Force and motion


8. How much do outputs move?


Students experiment with an input link and two output links to see how the positions of the fixed pivots change the amount the output moves. They discover that when the fixed and floating pivots are close together, the output moves a lot. When they are further apart, the output does not move as much .


  • Pegboard base, three pegboard strips (two with numbers) and four pivots per student.
  • Two 2” x 2” squares of paper for each student to tape to the two outputs.


  1. Setting-up the experiment:
    Distribute the pegboard materials: pivots, paper squares and tape, and show students how to assemble the H mechanism. (See video and instructions)

  2. Carrying out an experiment:
    Students connect the bottom links of the H mechanism to the base, one through the 4” hole, the other through the 0” hole (See a video). They tape a paper square to the top of each output link. Observe the movement of each output as you move the input link back and forth. Record your observations in your science notebook. Here are some suggestions for entries.

  3. Quick Share:
    Ask two students to demonstrate their mechanisms and tell their stories. Have them point out the fixed and floating pivots, and which output moves more. Here is a video on important share points.

  4. More experiments:
    Tell students to remove the fixed pivots and do two more experiments. For each experiment put the fixed pivots in different positions on the output links. Here are suggestions for science notebook entries.

  5. Class discussion about how inputs and outputs move:
    Students bring their last mechanisms to the class meeting. They are to be used to illustrate points students make about how the input and outputs move. Here is a video on outcomes of the discussion.


Directions the outputs move

  • When the fixed pivot is between the floating pivot and the output, the input and output go in opposite directions.
  • When the floating pivot is between the fixed pivot and the output, the input and the output move in the same direction.


Amounts the outputs move

  • When the fixed pivot and floating pivot are moved closer together, the output moves more.
  • When the fixed pivot and the floating pivot are moved further apart, the output moves a shorter distance.