1. Section 2
Describing Energy

2. Essential Questions
What is the difference between kinetic energy and potential energy?
How can you calculate kinetic energy?
What are some different forms of potential energy?
How can you calculate gravitational potential energy?

3. Review Vocabulary
work: a force applied through a distance

4. New Vocabulary energy elastic potential energy system
chemical potential energy
kinetic energy
gravitational potential energy
potential energy

5. Change Requires Energy
When something is able to change its surroundings or itself, it has energy.
Energy is the ability to cause change. Without energy, nothing would ever change.
Example: The moving tennis racket in the figure below has energy. That racket causes change when it deforms the tennis ball and changes the tennis ball’s motion.
Ted Kinsman/Science Source

6. What is a system?
The tennis and the racket are systems. A system is anything around which you can imagine a boundary.
It can be a single object
It can be a group of objects
One system can do work on a second system and transfer the energy to it.

7. Different Forms of Energy
Energy has many different forms: they include mechanical energy, electrical energy, chemical energy, and radiant energy.
Kinetic Energy – energy due to motion. Examples – a car moving on a highway, frog leaping in the grass.
KE = ½ mv²
KE is measured in joules.
Potential Energy – energy that is stored due to the interactions between objects. Ex. Energy stored in a ball before it rolls down a hill.
Elastic Potential Energy – the energy of a compressed spring or rubber band that is stored inside of it.
(l)Comstock Images/Alamy, (tr)Pixel Shepherd/Pixtal/age fotostock, (br)Brand X Pictures/PunchStock

8. Different Forms of Energy
Chemical Potential Energy - energy that is due to chemical bonds. Examples are the energy stored in the foods we eat.
Gravitational Potential Energy (GPE)– energy that is due to the gravitational forces between objects. Example the apple and the Earth have GPE because gravity pulls down on the apple.
GPE = mgh where m = mass, g = 9.8 n/Kg, h = height
The higher an object is off of the ground, the more GPE it has in it.

9. Assessment 1.
The gravitational potential energy of a cucumber-Earth system changes when which factor changes?
the cucumber’s speed A
the cucumber’s mass B
CORRECT
the cucumber’s temperature C
the cucumber’s length D

10. Assessment 2.
Which energy transformation is happening in the figure at the right?
kinetic energy to GPE A
The Columbus Dispatch
GPE to kinetic energy B
CORRECT
thermal energy to mechanical energy C
mechanical energy to chemical potential energy D

11. Assessment 3.
Friction causes mechanical energy to be converted into which form?
thermal energy A
CORRECT
nuclear energy B
kinetic energy C
potential energy D