Energy

First, what is Energy *not*? The idea of energy is confusing to a lot of people. But you need to understand that energy is not a type of substance. It is related to the motion or movement of atoms, molecules, and objects.

What energy *is*: Energy is an abstract (mathematical) measure related to the amount of motion of objects (including atoms and molecules). Energy can be classified into two general categories: kinetic energy and potential energy. Energy related to motion is called "kinetic energy." Energy is also an abstract (mathematical) measure of the potential for more motion. Energy related to the potential for motion is called "potential energy."

Kinetic energy: the abstract (mathematical) way to measure an object's kinetic energy due to movement over a distance is:

• KE (of object) = 1/2*(mass of object)*(speed of object)²

So, you can see from this equation that kinetic energy is a measure of the object's motion: speed (as well as its mass).

Potential energy: An abstract (mathematical) way to measure an object's potential energy (PE) due to gravity is:

• PE (of object) = (mass of object)*(height of object above the ground)*(acceleration due to gravity or "g")

So, both measures of energy include the mass of the object that is either moving or has potential to move. It's not obvious for potential energy, but both measures also include the speed of the object. For the potential energy of an object falling in a vacuum,

• (height of object above the ground)*(acceleration due to gravity) = 1/2*(speed of object right before it hits the ground)²

So, for an object falling in a vacuum:

• PE (of object) = 1/2*(mass of object)*(speed of object right before it hits the ground)²

How do we know that height*acceleration = 1/2(speed)^2?