges in each part of it, located close together, so no part of it has a net electric charge. The positive charges are the atoms' nuclei which are bound into the structure of matter and are not free to move. The negative charges are the atoms' electrons. In electrically conductive objects such as metals, some of the electrons are able to move freely about in the object.

• When a charged object is brought near an uncharged, electrically conducting object, such as a piece of metal, the force of the nearby charge due to Coulomb's law causes a separation of these internal charges. For example, if a positive charge is brought near the object the electrons in the metal will be attracted toward it and move to the side of the object facing it. When the electrons move out of an area, they leave an unbalanced positive charge due to the nuclei. This results in a region of negative charge on the object nearest to the external charge, and a region of positive charge on the part away from it. These are called induced charges. If the external charge is negative, the polarity of the charged regions will be reversed.

• Since this process is just a redistribution of the charges that were already in the object, it doesn't change the total charge on the object; it still has no net charge. This induction effect is reversible; if the nearby charge is removed, the attraction between the positive and negative internal charges causes them to intermingle again.

Charged Can Demonstration!!!


6. Lenz’s Law (Pipes Demo)

• Lenz's law is a common way of understanding how electromagnetic circuits obey Newton's third law and the conservation of energy. Lenz's law is named after Heinrich Lenz, and it says:

– If an induced current flows, its direction is always such that it will oppose the change which produced it.

• Lenz's law is shown with the negative sign in Faraday's law of induction:

ε=−∂Φ∂ t

• this indicates that the induced voltage (E) and the change in magnetic flux (?Φ) have opposite signs. Lenz's Law is a qualitative law that refers to the direction of induced current in relation to the effect which produces it without quantitatively relating their magnitudes.

• Example: Currents bound inside the atoms of strong magnets can create counter-rotating currents in a copper or aluminum pipe. This is shown by dropping the magnet through the pipe. The descent of the magnet inside the pipe is observably slower than when dropped outside the pipe.

Pipes Demonstration!!!A great example of Lenz's law is to take a copper tube (it's conductive but non-magnetic) and drop a piece of steel down through the tube. The piece of steel will fall through, as you might expect. It accelerates very close to the acceleration due to gravity. (Only air friction and some possible rubbing against the inside of the tube prevent it from reaching the acceleration due to gravity.)Now take the same copper tube and drop a magnet through it (hopefully a strong one, Neodymium or other rare earth magnets work the best) You will notice that the magnet falls very slowly. This is because the copper tube "sees" a changing magnetic field from the falling magnet. This changing magnetic field induces a current in the copper tube.The induced current in the copper tube creates its own magnetic field that opposes the magnetic field that created it.

7. Eddy Currents

When a conductor moves through an inhomogeneous field generated by a source, electromotive forces (EMFs) can be generated around loops within the conductor. These EMFs acting on the resistivity of the material generate a current around the loop, in accordance with Faraday's law of induction. These currents dissipate energy, and create a magnetic field that tends to oppose changes in the current- they have inductance.


Eddy currents are created when a conductor experiences changes in the magnetic field. If either the conductor is moving through a steady magnetic field, or the magnetic field is changing around a stationary conductor, eddy currents will occur in the conductor. Both effects are present when a conductor moves through a varying magnetic field, as is the case at the top and bottom edges of the magnetized region shown in the diagram. Eddy currents will be generated wherever a conducting object experiences a change in the intensity or direction of the magnetic field at any point within it, and not just at the boundaries.

Eddy currents (I, red) induced in a conductive metal plate (C) as it moves to right under a magnet (N). The magnetic field (B, green) is directed down through the plate. From Lenz's law the increasing field at the leading edge of the magnet (left) induces a counterclockwise current, which creates its own magnetic field (left blue arrow) directed up, which opposes the magnet's field, producing a retarding force. Similarly, at the trailing edge of the magnet (right), a clockwise current and downward counterfield is created (right blue arrow) also producing a retarding force.

http://upload.wikimedia.org/wikipedia/commons/c/c6/Eddy_currents_due_to_magnet.s


8. Electromagnetism

Electromagnetism is the study of the electromagnetic force which is a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually manifests as electromagnetic fields, such as electric fields, magnetic fields and light. The electromagnetic force is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction, and gravitation.

