211_Newtons2ndLaw

211_Newtons2ndLaw - Algebra Based Physics Mechanics Lab 3...

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Algebra Based Physics – Mechanics Lab 3 Newton’s Second Law INTRODUCTION According to Newton’s Second law an object will accelerate in the direction of the net force . If F is the net force, and if m is the mass of the object, then the acceleration is given by / a F m = , more familiar to us as F ma = . The purpose of this laboratory exercise is to verify Newton’s Second Law. EXPERIMENTAL SET-UP You will use a special flat track with a very low friction cart. See Figure 1. We know that a cart at rest experiences some forces, such as its weight and the upward force of the tabletop, but if we were to add up all these forces as vectors the net result would be zero—all forces are in balance. It is this NET force that appears in the Second Law, and which, when non-zero, will cause a cart to accelerate. We will supply a non-zero net force by hanging a mass off the end of the track and attaching it to the cart with a long, very light string. Gravity will accelerate the hanging mass ( m 1 ) downward which will provide, through the string, a net force on the cart, ac- celerating it toward the end of the track. A small frictional force is in the opposite direction to the direction of travel, this acceleration causes the object to slow its forward motion. Figure 1 Experimental set-up (schematic) Basic Principles Let’s look at the forces on the masses one at a time. The falling mass is pulled downward by gravity ( 1 g F m g = ) and upward by the tension ( T ) in the string. Thus the Second Law, applied to the falling mass in the y-direction reads, m 2 f m 1 g T T m 1
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Algebra Based Physics – Mechanics Lab 3 (1) Here, the downward direction has been chosen to be positive, since that is the desired direction of motion. Now we have to look at the net force on the second mass. Since the supporting force of the track exactly counteracts the weight of the cart (the cart is not flying upward or falling downward), the net force acting on the cart is the tension in the string. Thus the Second Law, applied to the rolling cart, reads (2) Since we have chosen the downward motion of to be positive, we cannot randomly chose any direction to be positive for . Since are connected by a string, if moves in the positive direction (downward) then
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This note was uploaded on 08/30/2009 for the course CH CH 221 taught by Professor Gorman during the Spring '08 term at N.C. State.

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211_Newtons2ndLaw - Algebra Based Physics Mechanics Lab 3...

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