Author: admin
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Newton’s Second Law for a System of Particles
Now that we know how to locate the center of mass of a system of particles, we discuss how external forces can move a center of mass. Let us start with a simple system of two billiard balls. If you roll a cue ball at a second billiard ball that is at rest, you expect…
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The Center of Mass
We define the center of mass (com) of a system of particles (such as a person) in order to predict the possible motion of the system. The center of mass of a system of particles is the point that moves as though (1) all of the system’s mass were concentrated there and (2) all external forces were…
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What Is Physics?
Every mechanical engineer hired as an expert witness to reconstruct a traffic accident uses physics. Every trainer who coaches a ballerina on how to leap uses physics. Indeed, analyzing complicated motion of any sort requires simplification via an understanding of physics. In this chapter we discuss how the complicated motion of a system of objects,…
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Conservation of Energy
We now have discussed several situations in which energy is transferred to or from objects and systems, much like money is transferred between accounts. In each situation we assume that the energy that was involved could always be accounted for; that is, energy could not magically appear or disappear. In more formal language, we assumed…
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Reading a Potential Energy Curve
Once again we consider a particle that is part of a system in which a conservative force acts. This time suppose that the particle is constrained to move along an x axis while the conservative force does work on it. We can learn a lot about the motion of the particle from a plot of the system’s…
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Conservation of Mechanical Energy
The mechanical energy Emec of a system is the sum of its potential energy U and the kinetic energy K of the objects within it: In this section, we examine what happens to this mechanical energy when only conservative forces cause energy transfers within the system — that is, when frictional and drag forces do not act on the objects in the…
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Determining Potential Energy Values
Here we find equations that give the value of the two types of potential energy discussed in this chapter: gravitational potential energy and elastic potential energy. However, first we must find a general relation between a conservative force and the associated potential energy. Consider a particle-like object that is part of a system in which…
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Path Independence of Conservative Forces
The primary test for determining whether a force is conservative or nonconservative is this: Let the force act on a particle that moves along any closed path, beginning at some initial position and eventually returning to that position (so that the particle makes a round trip beginning and ending at the initial position). The force is conservative only if…
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Work and Potential Energy
we discussed the relation between work and a change in kinetic energy. Here we discuss the relation between work and a change in potential energy. Let us throw a tomato upward (Fig. 8-2). We already know that as the tomato rises, the work Wg done on the tomato by the gravitational force is negative because the force…
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What Is Physics?
One job of physics is to identify the different types of energy in the world, especially those that are of common importance. One general type of energy is potential energy U. Technically, potential energy is energy that can be associated with the configuration (arrangement) of a system of objects that exert forces on one another. This is…