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. 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 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 2/22/10 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.

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/s 2 )

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 velocity 2 2 KE = 0.5 m (v 2 )

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 2 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?

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

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

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

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