![]() In this case, F cos θ F cos θ is constant. In equation form, this is W net = F net d cos θ W net = F net d cos θ where θ θ is the angle between the force vector and the displacement vector.įigure 7.3(a) shows a graph of force versus displacement for the component of the force in the direction of the displacement-that is, an F cos θ F cos θ vs. The net work can be written in terms of the net force on an object. Net work is defined to be the sum of work on an object. Let us start by considering the total, or net, work done on a system. ![]() We will see in this section that work done by the net force gives a system energy of motion, and in the process we will also find an expression for the energy of motion. We know from the study of Newton’s laws in Dynamics: Force and Newton's Laws of Motion that net force causes acceleration. We will also develop definitions of important forms of energy, such as the energy of motion. We will find that some types of work leave the energy of a system constant, for example, whereas others change the system in some way, such as making it move. In this section we begin the study of various types of work and forms of energy. Some of the energy imparted to the stone blocks in lifting them during construction of the pyramids remains in the stone-Earth system and has the potential to do work. In fact, the building of the pyramids in ancient Egypt is an example of storing energy in a system by doing work on the system. In contrast, work done on the briefcase by the person carrying it up stairs in Figure 7.2(d) is stored in the briefcase-Earth system and can be recovered at any time, as shown in Figure 7.2(e). ![]() For example, if the lawn mower in Figure 7.2(a) is pushed just hard enough to keep it going at a constant speed, then energy put into the mower by the person is removed continuously by friction, and eventually leaves the system in the form of heat transfer. What happens to the work done on a system? Energy is transferred into the system, but in what form? Does it remain in the system or move on? The answers depend on the situation. Explain and apply the work-energy theorem.Explain work as a transfer of energy and net work as the work done by the net force.By the end of this section, you will be able to:
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