Motion and Forces Work and Energy Chapter 4. Bell Work 2/18/10 Write each statement, then decide if the statement is true or false, if false correct it.

Motion and Forces

Work and Energy

Chapter 4

Bell Work 2/18/10Write each statement, then decide if the

statement is true or false, if false correct it.

1. An object has acceleration if its velocity is changing.

2. Force is measured in joules.

3. Gravity is a force.

How do you work?

1. Do you think you did more work the first time you lifted the book or the second time you lifted the book?

2. What do you think work means?

Work is done by a force that acts in the same direction as the motion of an object.Work = Force • distance

Work is the use of force to move an object.

applied force

object

direction of motion

part of force doing work

part of force not doing work

object

applied force

direction of motion

Work is the use of force to move an object.13.113.1

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 2/19/10

1. What two factors do you need to know to calculate how much work was done in any situation?

2. If you push very hard on an object but it does not move, have you done work? Explain,

3. 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 2/22/101. 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?

2. If you push a cart with a force of 50 N for 3 m, how much work will you do?

3. Give an example of work that you have done. Name the object that was moved and the distance over which it moved.

Vocab 4.2Potential 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 0.1 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 Ramp100%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 Ramp2

50%KE

50%PE

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 – 2/23/10 1. When Roger kicks a football, the football gains

mechanical energy because Roger does ______ on the football.

2. Yelena holds a 5 kg ball over her head at a height of 2 m. What is the GPE of the ball?

3. Quentin has a mass of 50 kg. When he rides his scooter at a velocity of 3 m/s, what is his kinetic energy?

4. What is the formula for mechanical energy?

Bell Work 2/24/10

1. What is the law of conservation of energy?

2. Describe 3 different forms of energy.

Bell Work 2/25/10

Draw the following picture and label where the greatest and least PE and KE would be.

Science Fair

Find your 3 favorite projects and write down the following information about each

Title

1. Problem2. Independent Variable (IV)3. Dependent Variable (DV)4. Summarize the experiment

Bell Work 2/26/10

1. What was your favorite science fair project yesterday?

2. Write 3 sentences explaining the project and why it was your favorite project.

Bell Work 3/1/10Match the correct term to each definition –

write the definition and the term

Terms – mechanical energy, potential energy, kinetic energy, work

1. Stored energy

2. The use of force to move an object a certain distance

3. The energy of motion

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?


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?


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 8 s to lift the 3 people up 2 floors. What is the elevators power?

Calculating power from Energy

Power = Energy time

The unit for power is Watts (W)


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


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


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 can be calculated from work and time.

SECTIONOUTLINESECTIONOUTLINE

Power is the rate at which work is done.

watt

power

horsepower

Power = Worktime

Power can be calculated from energy and time.

Power = Energytime

Power is measured in watts (W) and sometimes horsepower (hp).

13.313.3

CHAPTERRESOURCESCHAPTERRESOURCES

Bell work 3/2/101. How is power related to work?

2. What do you need to know to calculate how much energy a light bulb uses?

3. Which takes more power: lighting a 50 W bulb, 75 W bulb, or 100 W bulb?

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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 3/9/101. Motion is a change in _______ over time

2. Jenna knows that a friend runs 100m in 8 s. She could use this to calculate her friend’s ________

3. Elena is riding her bicycle. She begins pedaling harder. Her ______ will increase.

4. Speed in a specific direction is ______

5. Acceleration measures a change in _____

6. Latitude and longitude measure _____

7. You need to know ______ and _____ to measure speed

Article ReviewInclude 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 3/11/101. 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 3/11/101. If you traveled 200 m in 50 seconds

what is your speed?

2. A car traveling at 40 m/s slows down to a complete stop in 10 seconds. What is the acceleration of the car?

3. A sprinter starts a race at 5 m/s then 10 seconds later he finishes the race at 10 m/s. What is the acceleration of the runner?

Bell Work 3/12/10

1. Identify the action/reaction force pair involved when you catch a ball.

2. Explain the difference between balanced forces and action/reaction forces.

3. 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?

Motion and Forces Work and Energy Chapter 4. Bell Work 2/18/10 Write each statement, then decide if the statement is true or false, if false correct it.

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