Force and Motion Laboratory

A) Changing force

  1. Place the pulley on the end of the track without the stop, and hang the end over the table.  Make sure the track is level.  Place the motion detector at the other end, and the cart with force sensor and cart masses in the middle, with the hook toward the pulley.  Take the plastic cup with the string, and hook a loop of the string on the hook of the force sensor.  The string should be of the length that the cup is high--almost to the pulley--when the cart is a little further than 30 cm (1 foot) from the motion detector.  It should look something like this
    Picture of cart on track with sensors and pulley
  2. Load the DataStudio file ForceAndMotion.ds if not already loaded. Clear any data from DataStudio by using "Clear Last Data Run" or "Clear All Data Runs" under the "Experiment" menu.
  3. Unhook the string from the force sensor, press the zero button, and put the string back on.  Hold  the cart a little more than 30 cm from the motion sensor, start DataStudio, and let the cart roll toward the pulley.  In order to get good, clean data, you need to keep the force of the force sensor cord from affecting the cart.  Do this by picking up the cord loosely ~ 40 cm from the sensor, hold it slack, and then move your hand with the cart so that the cord stays slack the entire time.
  4. Measure the average force and average acceleration of the cart during the time it is moving freely.  Do this by click-dragging a rectangle around the data points with the mouse highlighting the yellow, and then looking at the mean value in the key.  Record the and acceleration and force in a chart in your notes, or switch to the "Acc. vs. Force" data table in DataStudio. 
  5. Without erasing your data (unless your are going to re-do a run), repeat steps 3&4 with different masses in the cup: 10 g, 20 g, 30g, 40g, 50g, and a run in which the string is not hooked onto the sensor.
  6. If you haven't already done it, enter your acceleration and force data in the "Acc. vs. Force" data table.   Look at the "Acc. vs. Force" graph, fit it, and draw the graph on a white board and add the equation.
  7. Save your DataStudio file for future reference. 
  8. Measure the mass of the cart just like it was pulled--same masses on it, holding the cord like you held it when it was pulled.
  9. For the lab report, you will need the graph of acceleration, velocity and force for the 6 runs, your chart of acceleration and force data, and the graph with fit.  You could save those in a Word document for future reference.
  10. Enter the fit parameters and the cart mass into the Google data form to share with the class.

B) Changing Mass

  1. Use the same set up from the first part, except with 20g in the cup, and no extra masses on the cart.  Clear all data if there is some
  2. Take data as in the first part, remembering to zero the force sensor without the screen before each run.
  3. Repeat, adding additional mass to the cart, in 200 to 250 gram increments, until there is at least 1.0 kg on the cart.
  4. Place the data in the "Acc. vs. Mass" data table.  Look at the "Acc. vs. Mass" graph, and choose an appropriate fit.
  5. Draw your graph and equation  on a white board.
  6. Find the typical force on the cart while it was being pulled from your Acceleration, Velocity, Force graph. 
  7. Enter the fit parameters and typical force in a Google form for sharing with the class.
  8. Save your acceleration vs. mass data and graph, fit parameters and typical force for use in your writeup.