# 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 [(mass_{1})(velocity_{1}) +(mass_{2})(velocity_{2})] .
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)(M_{1})(
2v_{1}) = M_{1}v_{1}.

**Procedure: **

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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Last Modified 02/14/03