1. How are energy and work related?

Warm up…

Chapter 5 Section 1

Energy is the ability to do work Work is the transfer of energy

◦ Force moves an object Measured in Joules (J)

What are some things that make a job feel like more work?

Energy…

How are energy and work being done during this tennis match?

How are energy and work being done

during a golf tournament?

Energy of MOTION Depends on speed and mass KE = mv2

2

LOOK at the formula…

Which has a greater effect on KE, mass or speed?

Why/how do you know?

Kinetic Energy

INDEX CARDENERGY UNIT FORMULAS…

KE = mv2 2

Which has more KE-the red car or green car? Explain.

Which has more KE-the red car or truck? Explain.

A snail with a mass of 5 g traveling at 0.014 m/s has a KE of 0.00000048 J!

An 18-wheel truck traveling at 44 mi/h has a KE of 2,200 J!

Weird Science...

1. Provide a caption for your work/energy picture

2. Label any area where work is being done (you should have at least 2 places where you have shown some work)

3. Put your name and class period on the back of your illustration

On the back of your paper, please explain the following

in a short paragraph:

-Energy-Work

-How your picture demonstrates these 2 ideas

1. What is your hypothesis for the rubber band racers?

2. What is the independent variable?

3. The dependent?

Warm up…

Rubber Band Racers…

1. Build your car quickly; divide the jobs and work as a team

2. Begin with 1 energy unit (1 winding) and run 3 trials for each number of windings; collect data

3. Average the data for each energy unit4. Graph the average data for distance vs the

energy units5. YOU MUST MEASURE DISTANCE IN METRIC

1. Was your hypothesis for your racer correct? Why?

2. What is a good title for the graph you will create with this data?

Warm up…

1. What are the 2 factors that determine the KE of an object?

Warm up…

KE FACTORS DEMO…

1. Copy the chart below into your notes.

2. Using the setup described on the paper at your table, launch the lid with the discs. Record your data.

# Washers Distance Traveled

1

3

5

3. Quickly graph your data.4. Answer the 3 questions below:

5. What was the trend you observed as you increased the # of washers you launched?

2. Using your graph, what would the distance have been for 2 washers?

3. What is the independent variable in this quick demo? Why/Explain.

KE PROBLEMS…

1. What is the kinetic energy of a car that has a mass of 1,200 kg and is moving at a speed of 20 m/s?

2. What is the kinetic energy of a car that has a mass of 2,400 kg and is moving at a speed of 20 m/s?

3. How does the kinetic energy of the 2 cars above compare? What do you notice?

1. What are the 2 factors that determine the KE of an object?

2. What is the formula for KE?3. Which factor has a greater

impact on KE?

Cool down…

1. What are the 2 factors that determine the KE of an object?

2. What is the formula for KE?3. Which factor has a greater

impact on KE?

Warm up…

Energy of POSITION or SHAPE Depends on weight and height The amount of work done to get object in

that position. GPE = weight x height

What’s the difference between weight & mass?

Potential Energy

INDEX CARDENERGY UNIT FORMULAS…

KE = mv2 2

GPE = weight x height

Does Diver A or B have more GPE?

Which Diver did more work?

Diver A 450 N

Diver B 500 N

Does Diver C or D have more GPE?

Which Diver did more work?

Diver D 550 N

Diver C 550 N

Which Diver did the most work?

Diver D 550 N

Diver C 550 NDiver A

450 NDiver B 500 N

GPE PROBLEMS…

1. What is the gravitational potential energy of a book with a weight of 13 N at

a height of 1.5 m off the ground?

2. What is the gravitational potential energy of a cat that weighs 40 N standing on a table that is 0.8 m above the ground?

The sum of the kinetic and potential energy. ME = KE + PE

Mechanical Energy

INDEX CARDENERGY UNIT FORMULAS…

KE = mv2 2

GPE = weight x height

ME = KE + PE

Weight = 200 N

Mass = 20 kg

Hei

ght =

5 m

What is GPE of the car?

