1. Chapter 5 “Energy” Physical Science Mrs. Nell’s Science Class

2. Energy Energy is the ability to cause change- it can cause something to move. Energy exists in many different forms, such as radiant, electrical, chemical, thermal, and nuclear.

3. Kinetic Energy Kinetic energy is energy in the form of motion. It depends on the mass and velocity of the moving object.

4. Mass A semi has great mass, so it has a great deal of kinetic energy.

5. Velocity Space debris has a great deal of kinetic energy because it is moving at a great velocity. Space debris punched a hole In Endeavour's radiator

6. Potential Energy Potential energy is stored energy. Potential energy depends on the position and the condition of the object.

7. Position A rock sitting on a cliff top has potential energy because of its position. The greater the height, the greater its potential energy. If it falls, its potential energy changes to kinetic energy.

8. Condition A rubber band that is pulled back has potential energy because of its condition.

9. Work Work is the transfer of energy through motion. When deciding whether work is being done, something has to move, and the motion must be in the same direction as the applied force.

10. Joules Work, like energy, is measured in joules. It is named for British scientist, James Prescott Joule.

11. Calculating Work The amount of work done depends on two things: The amount of force exerted The distance over which the force is applied

12. Practice Problem #1 How much work is done by a person who uses a force of 27.5N to move a grocery buggy 12.3 meters? W = F x d = (27.5N) (12.3m) = 338.25 J

13. Practice Problem #2 55000 J of work is done to move a rock 25 m. How much force was applied? F = W = 55,000J = ? d 25m Answer F = 2200N

14. Practice Problem #3 You and 3 friends apply a combined force of 489.5N to push a piano. The amount of work done is 1762.2J. What distance did the piano move? You need to rearrange the work formula to look for distance: d= W = 1762.2J = F 489.5N Answer d = 3.6m

15. More Practice Problems 1. If it took a bulldozer 567.6 joules of work to push a mound of dirt 30.5 meters, how much force did the bulldozer have to apply? 2.A young boy applied a force of 2,550 newtons on his St. Bernard dog who is sitting on the boy's tennis shoes. He was unable to move the dog. How much work did he do trying to push the dog? 3. If a weight lifter raises a barbell with a mass of 125.7 grams doing 5,023 joules of work, what distance did he move the barbells? (HINT: Remember that you need a force, not a mass. You must first calculate the force in order to complete your solution. )

16. Conservation of Energy If you think about the motion of a swing, the energy changes as the swing moves. At the highest point, the mechanical energy is entirely potential. As the swing falls it gains kinetic energy and potential energy decreases. The law of conservation of energy states that energy may change form, but it cannot be created or destroyed under ordinary conditions.

17. Where does the energy go? We know that the swing eventually comes to a stop. Friction and air resistance act on the swing and rider, causing some of the mechanical energy of the swing to change to thermal energy or heat.

18. The Human Body When we eat food, our body chemically changes the food into molecules to be used a fuel. Some of the potential energy stored in your body is used to maintain a nearly constant body temperature. Some of the heat is also given off by the body to its surroundings.

19. Burning Calories In 1 hour, a person of medium body frame will burn off… 84 calories sitting 98 calories eating 112 calories standing 210 calories walking420 calories playing tennis850 calories running 56 calories sleeping 600 calories biking fast

20. Temperature & Heat Temperature is a measure of the average kinetic energy of the particles in a sample of matter. As the particles move faster, and their average kinetic energy becomes greater, the temperature rises. As the particles move slower, their average kinetic energy decreases. The particles in a cup of hot coffee are moving very fast The particles in a cup of tea are moving slowly

21. Thermal Energy Thermal energy is the total energy of the particles in a material. The total includes both kinetic and potential energy. The more mass a material has, the more particles it has- so the more thermal energy it has.

22. Heat Heat is thermal energy that flows from something with a higher temperature to something with a lower temperature. In most cases, heat flows from warmer to cooler materials. Like work, heat is measured in joules and involves transfer of energy.

