We saw in the last lecture that work is the transfer of energy from one object (the object exerting the force) to another object (the object feeling the force):  W = F_x x.  If W > 0, then energy is transferred to the object experiencing the force, while if W < 0, the energy is being taken from that object.

In what follows we will recall the definition of power, and then consider further the concept of work along with the potential energy defined in the last lecture. This will lead us to the extremely important idea of the conservation  of energy, which is the main point of this lecture.