WARM UP – 11/13/12

How would you define the term force? What does a force do?

FORCES FOLDABLE: TITLE EACH FLAP AND DRAW A PICTURE, THEN INCLUDE ALL INFORMATION LISTED BELOW

What is a Force? (title) *Define: -Force -Newton -Net Force

Forces in the SAME direction vs. Forces in OPPOSITE direction (title)

*Define Each *How is net force determined? *Draw a diagram with arrows for each.

Balanced Forces (title)

*Define *Draw a Picture using arrows to show force size and direction

Unbalanced Forces (title)

*Define *Draw a Picture using arrows to show force size and direction

Forces all around us

The Nature of Force

• A force gives energy to an object, sometimes causing it to start moving, stop moving, or change direction.

• A force can be a push or pull.

• Newton: the unit used to express force (I pushed the chair with 50 N of force)

• Net Force: the combination of all forces acting on an object

Types of Forces

Contact forces are types of forces in which the two interacting objects are physically contacting each other.

Applied Force Frictional Force Tensional Force Normal Force Air Resistance Force

(which is a type of frictional force)

Spring Force

Action-at-a-distance forces are types of forces in which the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite a physical separation.

Gravitational Force Electrical Force Magnetic Force Centripetal Force

Forces Acting in the Same Direction

When multiple forces act upon an object in the same direction, you ADD the forces to find the net force acting on the object.

Forces Acting in Opposite Directions

When multiple forces act upon an object in the opposite directions, you SUBTRACT the forces to find the net force acting on the object.

Balanced Forces

Balanced forces cause NO CHANGE in motion

Forces that are in opposite directions and equal in size are called balanced forces.

When forces are balanced, there is no change in motion; there would be no overall force (net force) acting on the object.

Balanced Forces

Unbalanced Forces

Unbalanced forces cause a CHANGE in motion

Same direction When two forces are

acting in the same direction, they are added together.

The size of the arrow is relative to the strength of the force.

•This force is unbalanced because there is a change in motion

Unbalanced ForcesSame Direction

They each provide an “applied force” in the same direction. Meanwhile, gravitational force and frictional forces are working against them.

Since Frank and John’s combined forces are greater, then the piano moves!

The net force is “unbalanced”

Frank and John are pushing the piano on its wheels to move it.

Unbalanced Forces-Opposite directions

When two forces act in opposite directions, they combine by subtraction,

If one force is greater

than the other force, the object will move in the direction of the greater force (tug-of-war).

This force is unbalanced

because there is a change in motion

Unbalanced Forces In this game of tug of

war, the red dog is losing ground.

The applied force of the red dog is not as great as the applied force of the gray dog.

Net force is unbalanced, and in the direction of the gray dog.

RECOGNIZING FORCES

Choose from these forces

Applied Force Frictional Force Tensional Force Normal Force Air Resistance Force Spring Force Gravitational Force

A skydiver (who hasn't opened his parachute yet) falls at terminal velocity. Consider the forces acting on the skydiver.

A block rests on top of a table. Consider only the forces acting upon the block.

A block slides across the top of a table. Consider only the forces acting upon the block.

RECOGNIZING FORCES

Choose from these forces

Applied Force Frictional Force Tensional Force Normal Force Air Resistance Force Spring Force Gravitational Force

A block hangs at rest from the ceiling by a piece of rope. Consider the forces acting on the block.

A ball is shot into the air with a spring-loaded cannon. Consider the forces acting on the ball while it is in the air.

The wheels of a car are locked as it skids to a stop while moving across a level highway.

A car is attached by a cable to a moving truck and is being pulled along a level highway. Consider only the forces acting on the car.

Force Diagram

Force Diagrams

Applied Force

Force of Friction

Force of Gravity

Normal Force

Label the forces involved in Tom Brady’s winning Touchdown throw!

FRICTION

Friction is all around us. Caused by the minor bumps and jagged edges in all surfaces there is no way for humans to escape it! One source even called it “the ‘evil’ of all motion” (Jackson). There are 4 types of friction: static, sliding, rolling and fluid. Each of these have their own unique application and advantages. There are pro’s and cons to friction as well as ways to decrease friction. Understanding these things will help us use friction to our advantage as well as lessen it when it becomes a frustration in daily life.

