Kinetic energy (KE) is proportional to the square of the speed of the object; KE is therefore a number and not a vector. In order to understand how to use energy correctly, we will also need t...Kinetic energy (KE) is proportional to the square of the speed of the object; KE is therefore a number and not a vector. In order to understand how to use energy correctly, we will also need to discuss isolated systems, potential energy, and internal energy.