University of South Carolina

Physics 101 Spring 2003

Fourth Experiment:  Velocity and Linear Momentum

We will follow procedures similar to the linear momentum lab, (Experiment 7 in the lab book).

Reference:  How Things Work Section 2.3.

Objective:  To observe and understand the conservation of linear motion.

Apparatus:  Air Track, carts, weights, Pasco motion sensors, Pasco Xplorer data gatherers.

Introduction:   Momentum consists of the product of mass times velocity, where velocity is a vector and has a direction as well as a magnitude. In a collision, momentum is always conserved. Conservation means that the amount we start with is the same as the amount we end with. We can see this easily in the collisions of two objects where the total momentum is just [(mass1)(velocity1) +(mass2)(velocity2)] . In all the cases below we compare the initial momentum to the final momentum. The momentum comparisons are estimates. For example, you might observe the following: Cart 2 is moving at twice the velocity after the collision as Cart 1 was initially. Since it has half the mass it has about the same momentum as Cart 1 did initially (1/2)(M1)( 2v1) = M1v1.


The procedure will be given to you in the laboratory. You will first measure velocity with the motion sensor and computer. Then you will study collisions between air-track carts of equal masses and unequal masses. The interpretation of the events can be understood by applying the law of conservation of (linear) momentum.

Please read the discussion and procedure for Exp. 7 in your lab manual. Although we will be using the motion detectors instead of the photogates mentioned in the lab book, the concepts are similar. You will be able to directly find the velocity from the position graphs and the momenta from products of mass with velocity.

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