1. Energy Storage
Potential Energy

2. What is energy?
Energy measures the ability for things to change themselves or to cause change in other things.
Some examples are changes in temperature, speed, position, pressure, or any other physical variable.
Pushing a 1-kilogram object with a force of one newton for a distance of one meter uses one joule of energy.

3. Mechanical Energy
Mechanical energy is the energy possessed by an object due to its motion or its position.
Potential energy and kinetic energy are both forms of mechanical energy.

4. Chemical Energy
Chemical energy is a form of energy stored in molecules.
Batteries are storage devices for chemical energy.

5. Electrical Energy
Electrical energy comes from electric charge, which is one of the fundamental properties of all matter.

6. Nuclear Energy/Radiant Energy
Nuclear energy is a form of energy stored in the nuclei of atoms.
In the Sun, nuclear energy is transformed to heat that eventually escapes the sun as radiant energy.
Radiant energy is energy that is carried by electromagnetic waves.
Light is one form of radiant energy.

7. The electromagnetic spectrum includes visible light infrared radiation (heat), and ultraviolet light.
Light energy and heat energy are included in the electromagnetic spectrum.

9. Kinetic/Potential Energy of motion is called kinetic energy.
A moving car has kinetic energy because it can hit another object and cause change.
Systems or objects with potential energy are able to exert forces (exchange energy) as they change.
Potential energy is energy due to position.

10. Gravitational Potential Energy
Objects high above the ground have energy by virtue of their height.  This is potential energy (the gravitational type).  If allowed to fall, the energy of such an object can be converted into other forms like kinetic energy, heat, and sound.  Gravitational potential energy is given by:
The equation shows that . . .
the more mass a body has
or the stronger the gravitational field it’s in
or the higher up it is
. . . the more gravitational potential energy it’s got.

11. SI Potential Energy Units
From the equation  U = m g h  the units of gravitational potential energy must be:
kg · (m/s2) · m  = (kg · m/s2) · m  =  N · m    =  J
This shows the SI unit for potential energy is the Joule, as it is for work and all other types of energy.

12. Reference point for PE is arbitrary
Gravitational potential energy depends on an object’s height, but how is the height measured?  It could be measured from the floor, from ground level, from sea level, etc.  It doesn’t matter what we choose as a reference point (the place where the potential energy is zero) so long as we are consistent.  
Example:  A 190 kg mountain goat is perched precariously atop a 220 m mountain ledge.  How much gravitational potential energy does it have?
PEgravity = mgh = (190) (9.8) (220) = J
This is how much energy the goat has with respect to the ground below.  It would be different if we had chosen a different reference point.

13. Elastic Potential Energy
Things that can be stretched or compressed can store energy--elastic potential energy.  Examples: a stretched rubber band; a compressed spring; a bent tree branch on a trebuchet catapult.
The elastic potential energy stored in a spring depends on the amount on stretch or compression and the spring constant.  Recall, Hooke’s law:  F = - k x, where:  F  is the force the spring exerts on whatever is stretching or compressing it;  x  is the amount of stretch or compression from the equilibrium point; and  k  is the spring constant.  Like the force, the potential energy of a spring (or anything that obeys Hooke’s law) depends on  k  and  x.  It is given by:

14. Chemical Potential Energy
Chemicals react with metals, causing excess electrons to build up on the negative electrode and producing a shortage of electrons on the positive electrode.
The difference in the number of electrons between the positive and negative terminals creates the force known as voltage. 
When you connect a battery to a circuit, you provide that alternate path for the electrons to follow.