Motion and Forces

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Motion and Forces

• Work and Energy
• Chapter 4

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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.

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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?

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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
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13.1
Work is the use of force to move an object.
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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.

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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!

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Bell Work 2/22/10

1. 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.

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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)

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• 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?

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• 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?

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• 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)

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• 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?

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• 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?

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• 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

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• 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?

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• 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.

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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

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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?

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Bell Work 2/24/10

1. What is the law of conservation of energy?
2. Describe 3 different forms of energy.

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Bell Work 3/7/11

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

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Science Fair

• Find your 3 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

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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.

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Bell Work 3/8/11

• 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

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power
13.3
Power is the rate at which work is done.
power
watt
horsepower
The rate at which work is done.
CHAPTER RESOURCES
KEY CONCEPT SUMMARY
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watt
13.3
Power is the rate at which work is done.
power
watt
horsepower
The unit used to measure power one watt is equal
to one joule of work done in one second.
CHAPTER RESOURCES
KEY CONCEPT SUMMARY
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horsepower
13.3
Power is the rate at which work is done.
power
watt
horsepower
The unit of measurement for engines and motors
one horsepower equals 745 watts.
CHAPTER RESOURCES
KEY CONCEPT SUMMARY
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Power can be calculated from work and time

• Power work
• time
• The unit of power is always a Watt (W)

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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?

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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 belts power?

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

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Calculating power from Energy

• Power Energy
• time
• The unit for power is Watts (W)

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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?

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Calculating power from Energy

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

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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?

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Power is the rate at which work is done.
13.3
Power can be calculated from work and time.
power
watt
horsepower
Power can be calculated from energy and time.
CHAPTER RESOURCES
Power is measured in watts (W) and sometimes
horsepower (hp).
SECTION OUTLINE
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Bell work 3/9/11

1. 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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BACK TO CHAPTER
41
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 Georges force do work on the box? Explain.

42
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

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Bell Work 3/9/10

1. 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 friends ________
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

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Article Review

• 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.)

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Bell Work 3/10/11

• 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 Tylers
  power? (P W/t) (W Fd)

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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?

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Bell Work 3/15/10

1. What is your favorite type of ride to go on?
2. What is your favorite roller coaster and why?

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Bell Work 3/16/10

1. What do you think the most difficult part will be
   when building your roller coaster? Why?
2. What information would you like to find today in
   order to help you with the building of your
   roller coaster?

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Bell Work 3/17/10

• Happy St. Patricks 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?

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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

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Dublin, Ireland

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

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Four

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

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Snakes

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

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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.

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He Disappears

• If you are lucky enough to find a leprechaun
  dont take your eyes off of him, if you do he
  will disappear with his pot of gold.

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Bell Work 3/18/10

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

57
Bell Work 3/19/10

• Draw and label the eight phases of the moon. Use
  the space science book if you need help.