# Work and Energy Chapter 4

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Work and Energy Chapter 4
Motion and Forces Work and Energy Chapter 4

Bell Work 2/22/11 Write each statement, then decide if the statement is true or false, if false correct it. An object has acceleration if its velocity is changing. Force is measured in joules. Gravity is a force.

How do you work? Do you think you did more work the first time you lifted the book or the second time you lifted the book? What do you think work means?

Work is the use of force to move an object.
Work is done by a force that acts in the same direction as the motion of an object. Work = Force • distance part of force doing work part of force not doing work object applied force direction of motion applied force object direction of motion

13.1 Work is the use of force to move an object. SIMUALATION
Determine how much work is done by lifting weights of different masses.

4.1 Vocab Work - The use of force to move an object over a distance.
Joule - The unit used to measure work; one joule of work is done when a force of one newton moves an object one meter.

Bell Work 2/23/11 What two factors do you need to know to calculate how much work was done in any situation? If you push very hard on an object but it does not move, have you done work? Explain, Tina lifted a box 3 m. She used a force of 25 N. How much work did Tina do on the box? Show your work!

Bell Work 2/22/10 If you apply a force of one Newton to a box as you push it for one meter. How many joules of work have you done? If you push a cart with a force of 50 N for 3 m, how much work will you do? Give an example of work that you have done. Name the object that was moved and the distance over which it moved.

Vocab 4.2 Potential energy - Stored energy, or the energy an object has due to its position. Calculating potential energy Gravitational Potential Energy = mass x gravitational acceleration x height GPE = mgh (on earth g = 9.8 m/s2)

MGH Example 1: What is the gravitational potential energy of a girl who has a mass of 40 kg and is standing on the edge of a diving board that is 5 m above the water?

MGH Example 2: An apple with a mass of 0
MGH Example 2: An apple with a mass of 0.1 kg is attached to a branch of an apple tree 4 m from the ground. How much gravitational potential energy does the apple have?

Kinetic Energy - The energy of motion; a moving object has the most kinetic energy at the point where it moves the fastest. Calculating Kinetic Energy Kinetic energy = mass x velocity2 2 KE = 0.5 m (v2)

KE Example 1: What is the kinetic energy of a girl who has a mass of 40 kg and a velocity of 3 m/s?

KE Example 2: A truck with a mass of 6000 kg is traveling north on a highway at a speed of 17 m/s. What is the kinetic energy of the truck?

Mechanical energy - A combination of the kinetic energy and potential energy an object has.
Calculating mechanical energy Mechanical Energy = Potential Energy + Kinetic Energy ME = PE + KE

ME Example: How much mechanical energy does a skateboarder have that has a potential energy of 200 joules due to his position at the top of a hill and a kinetic energy of 100 joules due to his motion?

Conservation of energy - A law stating that no matter how energy is transferred or transformed, all of the energy is still present in one form or another. Top of Ramp 100% PE 1 At the top of the ramp, the skater’s mechanical energy is equal to her potential energy because she has no velocity.

Halfway Down Ramp 50% KE PE 2
As the skater goes down the ramp, she loses height but gains speed. The potential energy she loses is equal to the kinetic energy she gains.

Bottom of Ramp 100% KE 3 As the skater speeds along the bottom of the ramp, all of the potential energy has changed to kinetic energy. Her mechanical energy remains unchanged.

Forms of Energy Thermal energy – the energy an object has due to the motion of its molecules Chemical energy – the energy stored in chemical bonds that hold chemical compounds together. Nuclear energy – the potential energy stored in the nucleus of an atom Electromagnetic energy – the energy associated with electrical and magnetic interactions

Bell Work 2/24/11 What is an Independent Variable? (IV) What is a Dependent Variable? (DV) What is a control? What are constants?

Bell Work – 3/2/11 Yelena holds a 10 kg ball over her head at a height of 25 m. What is the GPE of the ball? Quentin has a mass of 75 kg. When he rides his scooter at a velocity of 15 m/s, what is his kinetic energy? What is the formula for mechanical energy?

Bell Work 2/24/10 What is the law of conservation of energy?
Describe 3 different forms of energy.

Bell Work 3/3/11 A dumbbell weighing 20 kg is stored on a shelf 0.75 m high. How much gravitational potential energy does the dumbbell have? 2. How much work is done in lifting a 12 N hammer from the floor to a height of 2 m? 3. What is the mass of an apple sitting on top of a 12.5 m shelf that has a GPE of 25J?

Bell Work 3/4/11 Draw the following picture and label where the greatest and least PE and KE would be.

Science Fair 1. Problem 2. Independent Variable (IV)
Find your 2 favorite projects and write down the following information about each Title 1. Problem 2. Independent Variable (IV) 3. Dependent Variable (DV) 4. Summarize the experiment

What was your favorite science fair project yesterday?
Bell Work 2/26/10 What was your favorite science fair project yesterday? Write 3 sentences explaining the project and why it was your favorite project.