What is KE of the car?Speed = 0 m/s

Weight = 200 N

Mass = 20 kg

Hei

ght =

5 m

GPE = Wt * Ht = 200 * 5 GPE = 1,000 J

KE = m * v2 / 2 = 20 *02 / 2

KE = 0 JSpeed = 0 m/s

1. What is the difference between GPE and KE?

2. Why do we use mass for KE and weight for GPE?

Warm up…

Weight = 200 N

Mass = 20 kg

Hei

ght =

5 m

What is the ME for this system?

Speed = 0 m/s

Weight = 200 N

Mass = 20 kg

Hei

ght =

5 m

ME = KE + PE

ME = 0J + 1,000J

ME = 1,000JSpeed = 0 m/s

Weight = 200 N

Mass = 20 kg

Hei

ght =

5 m

What is GPE of the car now?

What is KE of the car now?

Speed = 10 m/s

Weight = 200 N

Mass = 20 kg

Hei

ght =

5 m

Speed = 10 m/s

GPE = Wt * Ht = 200 * 0 GPE = 0 J

KE = m * v2 / 2 = 20 *102 / 2

KE = 1,000 J

1. What kind of energy is found in a stretched rubber band? Explain.

2. What kind of energy in found in a rubber band that has been released? Explain.

Warm up…

1. On a ramp, where would you find the most potential energy?

2. Where would you find the most kinetic energy?

Warm up…

Weight = 200 N

Mass = 20 kg

Hei

ght =

5 m

Speed = 10 m/s

What is the ME for this system?

Weight = 200 N

Mass = 20 kg

Hei

ght =

5 m

Speed = 10 m/s

ME = KE + PE

ME = 1,000J + 0J

ME = 1,000J

GPE = 1,000J

KE = 0J

GPE = 0J

KE = 1,000J

What’s happening to the GPE as he rolls down the hill?

Height decreases so GPE decreases

What’s happening to the KE as he rolls down the hill?

Speed increases so KE increases

If the ME for this system is 1,000J, what would expect the GPE and KE to be at the half way point?

ME = 500J + 500J

More KE, less GPE

Almost all KE now

Wait a minute, Mrs. Lock! When we tested this in the lab, the KE

at the bottom was LESS than the GPE at the top. WHY???

Where did the energy go?

GPE = 0J

KE = 1,000J850J

Some energy was changed into heat and sound as the car

wheels rubbed against the ramp.

GPE = 0J

KE = 1,000J850J

ME = KE + PE + friction!

1. How does a pendulum show KE and GPE?

Warm up…

1. What is the GPE at Point A?2. What is the ME for the

picture?3. What is the GPE at Point B?4. What is the approximate KE

at Point B?

Warm up…

100 N

20 M

10 M

1. How does a pendulum show energy conversions?

2. What is the law of Conservation of Energy?

Warm up…

Info: We want to see what affects the time a pendulum takes to swing. Time period is the time for a full swing (forward and backward). Question: How does length of the pendulum affect its time period?

A PENDULUM EXPERIMENT

Question: How does length of the pendulum affect its time period?

Write your hypothesis using the question above. Remember it MUST be an “If…then…” statement.

Use an independent and a dependent variable

Data: Copy the chart below:

Length of

String (m)

Time for 20 Swings

(s)

Time for 1 Swing (s)

1

2

3

4

5

6

7

8

9

10

Steps: 1. Measure the length of string 2. Measure the time for 20 full swings 3. Divide by 20 to find the time for 1 swing. 4. Repeat this for 9 additional string lengths5. Graph the data (independent variable on the x-axis, dependent on the y-axis)

1. What is happening to energy at the top of a jump on a trampoline?

2. At the bottom?

Warm up…

Steps: 1. Graph the data (independent

variable on the x-axis, dependent on the y-axis)

2. Respond to the following on your graph paper in a good paragraph:

Was your hypothesis correct or incorrect? Why? Explain how energy is transferred in a pendulum. How does the Law of Conservation of Energy Apply to a pendulum?

1. Describe the energy conversions that happen as a skier goes down the slope.

2. Does ME change along the way? Explain.

Warm up…

Wt=50N

1.What is the KE at point A?2.What is the PE at point A?3.What is the ME at point A?4.What is the PE at point B?5.Use ME(and PE) to find the KE at point C.

A.

B.C.

Show work on back Put answers on front

POP QUIZ