1. Ch 14, 15, 16 Work, Power, Energy, and Heat

2. Work – transfer of energy through motion a. Force must be exerted through a distance Ch 14 WORK AND POWER

3. b. Amount of Work depends on: –1. Amount of applied Force –2. Distance over which the force is applied Work F d

4. c. W=Fd (Force multiplied by distance) d. Unit is the Joule (1J = 1Nm) Work F d

5. e. In order for work to be done: –1. Something has to move –2. Motion must be in the direction of the force

6. How much work is done when a car is pushed with 600 N of force for a distance of 50m?

7. How far will a ball roll if 17J of work was done to push it with 2 N of force?

8. Power – rate of doing work a. To increase Power: –1. increase work done –2. do work in less time

9. b. P=W/t (Work divided by time) c. SI unit is Watt (1W=1J/s) d. common unit is horsepower (1hp=746W) Work P t

10. How much power is needed to do 40 Joules of work in 5 seconds?

11. How long will it take to do generate 70 Watts of power if I do 4900 Joules of work? How much power will I need if I want to do the same amount of work in half the time?

12. Reference table check Work F d P t Fd P t

13. You exert a vertical force of 72 N to lift a box a height of 1 meter in a time of 2 seconds. How much power is used to lift the box?

14. Star questions True or False –Decreasing the amount of time it takes to do work, increases the power –Motion must occur in order for work to be done

15. Ch 15-Energy Energy is the ability of an object to cause change Basic unit is the Joule (J) =Nm

16. Forms of energy 1. Mechanical = PE+KE 2. Thermal = heat 3. Chemical = wood, gasoline 4. Electrical = lightning, batteries 5. Electromagnetic = visible light, x-rays 6. Nuclear = fission, fusion

17. Kinetic Energy – energy in the form of motion a. Greater mass, more KE b. Greater velocity, more KE

18. A 20-kg kid slides down a slide at a velocity of 2 m/s. What is the kinetic energy of the kid?

19. Potential Energy – stored energy a. Amount depends on: 1. Position 2. Shape

20. Types of PE: 1. Gravitational – related to height above Earth’s surface a. Higher up, more PE b. Greater mass, more PE

21. 2. Elastic – object that is stretched or compressed

22. 3. Chemical – found in food or fuels

23. PE=mgh=F g h SI unit is Joule=J=Nm PE mg h

24. A potted plant on a 2.5 m high window sill has a mass of 3-kg. What is the potential energy of the plant?

25. A man weighing 950N stands at the top of 30m cliff. What is the man’s potential energy?

26. 3 people of equal mass climb the mt using different paths. Which path shows the person gaining the most PE?

27. Roller coaster max height PE speed ME

28. Energy Conversion – process of changing energy from one form to another

30. Law of Conservation of Energy states that matter cannot be created nor destroyed

32. STAR Questions List the 6 forms of energy –Mechanical, chemical, electromagnetic, thermal, electrical, nuclear Work depends on what 2 things? –Distance and force KE, chemical PE, elastic PE or gravitational PE? –Bouncing ball –Rock at edge of cliff –Glass of Orange Juice –Car battery –Compressed spring KE Gravitational PE Chemical PE Elastic PE

33. 30 o C 90 o C Heat =energy that flows from higher temps to lower temps Ch 16-HEAT What will happen to the temperature in the beakers over time?

34. Temperature –measure of average KE of the particle in a sample of matter –a. Increase temp = greater KE –b. Decrease temp = lower KE –c. Absolute Zero=0K= KE of all particles cease

35. Thermal Energy – the total energy of the particles in a material (both KE and PE) a. More mass at the same temp means greater thermal energy

36. KE of 3? TE of 3? 200g 400g 50 o C 70 o C

37. Thermal Expansion & Contraction a. Hot temps cause materials to expand b. Cold temps cause materials to contract

38. Specific Heat (C) – amount of energy needed to raise the temp of 1g of a material by 1 o C Think of it as “resistance to temperature change” The higher the c, the harder it is the change the temp.

39. An iron spoon and a silver spoon have the same mass. Which becomes hotter when both are left in hot chocolate for one minute? Pg 476 for c values

40. Why does a piece of steel heat up more than an equal mass of wood when both absorb the same energy? The metal has a lower specific heat than the wood, so its temp increases more as thermal energy is absorbed

41. Which substance will have the greatest increase in temp when equal masses absorb equal amounts of thermal energy? Water (4.18 J/g o C) Ethyl alcohol (2.43 J/g o C ) Ammonia gas (2.1 J/g o C ) Aluminum (0.90 J/g o C ) Lead (0.46 J/g o C )

42. Answer : A

43. The same energy was added to each sample. Which material has the highest specific heat? Al, b/c Temp rises the least for a given amt energy added. Smaller ΔT means a larger specific heat

44. It is impossible to build a machine that does nothing but convert thermal energy into useful work. no machine can be 100% efficient, why not? Energy Efficiency

45. Thanks Cambridge Physics Outlet for amazing graphics!

46. Conduction – transfer of energy through matter by direct contact of particles a. Energy is transferred when particles moving at different speeds collide b. Occurs in solids, liquids, and gases –1. Solids conduct better

47. Convection – transfer of energy by the movement of matter a. Fluid – anything that flows b. Occurs in liquids & gases

48. Radiation –transfer of energy in form of waves a. Shiny materials reflect radiant energy b. Dull materials absorb c. Darker colors absorb more d. Lighter colors absorb less

49. STAR Questions Decrease temperatures = ___________ KE Decreased Hot temperatures cause materials to ______ Expand The higher the C-specific heat, the _________ it is to change the temp Harder Dull materials ___________ radiant energy Absorb Lighter colors reflect ___________ radiant energy less