WARM UP

In your own words, write a definition of the word friction. What is one way that friction can be increased?

FRICTION: A FORCE OPPOSING MOTION Friction is a force that acts in a direction

opposite to the motion of the moving object causing the moving object to slow down and finally stop.

Friction arises from the fact that objects and surfaces are not perfectly smooth.

The amount of friction between two surfaces depends on how hard the surfaces are forced together and on the materials of which the surfaces are made.

Sliding friction

When solid objects slide over each other, they produce sliding friction. In order to move the object you must exert a force larger than the force of friction.

The amount of sliding friction depends on:weight of the moving object.type of surface that the object is

sliding across.

Rolling friction

When an object rolls over a surface rolling friction is produced Produced by objects such as wheels

and ball bearings it tends to be less than that of

sliding friction.

Fluid friction As an object moves

through a fluid it produces fluid friction fluid friction is less

than sliding friction.

Air resistance is an example of fluid friction caused by the particles that make up air.

All liquids and gases are fluidsFriction also exists

when an object moves across or through a fluid.

Substance called lubricants (oil, wax, and grease), change sliding friction to fluid friction, thus reducing friction.

STATIC FRICTION When a force is

applied to an object but does not cause it to move.

The force of static friction balances the applied force.

Static friction disappears as soon as an object begins to move.

Friction: Is it helpful or harmful?

An example: In your car friction can be both helpful and

harmful, here is how: When you press on the breaks you cause friction

between them which HELPS slow down your car In this same car there is friction between the moving

parts in the engine. This friction causes the parts to wear out over time and therefore they must be replaced.

Friction between your foot and shoe can make holes in your socks!

Friction between your shoe and the floor helps you to stand upright.

WARM UP Give an example of

how friction can be harmful when running a car. Then give and example of how it could be helpful. Try to identify the type of friction involved in your example.

Friction Assignment:

You will create a poster advertising a type of friction. What your poster must include:

An illustration with the direction of forces and motion labeled. Make sure the size of your arrows match the size of the force.

Include in you poster the definition of friction and the definition of your chosen type of friction.

Include a statement explaining how friction is playing a roll in your illustration.

Be neat, creative and add some color to your poster!

Friction is not always a problem . . . as a matter of fact, in many cases it can be helpful.

•How might we lessen the amount of slide friction?

WARM UP

Significantly decreased gravity gives astronauts the sensation of being weightless and forces astronauts to make many adjustments in their activities. Write a paragraph explaining what you would like and dislike about living with reduced gravity.

WHY DOES AN APPLE FALL TOWARDS THE GROUND WHEN DROPPED?

Isaac Newton asked this question in 1665. The answer to this question gave birth to a

law…

THE LAW OF UNIVERSAL THE LAW OF UNIVERSAL GRAVITATIONGRAVITATION

All objects in the universe attract each other through gravitational force.

The size of this force depends on the masses of the objects and the distance between them.

So… Gravitational force increases as mass increases. Gravitational force decreases as distance increases.

How Mass Affects Gravitational Force:

How Distance Affects Gravitational Force:

On Earth, all objects experience a "downward" force of gravity.

The force of gravity on an object is always equal to the weight of the object.

Gravity is of great importance in the interaction of all objects in the universe; it binds us to the Earth, holds the Earth and all

planets in the solar system,

Gravity is what holds the universe together

Weight is a measure of the

force of gravity on an object

Metric or SI unit is the Newton (N)

•Your weight varies according to the force of gravity pulling on you

•The force of gravity varies according to the distance the object is from the center of the Earth.

- You weigh less on top of a mountain than you do at sea level.

Weight

CALCULATE YOUR WEIGHT

Weight (N) = Mass (kg) x 9.8 Your mass (kg) can be found in two ways….

Mass = your pounds ÷ 2.2 There are 2.2 lbs in 1 kg

Mass = your pounds x 0.4545 There is about 0.4545 kg in 1 pound

BALL DROP INVESTIGATION You have been given two balls, predict which

ball will hit the ground first if dropped from the same height.

