1. Conservation of Energy

2. Changing Forms of Energy
Energy is most noticeable as it transforms from one type to another.
What are some examples of transforming electrical energy?
A lightbulb (electric to light)
A hair dryer (electric to heat)

3. Forms of Energy (Review)
Electrical
Radiant (solar rays)
Chemical (petrol)
Nuclear
Sound (vibrations in the air)
Heat

4. Kinetic Energy

5. Kinetic Energy Energy an object has because it is moving.
E.g. a moving car, a running person, a falling basketball.
Kinetic Energy can be calculated using the formula
KE = 0.5 x mv2

6. Kinetic Energy
A child (40kg) running at 5m/s has 500J of kinetic energy
An adult (80kg) running at the same speed has 1000J of kinetic energy
Doubling the mass gives double the kinetic energy
KE = 0.5 x (40 x 52)
KE = 0.5 x (80 x 52)

7. Kinetic Energy An 80kg adult running at 5m/sec has 1000J of energy
The same adult running at 10m/sec (double the speed) has 4000J of energy
If you double the speed the kinetic energy increased four times
KE = 0.5 x (80 x 52)
KE = 0.5 x (80 x 102)

8. Kinetic Energy
An objects speed has a greater influence on kinetic energy than mass
When an object has stopped completely its kinetic energy is 0 even though it still has a mass

9. Potential Energy

10. Potential Energy
Definition: Energy an object has because of its position
1. Examples
a. Gravitational potential energy – potential for an object to move (fall) due to gravity
E.g. a rock on the edge of a cliff
b. Elastic Potential Energy - the potential in a stretched elastic band to snap back into position.
c. Chemical Potential Energy – Energy stored in chemicals. Like petrol and batteries.

11. GPE = mass x gravity x height
Potential Energy
2. The amount of potential energy tends to depend on two factors
A. Mass
B. Tendency to move in a particular direction
Twig Video: Potential Energy
GPE = mass x gravity x height 

12. Elastic Potential Energy
E.g. bungee jumper
When a person stands at the edge of the bridge he has a lot of Potential Energy
When he jumps he has Kinetic Energy
When the rope is fully stretched it has the potential to return the person upwards due to Elastic Potential Energy.

13. Changing forms of Energy
An example of transforming chemical energy is a car engine.
Chemical potential energy in gasoline is transformed into kinetic energy of the car as it moves.

14. KE and PE
In many situations, there is a conversion between potential and kinetic energy.
The total amount of potential and kinetic energy in a system is called the mechanical energy
Mechanical energy = PE + KE

15. Mechanical Energy 1. Mechanical energy is due to the position
and motion of the object.
2. What happens to the mechanical energy of an apple as it falls from a tree?
a. As the apple falls to the ground, its height decreases (position).
b. Therefore, its gravitational potential energy decreases.
c. But, because it is falling (motion), its kinetic energy has increased.
d. To conclude: The potential energy is not lost … it is converted into kinetic energy as the speed of the apple increases.

16. 3. What happens to the mechanical energy (total amount of energy)?
a. The mechanical energy does not change because the loss in potential energy is simply changed into kinetic energy.
The energy in the system remains constant!!
Example showing how total mechanical energy remains the same.
Image 1
Calculation 1
Image 2
Calculation 2
150 PE KE
 ____________ Total: ME
75 PE KE
 _____________
Total: 150 ME

17. Swinging Along
Think about the changes in energy when you are on a swing…
At what point does the person on the swing have the most potential energy? __________________________________________________
At what point does the person on the swing have the most kinetic energy? __________________________________________________
What happens to the mechanical energy when at the top and the bottom of the swing? __________________________________________________

18. The Law of Conservation of Energy
Twig Video: Law of Thermodynamics
1. The Law of Conservation of Energy states that energy cannot be created or destroyed.
2. The big picture… the total energy in the universe remains constant.

19. 3. But how. If I stop pumping while I’m swinging, I stop
3. But how? If I stop pumping while I’m swinging, I stop!! So, where’s the energy?
4. FRICTION - As you swing, the hooks and the chain rub against each other.
5. Friction causes some of the mechanical energy of the swing to change to HEAT energy and the temperature of the hooks and chain heat up a little.
6. AIR RESISTANCE - Causes objects
to slow down due to the friction of
air on them. This resistance transforms
into heat.

20. Quick Quiz What is the ‘conservation of energy’ definition?
What energies combine to create mechanical energy?
The higher an object is in relation to the ground increases what?
If an apple has a potential energy of 85 and a kinetic energy of what is it’s mechanical energy?
What two types of energy transfers occur when swinging that causes you to slow.
Quick Quiz

21. Answers
Energy is neither created or destroyed. It simply changes forms.
Kinetic Energy + Potential Energy
Increases it’s potential energy
Mechanical Energy = 100
Friction of chain on ring and body with the air.

22. Conservation of Energy
Energy is transformed… not destroyed!!
The total amount of energy stays the SAME!!

23. Energy in Your Body
Even the energy converted in your body follows the law of conservation of energy.
Chemical potential energy is transferred to kinetic energy that allows your body to move!!

24. The End