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Phys Lab 4

# Phys Lab 4 - WorkDoneBySprings OnAnAirGlider JohnDomanick...

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Work Done By Springs On An Air Glider John Domanick 10/12/10 Partners: Jordan Pardo, Matt Weiner Teaching Fellow: Tim Harden

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Abstract: In this experiment we investigated the force of two springs on a glider on an air track. Specifically we investigated how measured forces at specific interval of spring stretch compare to those theoretically predicted for the same stretch distances. We also then compared the work done by the springs on the glider to the change in kinetic energy of the glider, to verify the work‐energy theorem. We know that springs exert position dependent forces on the body on which they act, and there should be no difference in these forces, whether measured static, as an equilibrium measurement, or dynamically, by measuring acceleration of the body due to the force. We also know that the work a force does is equal to the change in kinetic energy of the object the force acts on, and again there should be no difference in the work if we measure statically as an integral of a function of forces, or dynamically as the kinetic energy of the object. We found that in each part of our experiment the static and dynamic measurements of both force and work are not in agreement. The forces we measured only agreed 4 out of 11 trials, and only just. The work we measured, statically was 0.040J, and kinetically was 0.046018+/‐1.68145x10 ‐9 J.
Theory: The force that a spring exerts on a body is a position dependent force, that is to say, that the force varies with the distance that the spring is either stretched or compressed. An ideal spring follows Hooke’s Law, and the force is equal to: F s = kx (1) where k is the spring constant, essentially the stiffness of the spring, and x is the stretch/compression distance from its equilibrium point. To predict the force of the spring at various points of stretch, we attached multiple known masses to the springs, over a pulley. Here we knew that once the spring reached its new equilibrium point, that the spring’s force would be equal to the tension in the string connecting the weight and springs, and that the tension was equal to the force of gravity on the weight. F g = mg = F T = F s (2) To measure the experimental force of the springs on the glider, we had to measure the acceleration of the glider as it passed through each of the equilibrium points, previously determined with known masses. Using a photogate system we were able to measure the acceleration of the glider along its motion. We could then calculate the force of the springs on the glider by: F net = ma = F s (3) where a is the acceleration of the glider at the equilibrium point, and m is the mass of the glider.

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