1. Warm-Up: How much power is required to lift a 50N box 3 m in 5 s?
A box has a mass of 5kg. What is its weight?
Describe in your own words what power is. (USE SCIENTIFIC DEFINITION)

2. Warm-Up: What is the equation for power?
A box has a mass of 5kg. What is its weight?
Describe in your own words what power is. (USE SCIENTIFIC DEFINITION)

3. Work and Energy: Forms and Changes

4. Energy The ability to do work
It is like the “Currency” for performing work. To do 100 J of work, you must expend 100 J of energy
Energy

5. Energy Energy is all around you: You use energy when you:
Light
Heat
Wind
You use energy when you:
hit a softball
lift your book bag
digest food
Every change that occurs—large or small—involves energy

6. Changes Require Energy
When something is able to change its environment or itself, it has energy
Anything that causes change must have energy
You use energy to arrange your hair to look the way you want it to
You also use energy when you walk down the halls of your school between classes or eat your lunch

7. Nature of Energy What is energy? Energy- the ability to do work
If an object or organism does work the object or organism uses energy
Whenever you do work you transfer energy from one thing to another

8. Nature of Energy
Because of the direct connection between energy and work, energy is measured in the same unit as work: joules (J)
In addition to using energy to do work, objects gain energy because work is being done on them

9. ANSWER QUESTION 9 ON YOUR CATAPULT WS
IN YOUR OWN WORDS
ANSWER QUESTION 9 ON YOUR CATAPULT WS

10. Forms of Energy
Some examples of different forms of energy are:
Thermal (heat)
Chemical
Electromagnetic
Nuclear
Mechanical
If you have $100, you could store it in a variety of forms—cash in your wallet, a bank account, or coins
Regardless of its form, money is money, and the same goes for energy in that these are only different forms of the same thing

11. States of Energy
The most common energy conversion is the conversion between potential and kinetic energy
All forms of energy can be in either of two states:
Potential
Kinetic

12. Kinetic Energy Kinetic energy- the energy of motion
Depends on both mass and velocity
The faster an object moves, the more kinetic energy it has
The greater the mass of a moving object, the more kinetic energy it has
KE = Ek = mass x velocity2 2
What has a greater effect on kinetic energy, mass or velocity? Why?

13. Potential Energy Even motionless objects have energy
Potential energy- stored energy due to interactions between objects
If the apple stays in the tree, the energy will remain stored
If the apple falls, that stored energy is converted to kinetic energy

14. When did you use PE?
Explain how your catapult utilized PE.

15. When did you use KE?
Explain how your catapult utilized KE.

16. Common forms of Potential Energy
You will each be given one of three common forms of PE.
Read your slide of information and write a 1 sentence summary in your notebook.
Share your 1-sentence summaries with other classmates.
You should write down their 1-sentence summary in your notes.
You need one for: Elastic PE; Chemical PE; and Gravitational PE

17. Elastic Potential Energy
If you stretch a rubber band and let it go, it sails across the room
As it flies through the air, it has kinetic energy due to its motion but where did this kinetic energy come from?
The stretched rubber band had energy stored as elastic potential energy
Elastic potential energy is energy stored by something that can stretch or compress, such as a rubber band or spring

18. Chemical Potential Energy
Gasoline, food, and other substances have chemical potential energy
Energy stored due to chemical bonds is chemical potential energy
Energy is stored due to the bonds that hold the atoms together and is released when the gas is burned

19. Gravitational Potential Energy
Any system that has objects that are attracted to each other through gravity has gravitational potential energy
Gravitational potential energy (GPE) - energy due to gravitational forces between objects
Water and Earth
Apple and Earth

20. Gravitational Potential Energy
Depends on mass and height
PE = mgh
PE = Ep = m (kg) x g (m/s2) x h (m)
where g is the force caused by gravity (9.8 m/s2)
If you stand on a 3-meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board
A person with 3 times a larger mass has 3 times the potential energy

21. Gravitational Potential Energy
A waterfall, a suspension bridge, and a falling snowflake all have gravitational potential energy

22. Check for Understanding
Ek = 1 mv2 2
What is the kinetic energy of a 100 kg man moving 5 m/s?
What is the kinetic energy of 0.5 kg ball moving at 30 m/s?

23. Check for Understanding
Ek = 1 mv2 2
What is the kinetic energy of a 100 kg man moving 5 m/s?
1 mv2 = 1 x 100kg x (5m/s)2 = 1250 J
What is the kinetic energy of 0.5 kg ball moving at 30 m/s?
1 mv2 = 1 x 0.5kg x (30m/s)2 = 225 J
Eureka! Kinetic Energy

24. Check for Understanding
Ep = m x g x h
A 100 kg boulder is on the edge of the cliff 10 m off the ground. How much energy does it have?
A 0.5 kg ball is thrown 15 m into the air How much potential energy does it have at its highest point?