The word electromagnetism is a compound form of two Greek terms, ēlektron, "amber", and, magnetic, from "magnítis líthos“, which means "magnesian stone", a type of iron ore. The science of electromagnetic phenomena is defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as elements of one phenomenon.

The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. Ordinary matter takes its form as a result of intermolecular forces between individual molecules in matter. Electrons are bound by electromagnetic wave mechanics into orbitals around atomic nuclei to form atoms, which are the building blocks of molecules. This governs the processes involved in chemistry, which arise from interactions between the electrons of neighboring atoms, which are in turn determined by the interaction between electromagnetic force and the momentum of the electrons.

Lightning is an electrostatic discharge that travels between two charged regions.


9. Electromagnet (Electromagnet Demo)

An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. Electromagnets usually consist of a large number of closely spaced turns of wire that create the magnetic field. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of electrical energy to maintain a magnetic field.Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment. Electromagnets are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel.

Electromagnet Demonstration!!!

A simple electromagnet consisting of a coil of insulated wire wrapped around an iron core. The strength of magnetic field generated is proportional to the amount of current.

Magnetic field produced by a solenoid (coil of wire). This drawing shows a cross section through the center of the coil. The crosses are wires in which current is moving into the page; the dots are wires in which current is moving up out of the page.

Electromagnets in an electric bell


Backup Reference – Maxwell’s Equations

• Where the universal constants appearing in the equations are the permittivity of free space ε0 and the permeability of free space μ0.

• In the differential equations, a local description of the fields, the nabla symbol ? denotes the three-dimensional gradient operator, and from it the divergence operator is ?· the curl operator is ?×.

• The sources are taken to be the electric charge density (charge per unit volume) ρ and the electric current density (current per unit area) J.

• In the integral equations; a description of the fields within a region of space, Ω is any fixed volume with boundary surface ?Ω, and Σ is any fixed open surface with boundary curve ?Σ,

Here "fixed" means the volume or surface does not change in time. Although it is possible to formulate Maxwell's equations with time-dependent surfaces and volumes, this is not actually necessary: the equations are correct and complete with time-independent surfaces. The sources are correspondingly the total amounts of charge and current within these volumes and surfaces, found by integration.

The volume integral of the total charge density ρ over any fixed volume Ω is the total electric charge contained in Ω:

where dV is the differential volume element, and the net electrical current is the surface integral of the electric current density J, passing through any open fixed surface Ó:

where dS denotes the differential vector element of surface area S normal to surface Ó. (Vector area is also denoted by A rather than S, but this conflicts with the magnetic potential, a separate vector field).

The "total charge or current" refers to including free and bound charges, or free and bound currents.

is a line integral around the curve ∂Ó (the circle indicates the curve is closed).

is a surface integral over the surface Ó,is a volume integral over the volume

is a surface integral over the surface ∂Ù (the oval indicates the surface is closed and not open


Appendix M: Teacher Resource – Mousetrap DesignsHumane Trap DesignsThis reference sheet provides a variety of simple mouse trap designs, along with the required materials and tools. The students use gravitational and magnetic forces to trap mice for humane release.

Bucket & Spoon

Description: A spoon is balanced on the edge of a counter top over a deep bin or bucket with peanut butter on the suspended end. The mouse tips the balance of the spoon and falls into the bucket.

Materials: bucket, spoon, bait

Tools: none

Bucket & Cardboard Tube

Description: This trap employs the same concept as above, but it uses an empty toilet paper roll with two quarters taped on top and centered for balance. The mouse tips the balance of the roll and falls into the bucket.

