Newton's Laws II

# Newton's Laws II - Applications of Newton's Laws Purpose To...

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Applications of Newton's Laws Purpose: To apply Newton's Laws by applying forces to objects and observing their motion; directly measuring these forces that are applied. Apparatus: Pasco track, Pasco cart, LabPro interface and cables, friction block, force sensor (2), cart-force sensor adapter, motion sensor, pulley, mass bucket & long thin string, thicker short string, assorted mass hanger weights Introduction: In last week's lab, we confirmed Newton's Third Law by having two force sensors interact with each other and verified Newton's Second law in a static situation. This week, you will apply these laws to some dynamic situations, as well as static ones. The power of the Second Law is its ability to predict the motion of objects based on their properties and the forces they are subjected to. We hope that in this lab you will gain hands-on experience with those generic blocks, masses, pulleys, rough and frictionless surfaces that you have been subjected to so many times in lecture, in recitation and in your textbook. Here is one such example - the problem of a mass on surface, attached by a string to another mass hanging over a pulley: If gravity is present and the surface is frictionless, the system (M + m) will no doubt accelerate, with the pulley turning in the counter-clockwise direction (M goes left, m goes down). What is the acceleration of the system? What is the tension in the string before it starts to move and after it starts to move? How would the presence of friction change these values? A critical part of your problem-solving process is setting up a free-body diagram: isolate each mass and identify the forces acting on it.

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We then add up the forces in X and Y directions, and equate them to ma . Since the larger mass does not accelerate in the Y direction, Newton's second law for M reads: F y = 0 = N-Mg (1) There is, however, acceleration in the X direction: F x = Ma (2) where we have given positive signs to forces that tend to make the pulley turn in the direction we expect, i.e. counterclockwise For the smaller mass, there are no forces in the X direction, only the Y direction: F y = ma = mg - T (3) Note that the acceleration for the large mass is the same as that of the small mass, so they
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Newton's Laws II - Applications of Newton's Laws Purpose To...

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