25. Check for Understanding
E = m x g x h
A 100 kg boulder is on the edge of the cliff 10 m off the ground. How much energy does it have?
100kg x 9.8 m/s2 x 10m = ~ 10,000 J
A 0.5 kg ball is thrown 15 m into the air How much potential energy does it have at its highest point?
0.5 kg x 9.8 m/s2 x 15m = ~ 75 J
Eureka! Potential Energy

26. ANSWER QUESTION 10

27. The Law of Conservation of Energy
The Law of Conservation of Energy- energy can be neither created nor destroyed by ordinary means, it can only be converted from one form to another
Energy can change from one form to another, but the total amount of energy never changes
The total energy of a system remains constant

28. Energy Transformations
The law of conservation of energy is a universal principle that describes what happens to energy as it is transferred from one object to another or as it is transformed
You are likely to think of energy as race cars roar past or as your body uses energy from food to help it move, or as the Sun warms your skin on a summer day
These situations involve energy changing from one form to another form

29. Mechanical Energy Transformations
Mechanical energy is the sum of the kinetic energy and potential energy of the objects in a system
The mechanical energy of a system remains constant or nearly constant
In these cases, energy is only converted between different forms of mechanical energy

30. Mechanical Energy Transformations
An apple-Earth system has gravitational potential energy due to the gravitational force between apple and Earth
The instant the apple comes loose from the tree:
It accelerates due to gravity
It loses height so the gravitational potential energy decreases
Its potential energy is transformed into kinetic as the speed of the apple increases
The potential energy that the apple lost is gained back as kinetic energy so the total amount of energy remains the same

31. Energy Transformation in Projectile Motion
Energy transformations also occur during projectile motion when an object moves in a curved path
However, the mechanical energy of the ball-Earth system remains constant as it rises and falls

32. Energy Transformation in a Basketball
Ball speeds up
Ball slows down
Force of
gravity

33. Energy Transformation in a Roller Coaster
At the point of maximum potential energy, the car has minimum kinetic energy.
Total energy is conserved and constant

34. Energy Transformations in a Swing
When you ride on a swing part of the fun is the feeling of almost falling as you drop from the highest point to the lowest point of the swing’s path
The ride starts with a push that gets you moving, giving you kinetic energy
As the swing rises, you lose speed but gain height
In energy terms, kinetic energy changes to gravitational potential energy

35. The Effect of Friction
You know that if you don’t continue to pump a swing or get a push, your arcs will become lower and you eventually will stop swinging
In other words, the mechanical (kinetic and potential) energy of the swing decreases, as if the energy were being destroyed or lost Is this a violation of the law of conservation of energy?

36. The Effect of Friction NO!!! Energy in the system is conserved
With every movement, the swing’s chains rub on their hooks and air pushes on the rider
Friction and air resistance cause some of the mechanical energy of the swing to change to thermal energy
With every pass of the swing, the temperature of the hooks and the air increases a little, so the mechanical energy of the swing is not destroyed, but transformed into thermal energy, or heat

37. Conservation of Energy with a Pendulum
When is the pendulum moving the fastest?
at the lowest point

38. Conservation of Energy with a Pendulum
When does the pendulum have the most kinetic energy?
at the lowest point

39. Conservation of Energy with a Pendulum
When does the pendulum have the most
gravitational potential energy?
at the highest point

40. Conservation of Energy with a PendulumK E

41. Conservation of Energy with a PendulumK E
Gravitational potential energy depends on height

42. Conservation of Energy with a PendulumK E
Kinetic energy depends on speed

43. E = P + K P K E

44. Total Energy Doesn’t ChangeP + K = E

45. A Pendulum PE PE
All KE
No KE
No KE

46. Transforming Electrical Energy
Light bulbs transform electrical energy into light so you can see
The warmth you feel around the bulb is evidence that some of that electrical energy is transformed into thermal energy, or heat

47. Transforming Chemical Energy
Fuel stores chemical potential energy
An engine transforms chemical potential energy of gasoline molecules into the kinetic energy of a moving car or bus
Several energy conversions occur in this process
In a car, a spark plug fires, initiating the conversion of chemical potential energy into thermal energy
As the hot gases expand, thermal energy is converted into kinetic energy

48. Transforming Chemical Energy
Some chemical energy transformations are less obvious because they do not result in visible motion, sound, heat or light
Every green plant you see converts the radiant energy from the Sun into the energy stored in chemical bonds in the plant, like in carbohydrates (sugars)
When we eat we transform the potential energy stored in the carbohydrate bonds and transform it into kinetic energy

49. Other Energy Conversions
In a battery, chemical energy is converted into electromagnetic energy
The mechanical energy of a waterfall is converted to electrical energy in a generator
Chemical  Thermal Mechanical

50. Check for UnderstandingB
Where is the gravitational potential energy maximum?
Where is the kinetic energy maximum?
Where is the gravitational potential energy minimum?
Where is the kinetic energy minimum?

51. Check for UnderstandingB
Where is the gravitational potential energy maximum? A and E
Where is the kinetic energy maximum? C
Where is the gravitational potential energy minimum? C
Where is the kinetic energy minimum? A and E

52. Exit Ticket
Describe in your own words what the difference between KE and PE is.