Materials: bucket, empty toilet paper roll, 2 quarters, tape, bait

Tools: none


Bucket & Soda Bottle

Description: A small plastic soda bottle has a rod pierced through the center of the bottom and cap. The rod ends are mounted to the top of a bucket to allow it to easily spin on its axis. A ramp is set up to allow a mouse to reach the rim of the bucket. Peanut butter is spread on the middle of the plastic bottle. The mouse will attempt to reach the bait and fall in the bucket.

Materials: bucket, water/soda bottle, thin rod (metal, wood, or plastic), bait

Tools: drill

Bucket & Paper Plate

Description: This trap employs a similar concept to the previous idea, except a paper plate is used. One lip of the plate is on the bucket edge and the opposite end has the bait. A rod is placed very slightly off-center through the paper plate, allowing it to flip with the weight of the mouse, trapping it in the bucket

Materials: bucket, paper plate, thin rod (metal, wood, or plastic), bait

Tools: none

Glass & Coin

Description: A glass is propped-up by a quarter with peanut butter spread on the inside. The movement of the mouse triggers the fall of the glass.

Materials: glass, quarter, bait

Tools: none


Inverted 2-Liter with One-Way Opening

Description: A plastic 2-liter container is cut around its circular exterior about 2/3 up from the base. The top is inverted and rested inside the base segment. Tape is used to secure the pieces together and to hold the bottle to the surface.

Materials: 2-liter plastic bottle, tape, bait

Tools: box cutter

Magnet as a Weak Trap Door

Description: A weak magnet is used to suspend a small platform or doors (trap door) with hinges over a box that is 6 inches or greater in depth. The weight of the mouse will exceed the strength of the magnetic force holding the platform in place.

Materials: box, weak magnets, bait, thin rod or plastic stirrer (hinges)

Tools: scissors


Locking Magnetic Plank

Description: This trap uses a rectangular cavity with a small platform that is almost center balanced. When the mouse walks up the platform, it falls and the opposite side goes up to the top of the entrance. Small magnets on the elevated end stick to the ceiling lock together and trap the mouse.

Materials: box, weak magnets, bait, thin rod or plastic stirrer (hinges)

Tools: scissors

Generic Catch Trap with Magnets

Description: This trap uses a rectangular box with one open end and one closed end. The closed end has a sensitive pressure plate that depresses with the mouse’s weight, separating weak magnets, and releasing the door over the opening. Small magnets are used to keep the door shut.

Materials: box, weak magnets, string, bait, thin rod or plastic stirrer (hinges)

Tools: scissors

Images only include graphics with an unlimited commercial license; see https://openclipart.org/share.


Appendix N: Engineering Design ChallengeName______________________________

Your team has been assigned a type of animal and number of forces that must be used in the trap design. Your group will design, build and test a trap that uses the number of forces assigned to humanely trap the animal (minimal contact with animal). Depending on the results of the trap testing of the original design, you will redesign and re-test based to meet the original performance criteria or maintain performance while reducing the cost of the design. You group needs to create detailed sketches of original and redesigned trap (including dimensions) and a bill of materials (cost of raw materials to make the trap) for the original and redesign and calculate cost reduction. Your team will present and defend original and redesigned traps; bill of materials and reduction of cost.


Appendix O: Engineering Design Challenge RubricName _____________________________

Category 4 3 2 1 Design Criteria and Performance EvaluationForces Used Students correctly

label, explain, and implement the force(s) used

Students correctly explain and label the forces used.

Students label the forces but do not explain

Students do not label OR explain the forces used.

Trap Humanly Catches Animal

Design catches animal with minimum physical contact with animal

Design catches animal with minor physical contact with animal

Design catches animal with physical contact to animal

Design does not catch animal

DeliverablesPresentation Team is able to defend

their design including what materials were used, how their design works, what they learned, why this design is humane.

Team is able to defend their design including 3 of the following: what materials were used, how their design works, what they learned, why this design is humane.

Team is able to defend their design including 2 of the following:What materials were used, how their design works, what they learned, why this design is humane.

Team is able to defend their design including 1 or none of the following: what materials were used, how their design works, what they learned, why this design is humane.