Now, with your neighbor, try it! Were the results what you expected? Why or

why not? Now, predict what would happen is you

dropped a piece of paper and the golf ball. Now try it! – what happened? Were the

results what you expected? Why or why not? How could you get the paper to drop at the

same rate as the golf ball?

GRAVITY IN MOTIONGRAVITY IN MOTION

All objects fall to the ground at the same RATE because the acceleration due to gravity is the same for all objects. This is because heavier objects experience more

gravitational pull but are also harder to accelerate than a lighter object.

ACCELERATION DUE TO GRAVITY

ALL objects accelerate toward earth at a rate of 9.8 m/s/s.

How do we calculate an objects change in velocity during free fall? Change in velocity= g x t

g=acceleration due to gravity t=time

WARM UP 11/27

A girl goes to the doctor and finds that she weighs 95 pounds. What is her weight in Newtons? M = lb / 2.2 M = 95/2.2 M = 43.18 kg

W = kg*9.8 W = 43.18*9.8 W = 423.16 N

VELOCITY DUE TO GRAVITY PROBLEM

A boy standing on a high cliff dives into the ocean below and strikes the water after 3 seconds. What is the boy’s velocity when he hits the water?

V = g x t V = 9.8 m/s/s x 3 s V = 29.4 m/s downward

ONE MORE A foul ball is hit straight up in the air and falls

from the top of its motion for 1.4 seconds before being caught by the catcher. What is the velocity of the ball as it hits the catcher’s glove? V=g x t V=9.8 m/s/s x 1.4 s V= 13.72 m/s downward

A FEW MORE THINGS ON ACCELERATION DUE TO

GRAVITY

All objects fall to the ground at the same rate; HOWEVER, differences in the size, shape and speed of an object can increase or decrease air resistance.

As speed increases so does air resistance At a certain point the two will equal out and the object

will fall at its terminal velocity (a constant rate).

QUICK QUIZ

1. What is the difference between mass and weight?

2. What must you know in order to calculate the gravitational force between two objects?

3. Name three common items that could be used to increase friction.

Free Fall Terminal Velocity

gravity

Air Resistance

Gravity

Unbalanced Balanced

ORBITING OBJECTS INVESTIGATION

Swing the stopper on a string around in a circle observing all of the forces acting on the stopper. (Make sure to put space between you and your neighbor.)

Draw a picture of the stopper being swung in a circle.

Label all forces with direction acting on the stopper from the moment it begins to swing.

ORBITING OBJECTS QUESTIONS TO CONSIDER Answer the following below your diagram:

What force put the stopper into motion?What force is keeping the stopper in

motion?Why is the stopper moving in a circle?If you let go of the string, where would

the stopper go?What force is working against the

motion of the stopper?How is this similar and different from

the orbit of the moon around the earth?

Orbital Motion:

Gravity

Forward motion (inertia) of the space shuttle

Actual path of the

shuttle

WARM UP: 11/29

You’ve all heard the myth about the penny dropped from the empire state building. It says that if you were hit by this penny, you would be seriously injured. Based on what we learned about terminal velocity, do you think this myth is true? Why or why not?

Projectile Motion:

Horizontal motion (inertia)

Gravity Actual path of

baseball

PROJECTILE MOTION INVESTIGATION

You have been given 2 types of balls, try tossing each into the bowl.

Draw a diagram of the path of each ball as it leaves your hand and enters the bowl.

Label the forces involved with names and arrows, paying careful attention to the size of your arrows.

Which object was more difficult to throw into the bowl? Why?

WARM UP

If Wile E. Coyote and a boulder fall off a cliff at the same time, which do you think will hit the

ground first?

WARM UP

You throw a ball up into the air. It reaches a maximum height and then begins to fall back towards the ground. How fast is it traveling after it has been falling for 2.5 seconds? V = gt V = 9.8 * 2.5 V = 24.5 m/s downward

TOTD – 11/30/12

Suppose your friend asks you to tell them about projectile motion. You start to explain, but she interrupts. “Wait,” she says, “You’re using a lot of words I don’t understand. Can you explain in English?” Knowing that a picture is worth a thousand words, draw a picture of a projectile path and label all the key terms, including any necessary explanations.