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3. Work: done ONLY when a force is applied to an object, and the object moves IN THE SAME DIRECTION OF THE APPLIED FORCE Work is calculated by multiplying the force by the distance over which the force is applied Work = force x distance W = F x d 3

4. The SI unit for work is Joules (J) Work is expressed as F x d (Newtons x meters) So, 1 N x 1 m = 1 J = 1 kg x m 2 /s 2 4

5. Work is ZERO when an object is not moving If you are trying to push a stalled car, you might exert a lot of force, but are unable to move it No work is done If you move it, even a little, Work is done 5

6. Power: the rate at which work is done, or how much work is done in a given amount of time Power = work/time P = W/t The SI unit for power is watt (W) One watt is the amount of power needed to do one joule of work in one second 6

7. BE CAREFUL! The W for work is not italicized The W for watt is italicized Science 360: Hockey Work, Energy and Power 7

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9. Energy is ALL around us and exists in many forms It is the ability to do work Whenever work is done, energy is transformed or transferred from one system to another 9

10. The SI unit for energy is Joules (J) The same units as work since work is only measured when you use energy to do it There are two kinds of energy – potential and kinetic 10

11. Potential Energy (PE): stored energy, or the energy of position 11

12. Gravitational Potential Energy (GPE): energy due to an object’s height above ground Depends on mass and height If you drop two apples with different masses from the same height, the HEAVIER apple will have more GPE than the lighter apple GPE = mass x free-fall acceleration x height GPE = mgh GPE = m(9.8 m/s 2 )h 12

13. Kinetic Energy (KE): energy of motion – the energy an object has because it is moving Once an object begins to move, it has the ability to do work The kinetic energy depends on the mass of the object, and the rate of acceleration 13

14. An apple that is falling at 10 m/s can do more work than an apple that is falling at 1 m/s KE = ½ x mass x speed squared KE = 1/2mv 2 14

15. Depends more on speed than it does on mass A small change in speed produces a large change in kinetic energy A speeding car will do more damage because it has higher kinetic energy Atoms and molecules are always moving, so they have kinetic energy 15

16. All motion involves energy All forms of energy have both a kinetic and potential type 16

17. Mechanical Energy: the amount of work an object can do because of its kinetic and potential energies combined A car moving, a ball that has been thrown, a person falling 17

18. Chemical Energy Energy that is released or absorbed by the rearrangement of bonds between atoms Reactions that release energy decrease potential energy Reactions that require energy increase potential energy Solar Virtually all energy on this planet comes from the sun Through photosynthesis, plants convert energy from sunlight into chemical energy This energy is transferred through the food chain when consumers eat plants! 18

19. Nuclear Energy: the movement of particles in the nucleus of an atom Fission: a large nucleus splitting in to two smaller nuclei Fusion: light atomic nuclei combining to form a heavier one This is how the sun gets energy! 19

20. Electrical Energy: energy resulting from the movement of electrons across a circuit Thermal Energy: the sum of kinetic energy in all the particles of an object Heat energy The higher the temperature, the more thermal energy The larger something it, the more thermal energy it has 20

21. Light Energy: movement of “packets of energy” called photons Cause a vibration in charged particles Also called electromagnetic energy Anything you can see and X rays, UV rays, and infrared waves Sound Energy: vibrations travelling through the medium of the sound Sound requires a medium (something to travel through) Like a wave 21

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23. Energy readily changes from one form to another, but the total amount of energy always remains the same 23

24. Potential energy can become kinetic energy As a car on the top of a hill rolls down the hill, the energy changes from potential energy to kinetic energy When the car reaches the lowest point, there is no potential energy Kinetic energy can become potential energy At the bottom of the hill, the kinetic energy can take the car up the next hill; the car slows down and most of the energy turns back into potential energy 24

25. The change of kinetic to potential energy and vice versa isn’t always complete If so, balls would always bounce to the same height and roller coasters would never stop gliding Some mechanical energy (KE + PE) will change to other forms of energy Some changes to elastic potential energy Some is released as a sound from the plastic compressing The air around the ball gets warmer 25

26. Energy cannot be created or destroyed, it can only change forms 26

27. Thermodynamics describes energy conservation Energy can be transferred as work or heat In any system, the change in energy equals the energy transferred as work and as heat This form of the law of energy conservation is known as the first law of thermodynamics 27

28. Energy is everywhere, so scientists often focus on a small area or small number of objects These boundaries define a system Open System: a system in which energy and matter are exchanged with the surroundings Closed System: energy is exchanged, but not matter Isolated System: no energy or matter is exchanged 28

29. Machines help us do work However, only a portion of the work done by any machine is useful work – meaning work that the machine is designed to do There is a difference between the total work and the useful work done by a machine Some work is done in the addition of heat, or noises created by the machine but it isn’t “useful” because it is not what the machine is intended for 29

30. Efficiency: a quantity, usually expressed as a percentage, that measures the ratio of useful work to work output Efficiency = useful work output/work input Multiply the answer by 100 to get the percentage 30

31. Perpetual Motion Machine: designed to keep moving without the input of energy This could happen only in the absence of friction and air resistance, a condition that does not exist in this world Machines require an input of energy because some energy “leaks” from the system 31