Plab 223 Lab 1: Motion Detectors and Numerical Models

I am going to try posting the lab as a blog post like this. If it doesn’t work, I will do something else.

Really, there are two objectives in this lab.

Collecting Data

The first thing is to practice and become familiar with the tools you will use to collect data. We will use the Vernier motion detectors quite a bit. I will show you how to use these.

Things to do:

  • Put a cart on a track and move it away from the detector. Which way is a positive x-velocity?
  • Move the cart back and forth. Make a plot of position vs. time. See if you can predict what the velocity vs. time and the acceleration vs. time graph would look like. Use Logger Pro to check yourself.
  • What would you have to do to the cart to make x vs. t graph a straight horizontal line?
  • What would you have to do to make the v vs. t graph a straight horizontal line?

Another motion:

  • Now give the cart a little push and let it roll on the track. Try to make the track level.
  • Determine the x-velocity of the cart after you pushed it.

Fan carts:

  • Turn on the fan and release the cart from rest. Record a graph of x vs. t and v vs. t.
  • In a one-second interval, what is the change in momentum? Could you write this as a vector?
  • In a two second interval, what is the change in momentum? Does it matter which 2 second interval you choose?
  • Can you find the net force during these intervals?

Turn the fan around.

  • Now give the cart a push.
  • Record x vs. t and v vs. t graphs.
  • Compute Δp during several time intervals (including some while the cart comes back towards the detector.
  • For all the Δp that you calculated, how does the net force compare?

Numerical Models

Maybe you should start by watching this very excellent video.

computation introduction 4 from occam98 on Vimeo.

And here is another post about numerical calculations: http://www.wired.com/wiredscience/2008/10/basics-numerical-calculations/

What to do next? I put a pdf file in blackboard with the rest of the instructions.

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