APR-06-2015 Work-Kinetic Energy Theorem Activity

Work-Kinetic Energy Lab

(Experiment I: Work done by a non-constant spring force)

Purpose:  To use a force probe and motion sensor to determine the work done by a non-constant spring force.

Procedure:  After properly calibrating the force probe, the apparatus was assembled.  The apparatus includes a cart, track, spring, force probe, and motion sensor (shown below).  

(Complete apparatus - Motion Sensor side)

(Cart /Spring/ Force Probe side)

Using the Logger Pro software, we opened the file L11E202 (Stretching Spring) in order to obtain a force vs. position axes.  After zeroing the force probe, we began collecting data with Logger Pro.  The graph of force vs. position is shown:

(Force vs. Position)

Given the equation:

     F = kx

    k = F / x

    m = y / x = slope

The Spring Constant is the Slope of the F vs. P graph.

k = 2.956 N/m

To find the work done in STRETCHING THE SPRING, we simply integrate to find the area under this graph:

(Integration of Force vs. Position)

The Work done in Stretching the spring is:

    W = 0.1274 N*m

(Experiment II: Kinetic energy and the Work-Kinetic Energy Principle)

Procedure:  For this experiment, we will be releasing the cart from rest while the spring pulls it back.  This allows us to determine the work done BY THE SPRING, as well as the change in KE of the cart.  We first created a new calculated column within Logger Pro in order to calculate the KE of the cart at any point.  

(Graph 1 of Force (purple) vs. Position AND KE vs. Position)

(Graph 2)

What these graphs SHOULD be showing is how the work done by the spring SHOULD be equal to the KE at that point.  What these graphs DO show, is error in our calculated column for KE, and an extreme one at that.