Formal Sketch of Design

Team provides a detailed formal sketch of the design. The design is legible, is labeled and includes measurements in metric

Team provides a detailed sketch of the design with 2 of the following: The design is legible, is labeled and includes measurements in metric

Team provides a detailed sketch of the design with 1 of the following: The design is legible, is labeled and includes measurements in metric

Team provides a detailed sketch that does not include: The design is legible, is labeled and includes measurements in metric OR the sketch is not included

Design Scalability for different animals

Students include how their design can be scaled both up and down

Students include how their design can be scaled up or down

Students do not accurately scale their project

Students do not include how to scale their project

Cost – Bill of Materials

Team provides detailed bill of materials worksheet. It must be legible, includes all raw materials in design, costs calculated correctly.

Team provides detailed bill of materials worksheet with 2 of the following: it must be legible, includes all raw materials in design, costs calculated correctly.

Team provides detailed bill of materials worksheet with 1 of the following: it must be legible, includes all raw materials in design, costs calculated correctly.

Team provides detailed bill of materials worksheet does not include: it must be legible, includes all raw materials in design, costs calculated correctly OR the worksheet is not included

REDESIGN performance and cost reduction

Original design meets both Design Criteria.Redesign meets BOTH Design Criteria AND reduced cost of trap

Original design meets both Design Criteria.Redesign does not meet both of the Design Criteria AND reduced cost of trap.

Original design meets only 1 of the Design Criteria.Redesign meets BOTH Design Criteria.

Original design meets only 1 of the Design Criteria.Redesign meets only 1 of the Design Criteria.


Appendix P: Bill of MaterialsName _____________________________

Name of Raw Material

Cost per unit of Raw Material

Number of Units of Raw Material Needed for Original Design

Subtotal of Raw Material Cost for Original Design

Number of Units of Raw Material Needed for Redesign

Subtotal of Raw Material Cost for Redesign

Cost Reduction from Original Design to Redesign (in %)

TOTAL COST of all Raw Materials


Appendix Q: Presentation GuidelinesName _____________________________

For Days 9-10: Presentations

Your team will create a presentation to share with the entire class.

The audience for the presentation is Billy the Exterminator’s representative who is going to decide if Billy wants to select and buy your trap design.

Each team member will present a different aspect of the project:

- Mechanical Engineer o Explain how the redesigned trap workso Why they chose specific design elementso Explain how the forces were used in the design

- Project Manager o Describe the original designo Explain what they learned from their original design and how they used that

information in the redesigno Present final testing results for the redesign

- Materials Engineer o Describe why they chose specific materials for the original and redesign and cost

reductiono Explain the Bill of Materials

- Biologist o Describe the critical attributes of the animalo Explain why the original and/or redesign trap is humane

- Each team member o Explain if they could do one more redesign, what would they change?


Appendix R: Brief Technical Discussion of Gravitational and Electromagnetic ForcesThe following brief description of gravitational, electrical, and magnetic forces is more in

depth than a middle school student needs to know, but a solid foundation in these basic physical concepts may allow the instructor to correct common misconceptions held by students.

Gravitational and electromagnetic are two of the four known fundamental forces that govern how matter interacts throughout our universe. All forces act at a distance through all kinds of media (i.e., air, water, or solid materials) even when there is no material present such as the vacuum of outer space. The SI unit of all forces is the Newton (N), which is equivalent to 1kg ∙m /s2 in base units.

Gravitational force describes the force present between two objects and is proportional to the mass of the two objects and inversely proportional to the square of the distance, as

described by,f grav=Gm1m2

d2 , where m1and m2 are the mass of the two objects and d is the

distance between the them.Gis thegravitational constant, sometimes called the Newtonian constant of gravitation (G=6.673∙10−11N (m /kg )2). Big G is often confused for little g which is the Earth’s acceleration of object due to gravity. Big G is a constant that explains behavior throughout the universe, and little g describes acceleration due to the Newtonian force of Earth’s gravity. On average,g≅ 9.81m /s2 on the Earth’s surface.

