Mechanical energy
Mechanical energy is the form this chapter is about, and it comes in exactly two kinds.
Potential energy
Energy a body holds because of where it is, or because its shape has been changed.
Kinetic energy
Energy a body holds because it is moving.
Telling them apart
One question separates them, and it needs no calculation.
- Is the body moving? Then it has kinetic energy.
- Has the body been raised, or stretched, or bent? Then it has potential energy.
A body can hold both at once
These are not alternatives. A ball thrown upwards is moving and is also above the ground, so it holds kinetic and potential energy at the same moment — and as it rises it trades one for the other.