2. ENERGY AND WORK Essential Question: How are energy, work and power related?

3. Types – – Kinetic – energy of motion – Mechanical – done by machines – Potential – stored energy (gravitational or elastic/flexed solids) – Chemical – found in the bonds between atoms Energy: The ability to do work

4. – Thermal – heat or internal kinetic energy – Sound – vibrations in matter carried on waves – Light – electromagnetic radiation – Electrical – moving and static electrical charges – Nuclear – found within the nucleus of atoms

5. Work – a force exerted during a distance. Work – a force exerted during a distance. W = F*d W = F*d Work and Energy… You must have energy to do work. Work and Energy… You must have energy to do work. Unit is Joules (J) Unit is Joules (J) Work

6. An acorn attempting to lift 230N (about 50 lbs.) one meter must pull with a force equal to the weight of the barbell. How much work has he done? W = F*d W = 230N * 1m W = 230 Mechanical Work 230N 1 m Unit? JJoules

7. 230N 2.5 m How much work to raise the bar over his head to the height of 2.5 m? * How much work to raise the bar over his head to the height of 2.5 m? * W= 230N*2.5m W= 230N*2.5m W= 575J W= 575J If we doubled the weight to 460N, what happens to the amount of work? If we doubled the weight to 460N, what happens to the amount of work? * If his arms were long enough! It would double as well! Directly Proportional

8. Work and Vectors (direction) Work is a vector, which means it has a direction. Work is a vector, which means it has a direction. Work can only be done if the force and distance directions are the same. Work can only be done if the force and distance directions are the same. F distance NO WORK DONE!!!

9. Amount of work done per the amount of time it takes to do it. Power Power = Work done (J) Time (s) Unit of power = J/s = 1 watt (W) 1 kilowatt (kW) = 1000 W

10. Essential Question: What is the relationship between potential energy and kinetic energy?

11. 1 st Law of Thermodynamics:1 st Law of Thermodynamics: –Energy can be changed from one form to another, but NOT destroyed. Change of energy: the final energy is equal to the beginning energy.Change of energy: the final energy is equal to the beginning energy. The ultimate source of ALL energy on Earth IS?The ultimate source of ALL energy on Earth IS? Law of Conservation of Energy

12. Gravitational Gravitational – PE g = mass * gravity * height – Higher an object = ____PE – Greater the mass = ____PE – Greater gravity = ____PE Elastic Elastic – PE elastic = weight x distance stretched – Greater the weight = ____PE – Greater the distance stretched = ____PE Potential Energy: Stored!

13. KE = ½ mass * velocity 2 KE = ½ mass * velocity 2 – The more massive the object = ____KE – The faster the object = ____KE – Why does velocity have a greater role in KE than mass? Kinetic Energy: Motion! The mass is cut in half but the velocity is squared!

14. The final energy is equal to the beginning energy. Law of Conservation of Energy Again!!!

15. KE i + PE i = KE f + PE f KE i + PE i = KE f + PE f In other words, the sum total of KE +PE before and after some kind of transformation MUST be equal. In other words, the sum total of KE +PE before and after some kind of transformation MUST be equal. Law of Conservation of Energy – YET AGAIN!!!

16. Entropy – a change of a useable form of energy into an unusable form… HEAT (thermal energy) Entropy – a change of a useable form of energy into an unusable form… HEAT (thermal energy) Whenever energy is “lost” it is ALWAYS converted into HEAT. Whenever energy is “lost” it is ALWAYS converted into HEAT. 2 nd Law of Thermodynamics - Entropy

17. Distance has to be in ______. Distance has to be in ______. Force has to be in _______. Force has to be in _______. – How do you change kg to N? Time has to be in ______. Time has to be in ______. Mass has to be in ________. Mass has to be in ________. Velocity has to be in _____. Velocity has to be in _____. How do you change W to kW? How do you change W to kW? Conversions seconds Newtons x10 meters kilograms m/s /10 3

18. The bow stores potential energy in its bent limbs when drawn. The bow stores potential energy in its bent limbs when drawn. This energy is transformed into kinetic energy as the arrow is released. This energy is transformed into kinetic energy as the arrow is released. PE of the bow = KE of arrow PE of the bow = KE of arrow PE & KE = work the archer had to use to draw the bow PE & KE = work the archer had to use to draw the bow Conservation of Energy: bow and arrow

19. Even though the arrow is now at rest (no KE) and the bow is not drawn (no PE), NO ENERGY HAS BEEN DESTROYED! The target did “Work” to the arrow by bringing it to rest with friction… Whenever energy is “lost” it is ALWAYS converted to HEAT. Where does the energy go???

20. What would happen to the depth of penetration if the arrow were moving faster? What would happen to the depth of penetration if the arrow were moving faster? What happens to the speed of the arrow when shot from a “stiffer” (harder to draw) bow? What happens to the speed of the arrow when shot from a “stiffer” (harder to draw) bow? What happens to the speed of the arrow if it weighs more? What happens to the speed of the arrow if it weighs more? What happens to the speed of the arrow if it is longer? (bow pushes it for a longer distance) What happens to the speed of the arrow if it is longer? (bow pushes it for a longer distance) Other thoughts

21. Equation Triangles F w dP w t mg PE h ½m KE v2v2 Work (J) Power (W) PE (J) KE (J) Work and energy have the same unit!