A free body diagram is used to describe the magnitude and direction of forces on a body. If all of the force vectors (direction and magnitude) sum to zero, the body will be in equilibrium. A common misconception is that forces causes motion – forces cause acceleration which is a change in the motion. Consider the forces of a hockey puck on a frictionless surface like ice. There is a Newtonian (gravitational) force pointed downward. This is the force on the hockey puck due to the mass of the Earth. There also exists an equal and opposite force, pointed upward, describing the force on the Earth due to the mass of the hockey puck. Even though the mass of the Earth is much bigger than the mass of the hockey puck the forces are equal, since the gravitational force depends on the mass of both objects.

Another common misconception is that motion of objects implies a force has been applied. Since these forces balance, the hockey puck does not experience acceleration. It may in fact be moving with a constant velocity. Consider a situation where the hockey puck is moving across a frictionless surface like ice. If the hockey puck changes its velocity (from stationary to moving or from moving to stationary) then there must have been a force applied, but the hockey puck could be moving with a constant velocity even if all the forces are balanced. Recall Newton’s third law of motion: objects in motion stay in motion.

Objects in free-fall are accelerating due to the gravitational force. That is, they are falling faster and faster at a rate of 9.81m /s2, independent of their mass. A third common misconception is that heavier objects (those with more mass) fall faster than lighter objects. Our common experience often includes the non-negligible effects of friction due to air resistance, leading to this incorrect belief. By definition, weight (SI unit is N) is the gravitational force on an object in the presence of a much larger object like the earth. Mass (SI unit is kg) is often confused with weight. While mass is a fundamental property of an object, the weight of the object depends on the gravitational force field that it resides in.

The electromagnetic force describes the influence of electrical charge on objects. When charged objects are accelerating, the electric and magnetic forces are coupled and more complicated to explain. We will consider here only static electric and magnetic forces, which can be treated separately, even though both forces may co-exists.


The static electric force between two charged particles is described by Coulomb’s law:

f elec=Kq1q2

d2 , where q1and q2 are the charges of the two objects and d is the distance between

the them. K is a constant that depends on the material properties in the medium. It is interesting to note the similarity of the equation for gravitational force and electrical force. Both forces are weaker when the objects are further apart. However, since charge can be positive or negative, the electrical force can be an attractive force (when charges are different signs) or a repulsive force (when both charges are the same sign). In contrast, the gravitational force is always an attractive force because mass is strictly a positive quantity. Static charges (those that don’t move) experience equal and opposite forces. For example, the magnitude of the electric force on an electron (q1=−1.602⋅ 10−19C) due to the proton (q2=+1.602⋅10−19C) is equal to the magnitude of the electric force on the proton due to the electron and they are in opposite directions indicating that if they are free to move they would be accelerated towards each other.

It’s also interesting to know that the electric force is much stronger than the gravitational force. For example, the gravitational force of two protons is orders of magnitude weaker than the electrical force of the two protons at the same distance. This is counter-intuitive since, in our common experience, most matter is made up of many positive and negative charges whose forces cancel each other out and we only experience static electric force in special situations where there exists a net build-up of (either positive or negative) charge. One common example is static electricity. In this situation materials are rubbed together (for example human dry hair and a plastic balloon), transferring kinetic energy to electrical energy which separates positive charge from negative charge. The hair tends to give up electrons and becomes (net) positively charged and the plastic becomes negatively charged, so the two objects attract each other. The influence of the electrical force can only be observed when these two objects are close enough, because the force gets much weaker as distance is increased. If the positively charged balloon is far enough away from the hair, or the hair becomes neutrally charge we may not observe the effect of the electric force even though its electrical potential still exists. A common way to describe the influence that a charged object can exert on another charged object is to draw its electric field intensity map (or electric field). The electric field of an object describes the electrical force per unit charge at all points in space. The electric field is a vector field (as opposed to a scalar field) its SI unit is N/C but it’s commonly converted to V/m. The electric field describes both the magnitude of the electric force and the direction. Since the electric field is equal to the electrical force per unit charge the electric field does not depend on the magnitude of the charge. By convention electric fields emanate from positive charge and terminate on negative charge. The direction and relative magnitude of the electric field map depend on the spatial distribution of the charges.

