1E10.10 Crossing the River


Relative motion


A toy tractor moves across a piece of paper being pulled along the floor.



  • [1] Tractor toy
  • [1] Large piece of paper
  • [2] Metre stick
  • [2] Lab stand
  • [2] 90-degree clamp
  • [1] Aluminum rod
  • [1] Video camera
  • [1] Tripod

Classroom Assembly

  1. Place the paper flat on the floor.
  2. Slip metre sticks into pockets on the sides of the paper.
  3. Clamp the rod to the lab stands to make a diagonal over the paper.
  4. Mount the camera on the tripod to have an overhead view of the demo.
  5. Plug the camera into power and the video input for the projector.
  6. Check that the camera works.

Important Notes

  • The tractor's battery compartment needs to be securely taped shut for it to work.


  1. Turn on the tractor.
  2. Using the metre sticks as handles, move the paper so that the tractor travels along the rod.
  3. Turn off the tractor.


Additional Resources


  • PIRA 1E10.10


  • Don't attempt this at home!

Last revised

  • 2020


Related AV

Related demos


If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.