Bell Work 3/7/11 Match the correct term to each definition – write the definition and the term Terms – mechanical energy, potential energy, kinetic energy, work Stored energy The use of force to move an object a certain distance The energy of motion

The rate at which work is done.
13.3 Power is the rate at which work is done. power power watt The rate at which work is done. horsepower CHAPTER RESOURCES KEY CONCEPT SUMMARY

13.3 Power is the rate at which work is done. power watt watt The unit used to measure power; one watt is equal to one joule of work done in one second. horsepower CHAPTER RESOURCES KEY CONCEPT SUMMARY

13.3 Power is the rate at which work is done. power horsepower watt The unit of measurement for engines and motors; one horsepower equals 745 watts. horsepower CHAPTER RESOURCES KEY CONCEPT SUMMARY

Power can be calculated from work and time
Power = work time The unit of power is always a Watt (W)

Calculating power from work
Example: An Antarctic explorer uses 6000 J of work to pull his sled for 60 s. What power does he need?

Calculating power from work
Example 2: If a conveyor belt uses 10 J to move a piece of candy a distance of 3 m in 20 s, what is the conveyor belt’s power?

Calculating power from work
Example 3: An elevator uses a force of 1710 N to lift 3 people up 1 floor. Each floor is 4 m high. The elevator takes 4 s to lift the 3 people up 1 floor. What is the elevators power?

Calculating power from Energy
Power = Energy time The unit for power is Watts (W)

Calculating power from Energy
Example 1: A light bulb used 600 J of energy in 6 s. What is the power of the light bulb?

Calculating power from Energy
Example 2: A laptop computer uses 100 J every 2 seconds. How much power is needed to run the computer?

Calculating power from Energy
Example 3: The power needed to pump blood through your body is about 1.1 W. How much energy does your body use when pumping blood for 10 seconds?

Power is the rate at which work is done.
13.3 Power is the rate at which work is done. Power can be calculated from work and time. Power = Work time power watt horsepower Power can be calculated from energy and time. Power = Energy time CHAPTER RESOURCES Power is measured in watts (W) and sometimes horsepower (hp). SECTION OUTLINE

Bell work 3/8/11 How is power related to work?
What do you need to know to calculate how much energy a light bulb uses? Which takes more power: lighting a 50 W bulb, 75 W bulb, or 100 W bulb?

Chapter Resources Click on the items below to access resources on
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Bell Work 3/5/10 George is pushing a box across the floor at an angle and the box is moving only forward. Does all of George’s force do work on the box? Explain.

Bell Work 3/8/10 Get out the Power House Web Worksheet from last week and make sure you have the 4 questions on the front answered

Bell Work 3/9/10 Motion is a change in _______ over time
Jenna knows that a friend runs 100m in 8 s. She could use this to calculate her friend’s ________ Elena is riding her bicycle. She begins pedaling harder. Her ______ will increase. Speed in a specific direction is ______ Acceleration measures a change in _____ Latitude and longitude measure _____ You need to know ______ and _____ to measure speed

Article Review Title and author of article Who the article involves
Include the following in complete sentences Title and author of article Who the article involves What happened in the article Where the article took place When the article was written Why the article is important (2 sent.) How it relates to science (2 sent.)

Bell Work 3/11/10 1. Mary has a mass of 60 kg. When she rides her bike at a velocity of 4 m/s, what is his kinetic energy? KE = 1/2mv2. 2.The total mechanical energy of an object is 1500 J. If the kinetic energy of the object is 750 J, then the potential energy of the object is (ME = KE + PE) 3. Tyler applies a 150 N force for 15 s to slide a box 20 m across the floor. What is Tyler’s power? (P = W/t) (W = Fd)

Bell Work 3/12/10 Identify the action/reaction force pair involved when you catch a ball. Explain the difference between balanced forces and action/reaction forces. A man pushes on a wall with a force of 50 N. What are the size and the direction of the force that the wall exerts on the man?

What is your favorite type of ride to go on?
Bell Work 3/15/10 What is your favorite type of ride to go on? What is your favorite roller coaster and why?

Bell Work 3/16/10 What do you think the most difficult part will be when building your roller coaster? Why? What information would you like to find today in order to help you with the building of your roller coaster?

Bell Work 3/17/10 Happy St. Patrick’s Day! Try this trivia.
What colors are in the Ireland flag? What is the capital city of Ireland? How many leaves are on a lucky clover? What did St. Patrick drive out of Ireland? (snakes, a car, Leprechauns) Where do you find a pot of gold? What happens if you look away from a Leprechaun?

Green, Orange, White The colors in the flag have meaning: Green is for the North, orange is for the South and white is the Peace that binds them

Dublin, Ireland Dublin, Ireland is the third most visited capital city in Europe.

Four 4. According to the Guiness Book of World Records the most leaves ever found on a clover is 14.

Snakes According to the legend, St. Patrick drove all the snakes in Ireland out of the country and into the sea.

At the end of a rainbow If you are looking for a pot of gold go to the end of a rainbow and see if a Leprechaun has hidden one there.

He Disappears If you are lucky enough to find a leprechaun don’t take your eyes off of him, if you do he will disappear with his pot of gold.

Bell Work 3/18/10 What is the formula for speed?
Calculate the speed of a car traveling 300 meters in 20 seconds. Calculate the speed of your marble if it complete the 6 meter track in 12 seconds.

Bell Work 3/19/10 Draw and label the eight phases of the moon. Use the space science book if you need help.