1. Chapter 15 – Energy

2. Work is done when a force moves an object through a distance
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. - The energy to do this comes from your muscles
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. Recall, work is done when a force moves an object through a distance
15.1 Energy and Its Forms
Recall, work is done when a force moves an object through a distance
What is Newton’s 2nd Law?
Substitute a:
A kinematics equation:
Solve for a:
Rearrange:
Kinetic Energy
Work

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

6. - Doubling the mass the kinetic energy Doubles
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. Positive work must be done to raise the hammer from the ground.
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. - The baby works to get to the top of the diving board (F x d)
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. - mass (m) is in kilograms
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
Elastic Potential Energy – The potential energy of an object that is stretched or compressed
- Something is considered elastic if it springs back to its original shape after being stretched or compressed

14. There are 6 major forms of energy
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. It is the sum of an object’s potential and kinetic energy
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. Chemical Energy – The energy stored in chemical bonds
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. Electrical Energy – energy associated with electric charge
15.1 Energy and Its Forms
Electrical Energy – energy associated with electric charge
Electric charges can exert forces that do work

19. The sun radiates electromagnetic waves
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. Nuclear Energy – The energy stored in atomic nuclei
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. Energy conversion – energy can be converted from one form into another
15.2 Energy Conversion and Conservation
Energy conversion – energy can be converted from one form into another
Gravitational potential energy to kinetic energy

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

23. Energy conversion – energy can be converted from one form into another
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. Law of Conservation of Energy – energy cannot be created or destroyed
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. Mechanical Energy – The sum of an object’s total KE and total PE
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. (KE + PE)beginning = (KE + PE)end
15.2 Energy Conversion and Conservation
Energy Conversions Calculations
Law of Conservation of Mechanical Energy
(ignore friction!)
(KE + PE)beginning = (KE + PE)end

34. Page 458 Math Skills and Math Practice
15.2 Energy Conversion and Conservation
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 1
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?
Example 2
Page 458 Math Skills and Math Practice
Read Page 459 on E = mc2

35. Questions to answer from Roller Coasters video
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.