1. Conservation of Energy
Section 3
Conservation of Energy

2. Essential Questions What is the law of conservation of energy?
What is mechanical energy?
Why is mechanical energy not always conserved?
How are power and energy related?

3. Review Vocabulary
friction: a force that opposes the sliding motion of two surfaces that are touching each other

4. New Vocabulary
law of conservation of energy
mechanical energy
power

5. The Law of Conservation of Energy
The law of conservation of energy states that energy cannot be created or destroyed. Energy can only be converted from one form to another or transferred from one place to another. (Total energy remains constant)
For the roller-coaster cars, energy is converted back and forth between energy and gravitational potential energy.
Some kinetic energy is converted to other forms of energy.
The total amount of energy is constant.
Shenval/Alamy Images

6. Energy Transformations
Examples: Which types of energy do they have?
The sun warming your skin.
An apple falling off of a tree
Eating a granola bar.
Driving a car.
Riding a bike.
Types of energy include: mechanical, electrical, chemical, thermal, and radiant.
Mechanical Energy Transformations
often describe the energy transformations in bicycles, roller coasters, swings, falling objects, and projectiles.
ME is the sum of the KE and PE of the objects in a system.
Includes KE, EPE, and GPE of objects but not nuclear, thermal, or chemical PE

7. The mechanical energy of the bat-ball-Earth system remains constant as the ball rises and falls.

8. Energy Transformations
A ride on a swing illustrates how kinetic energy changes to potential energy
and back to kinetic energy.
The Columbus Dispatch

9. Other Energy Transformations:
Energy transformations can be affected by other forms of energy or forces.
Ex. If you don’t keep getting pushed on a swing or pump, the swing eventually stops. Why???
Air resistance is a force slowing down the velocity of the swing
Friction is a force going against the swing on the metal swing itself.
To keep swinging, you need more mechanical energy (pumping).
Electrical energy is energy used to run electrical devices. Like TV’s, toasters, wash machines, and your stove.
Chemical energy is the energy stored in fuels, plants, or the food we eat. Energy from food is measured in Calories. 10 calories is about 40,000 Joules
Power is the rate at which energy is converted. It is measured in Watts which is 1 Joule per second. Electrical tools and appliances have power ratings.
P = Work energy/ Time