Chapter 15 – Energy

1. Chapter 15 – Energy

2. 15.1 Energy and Its Forms Work is done when a force moves an object through a distance Energy – The ability to do work In other words, energy is transferred by moving an object through a distance. So, work is a transfer of energy

3. 15.1 Energy and Its Forms Think about the energy needed to carry your backpack up a flight of stairs - You do work by lifting the backpack against gravity (requires energy) - The energy to do this comes from your muscles - Your muscles get the energy from the food we eat - The energy in the plants you eat, or animals you eat that ate the plants, comes from the sun

4. 15.1 Energy and Its Forms A kinematics equation: Substitute a: Kinetic Energy Work Recall, work is done when a force moves an object through a distance What is Newton’s 2nd Law? Solve for a: Rearrange:

5. 15.1 Energy and Its Forms An object in motion can apply a force to something and in turn do work to that object (it has energy– the ability to do work) Kinetic Energy – energy an object has because it is in motion The moving bowling ball can do work on the pins What is meant by kinetic energy? Applying a force to an object through some distance sets that object into motion The unit of KE is the joule

6. 15.1 Energy and Its Forms - Doubling the mass the kinetic energy Doubles - Doubling the speed the kinetic energy Quadruples

7. 15.1 Energy and Its Forms • Page 448 • Read Math Skills • Do Math Practice

8. 15.1 Energy and Its Forms Potential Energy – Energy that is stored as a result of position or shape

9. 15.1 Energy and Its Forms Positive work must be done to raise the hammer from the ground. When raised to a height and dropped, gravity can do work on the hammer As it falls, the hammer will gain kinetic energy, and be able to do work on the pile The hammer, when raised has the potential to do work

10. 15.1 Energy and Its Forms

11. 15.1 Energy and Its Forms Gravitational Potential Energy – Potential energy that depends on an object’s height - The baby works to get to the top of the diving board (F x d) - The work done is dependent on the mass of the baby and the height the baby climbed - That work becomes Gravitational Potential Energy

12. 15.1 Energy and Its Forms Gravitational Potential Energy depends on mass, height, and the acceleration due to gravity (g) - mass (m) is in kilograms - g is 9.8 m/s2 - height (h) is in meters - always measured relative to an arbitrary reference level

13. 15.1 Energy and Its Forms - Something is considered elastic if it springs back to its original shape after being stretched or compressed Elastic Potential Energy – The potential energy of an object that is stretched or compressed

14. 15.1 Energy and Its Forms There are 6 major forms of energy - Mechanical Energy - Thermal Energy - Chemical Energy - Electrical Energy - Electromagnetic Energy - Nuclear Energy

15. 15.1 Energy and Its Forms Mechanical Energy – the energy associated with motion and the position of everyday objects. It is the sum of an object’s potential and kinetic energy

16. 15.1 Energy and Its Forms Thermal Energy – The total potential and kinetic energy of all the atoms and molecules in an object Recall the kinetic theory of matter – atoms and molecules are always in motion

17. 15.1 Energy and Its Forms Chemical Energy – The energy stored in chemical bonds When bonds are broken, the released energy can do work

18. 15.1 Energy and Its Forms Electrical Energy – energy associated with electric charge Electric charges can exert forces that do work

19. 15.1 Energy and Its Forms Electromagnetic Energy – a form of energy that travels through space in the form of waves The sun radiates electromagnetic waves

20. 15.1 Energy and Its Forms Nuclear Energy – The energy stored in atomic nuclei Fission and Fusion are two processes that release nuclear energy

21. 15.2 Energy Conversion and Conservation Energy conversion – energy can be converted from one form into another Gravitational potential energy to kinetic energy

22. 15.2 Energy Conversion and Conservation Energy conversion – energy can be converted from one form into another Elastic potential energy to kinetic energy

23. 15.2 Energy Conversion and Conservation Energy conversion – energy can be converted from one form into another Potential energy to electric energy and electromagnetic energy

24. 15.2 Energy Conversion and Conservation Law of Conservation of Energy – energy cannot be created or destroyed

25. 15.2 Energy Conversion and Conservation Energy Conversions Pendulums

26. 15.2 Energy Conversion and Conservation

27. 15.2 Energy Conversion and Conservation

28. 15.2 Energy Conversion and Conservation

29. 15.2 Energy Conversion and Conservation

30. 15.2 Energy Conversion and Conservation Energy Conversions Pole Vault

31. 15.2 Energy Conversion and Conservation

32. 15.2 Energy Conversion and Conservation Energy Conversions Mechanical Energy – The sum of an object’s total KE and total PE Mechanical Energy = KE + PE

33. 15.2 Energy Conversion and Conservation Energy Conversions Calculations Law of Conservation of Mechanical Energy (ignore friction!) (KE + PE)beginning = (KE + PE)end

34. 15.2 Energy Conversion and Conservation Example 1 If you throw a baseball straight up with a speed of 5 m/s, what will be the speed of the ball when it comes back to your hand. Ignore air resistance? Example 2 A 1000 kg car is coasting at 10 m/s toward a hill that is 10 m high. Will the car make it to the top of the hill if the driver does not step on the gas pedal? Page 458 Math Skills and Math Practice Read Page 459 on E = mc2

35. 15.2 Energy Conversion and Conservation • Questions to answer from Roller Coasters video • How does the roller coaster get to the top of the first hill? • How does the roller coaster continue to move after the first hill? • When does the roller coaster have the most potential energy? • What happen’s to the roller coaster’s potential energy as it goes down a hill? • Why are the frames of modern roller coasters made out of steel, instead of the wooden frames that were once used?

36. 15.2 Energy Resources

37. 15.2 Energy Conversion and Conservation Energy Conversions The gravitational potential energy of an object is converted to kinetic energy of motion as the object falls (roller coaster) The elastic potential energy of a spring is converted to kinetic energy of motion as the spring is restored (screen door)

38. HEAT

39. HEAT • Conduction- transfer of thermal energy with no overall transfer of matter • Occurs within a material or between materials that are touching • Due to particle collisions • NEWTON’S CRADLE

40. CONDUCTION

41. Conduction in gases • Slower than in liquids or solids. • Why? • Gas particles are further apart and therefore collide less frequently

42. Why are metals good condcutors? • Some electrons move freely in metals • These collide with each other and other atoms to transfer thermal energy

43. Thermal Conductors • Conduct thermal energy well • What are pots and pans made of? • Why do tile floors feel colder than carpet or wood?

44. Thermal Insulators • Conduct thermal energy poorly • Air- very good insulator- double paned windows • What are coolers made of?

45. CONVECTION • Transfer of energy when particles of fluids move from one place to another • We all know that hot air…… • RISES • Why? • Becomes less dense as particles gain KE and spread out. • Therefore, cool air sinks

46. CONVECTION

47. Convection Currents • The cycling of hot air rising and cool air sinking • Important in ocean currents, weather systems, movements of hot rocks in the Earth

49. RADIATION • Transfer of energy by waves moving through space • What do you feel when you stand by a hot stove without touching it? • What do you feel when you go outside on a sunny day? • When temperature increases rate of radiation increases.