Question

What is the difference between kinetic and potential energy and how do they work?

Answer 1

To explain, I will use the equations for kinetic and potential energy:

$PE = mgh\\KE = \frac{1}{2}mv^{2}$

Potential energy

Potential energy is the potential an object has to move due to gravity.  An object can only have potential energy if 1) gravity is present and 2) it is above the ground at height h.  If gravity = 0 or height = 0, there is no potential energy.  Example:

An object of 5 kg is sitting on a table 5 meters above the ground on earth (g = 9.8 m/s^2).  What is the object's gravitational potential energy?  (answer: 5*5*9.8 = 245 J)

(gravitational potential energy is potential energy)

Kinetic energy

Kinetic energy is the energy of an object has while in motion.  An object can only have kinetic energy if the object has a non-zero velocity (it is moving and not stationary).  An example:

An object of 5 kg is moving at 5 m/s.  What is the object's kinetic energy?  (answer: 5*5 = 25 J)

Kinetic and Potential Energy

Sometimes, an object can have both kinetic and potential energy.  If an object is moving (kinetic energy) and is above the ground (potential), it will have both.  To find the total (mechanical) energy, you can add the kinetic and potential energies together.  An example:

An object of 5 kg is moving on a 5 meter table at 10 m/s.  What is the objects mechanical (total) energy?  (answer: KE = .5(5)(10^2) = 250 J; PE = (5)(9.8)(5) = 245 J; total: 245 + 250 = 495 J)