The source of static magnetic force is currents. Electrical charges moving at a constant velocity (no acceleration) can be described by a constant current. The Biot-Savart Law describes the magnitude and direction of the magnetic force. Similar to gravitational and electrical force, the magnetic force is also inversely proportional to the square of the distance between two currents. However, the direction of the magnetic force is always transverse to the direction of the current so it’s a little more complicated to describe. The most common way to describe the magnetic force is by drawing the magnetic field map. The magnetic field is usually described in units of A/m. The magnetic field intensity can be confused with the magnetic flux density, measured in the SI unit, Tesla, or the common unit, Gauss. Both field patterns look the same, but the magnetic flux density is independent of the material properties of the medium. An important difference between magnetic and electric fields is that the electric fields are open lines, and magnetic fields are closed lines, meaning they always form a closed loop. In a permanent magnetic, the source of the magnetic force is microscopic current loops formed due to the molecular structure of the material, which we don’t easily observe.


A non-moving charge has a static electric field associated with it, but not a magnetic field. Charges that are moving with constant velocity have a changing electric field (non-static) as well as a static magnetic field associated with them. Charges that are accelerating (implies currents change with time and/or direction) will generate dynamic electric and magnetic fields. For harmonically oscillating currents, electromagnetic waves are generated.

An electrical circuit is a system designed to use the electromagnetic force to deliver or convert energy. In a circuit, electric and magnetic fields exist, but they are more complicated to describe since they are not static fields. Therefore we usually analyze an electrical circuit by studying the flow of electric charges, or current. Current is the rate of net positive charge passing through a surface (like the cross-sectional of a wire) and is measured in units of Amperes, which is equal to 1C/s. Electrical circuits usually incorporate an electrical source (like a battery, or a generator), an electrical sink (like a resistor, light bulb, or electric motor) connected together in a closed circuit by conductive wire. A battery stores energy and delivers (though an electro-chemical conversion) energy to a circuit. A generator generates electromagnetic energy by using mechanical energy to cause a changing magnetic field (e.g., physically moving a permanent magnet) in a coil of wire, inducing a current flow in that wire. This process is described by Faraday’s law of induction. Faraday’s law of induction also explains how a changing electrical current can induce a magnetic field. This is called an electromagnet. An electromagnetic motor uses an electromagnet to convert electrical energy to kinetic energy and turn a rotor. A key difference between an electromagnet and a permanent magnet is that the electromagnet can be turned on and off, and the polarity can be changed by controlling the current in the wire.

Resources

1. The National Institute of Standards and Technology disseminates values of fundamental physical constants, related SI units, and related information on material properties (http://physics.nist.gov/cuu/index.html)

2. The American Psychological Association describes some common alternative science conceptions (misconceptions) held by junior and high school students (http://apa.org/education/k12/alternative-conceptions.aspx)

http://apa.org/education/k12/alternative-conceptions.aspx

http://physics.nist.gov/cuu/index.html


Appendix S: Testing – Data Collection SheetName ___________________________Testing – Data Collection Sheet

Record the collected data from your trials below. Be sure to complete the follow up questions.

Trial Time Trapped Outcome(Describe how it was caught – fully, partially, not at all)

#1

#2

#3

#4

#5

Follow-up questions:1. Calculate the mean time it took to trap your animal.

2. If there are any outliers, re-calculate your mean excluding them.

3. List possible modifications your team can make to your trap that would improve either the time it took for your trap to work, effectiveness of your trap, or both.


Appendix T: Design Scalability WorksheetList all labeled dimensions on the sketch of the redesigned trap

Scale trap design for a male African elephant. Show your work.Weight: 15,000 lb.Height: 9 feetBody length: 18 feetMoving speed: 1 miles per hour

Scale trap design for a snail. Show your work.Weight: 2 ouncesHeight: 1 inchBody length: 1 inchMoving speed: 50 yards per hour

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