23. Thermal Pollution Thermal pollution occurs when waste heat significantly changes the temperature of the environment. It occurs when water that is used to cool buildings and equipment is dumped into rivers, lakes, and oceans. The added heat lowers the dissolved oxygen content and can kill plants and animals.

24. Cooling Towers Cooling towers can be used to cool water by fans or evaporation. These towers are effective, but expensive. Some people think we should use this warm water to heat greenhouses or other buildings.

25. Measuring Thermal Energy Different materials need different amounts of heat to cause a change in their temperatures. The materials have different specific heats. Specific heat is the amount of energy it takes to raise the temperature of 1 kg of the material 1 kelvin. MATERIALSPECIFIC HEAT (J/kg°C) Water4184 Aluminum900 Steel470ç Silver235 Oil1900 Concrete880 Glass800 Gold129 Wood2500 Specific Heat is also measured in [J/(kg * K)]

26. Heat Absorption Water has a high specific heat. It heats up much slower than other materials. Silver, which has a low specific heat, heats up very quickly.

27. Low Specific Heat Sand has a specific heat of 664 [J/(kg*K)]. This is why sandy beaches heat up quickly on a sunny day.

28. Calculating Thermal Changes Specific heat can be used to determine changes in thermal energy. Change in thermal energy = mass x change in temperature x specific heat ΔT = T final – T initial Q= m x ΔT x C

29. Practice Problem #1 Which of the substances listed in the table would heat up more quickly if an equal amount of heat energy were applied to all of the substances at the same time? Explain your answer. Answer: Gold Which of the substances listed in the table would you choose as the best insulator? Explain your answer. Answer: Water MATERIALSPECIFIC HEAT (J/kg°C) Water4184 Aluminum900 Steel470 Silver235 Oil1900 Concrete880 Glass800 Gold129 Wood2500

30. Practice Problem #2 How much energy is required to heat 35 grams of gold from 10 to 50°C? Answer: Q =.035 x 40 x 129 = 180.6 J MATERIALSPECIFIC HEAT (J/kg°C) Water4184 Aluminum900 Steel470 Silver235 Oil1900 Concrete880 Glass800 Gold129 Wood2500

31. Practice Problem #3 What is the change in temperature for a 2-kilogram mass of water that loses 8,500 joules of energy? Answer: -8500 = 2 x ΔT x 4184 -8500 = ΔT x 8368 -8500 = ΔT 8368 -1.02° C = ΔT MATERIALSPECIFIC HEAT (J/kg°C) Water4184 Aluminum900 Steel470 Silver235 Oil1900 Concrete880 Glass800 Gold129 Wood2500

32. Practice Problem #4 What is the specific heat of a material that gains 600 joules of energy when a 0.25-kilogram object increases in temperature by 3°C? What is this material? Answer: 600=.25 x 3 x C 600 = C.75 800 = C The material is glass MATERIALSPECIFIC HEAT (J/kg°C) Water4184 Aluminum900 Steel470 Silver235 Oil1900 Concrete880 Glass800 Gold129 Wood2500

33. Practice Problem #5 When 1,500 joules of energy is lost from a 0.12-kilogram object, the temperature decreases from 45°C to 40°C. What is the specific heat of this object? Of what material is the object made? MATERIALSPECIFIC HEAT (J/kg°C) Water4184 Aluminum900 Steel470 Silver235 Oil1900 Concrete880 Glass800 Gold129 Wood2500 Answer: -1500=.12 x -5 x C -1500= C -.6 2500 = C The material is wood

34. Practice Problem #6 What is the mass of a block of concrete that gains 52,800 joules of energy when its temperature is increased by 5°C? MATERIALSPECIFIC HEAT (J/kg°C) Water4184 Aluminum900 Steel470 Silver235 Oil1900 Concrete880 Glass800 Gold129 Wood2500 52800 = m x 5 x 880 52800 = m x 4400 52800 = m 4400 12 kg = m