lab 9 - WORK AND ENERGY Purpose To look at the transfer of...

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34 WORK AND ENERGY Purpose To look at the transfer of energy from one form to another and the work involved when using conservative forces such as that produced by gravity and non-conservative forces like that of friction from the dragging of the aircar on a table. Apparatus Computer, Motion sensor, force sensor with cushion hat, stand, Air-track, glider with rubber band attached, ruler, block of wood, meterstick. Background The work performed on an object is equal to the product of the component, in the direction of movement of the object, of a constant force and the magnitude of the displacement. Mathematically put W = F cos( θ ) s E q . 1 ) where W is the work performed on the object, F cos( θ ) is the component of the constant force F exerted on the object in the same direction that the object has moved, and s represents the magnitude of the object’s displacement. The force does not have to be constant in order for it to do work on an object. The force can vary in magnitude over distance as seen in the force versus distance graph of figure 1. In this situation the total work performed on an object is equal to the area under the force versus displacement curve for the displacement over which the force was exerted. Figure 1 illustrates that the work performed on an object moving from position x o to x f is equal to the area under the force versus displacement curve from positions x o to x f . We will be examining this idea in part 2 of this experiment. Force D istance X o X f Figure 1. This illustrates that the area under the force versus distance curve from x o to x f is equal to the work performed by the force on an object. It is also important to realize that the net work performed on an object is equal to the object’s change in kinetic energy. W net = Δ Ke E q . 2 )
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35 The change in the object’s kinetic energy means that the object’s speed has been affected by the applied force and is written mathematically as Δ Ke = 1 / 2 mv 2 - 1 / 2 mv o 2 Eq. 3) Forces are normally classified into either conservative or non-conservative forces. Conservative forces have the property that the amount of work performed on an object between two points is independent of the path that the object takes, and only dependent upon the initial and final positions. It also has the property that zero work is performed on the object if the object takes a closed path, its initial and final positions being the same. A non-conservative force changes the total energy of the system.
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lab 9 - WORK AND ENERGY Purpose To look at the transfer of...

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