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Force and motion

MechAnimations

5. Directions of Motion

Overview

Students compare the directions of motion between the input and output, and learn to make mechanisms of two types using pegboard.

Materials

  • Pegboard bases (one per student), strips (two per student) and fasteners
  • Tape and yellow and red squares to attach to pegboard.
  • Science Notebooks

Procedure

  1. Demonstrate a “same” and an “opposite” mechanism: Demonstrate a mechanism where input and output go in the same direction. Place a yellow post-it on the input and output. Then demonstrate a mechanism where the input and output go in opposite directions. Place a red post-it on the input and output. (See a video on “same” and “opposite” mechanisms.) Ask students to identify the input of each mechanism.

    • Look very carefully as I operate the input of this mechanism (a “same” mechanism). Which way does the output go when I move the input to the right? Which way does it go when I move the input to the left?
    • Now watch as I operate the input of this mechanism (an “opposite” mechanism). Which way does the output go when I move the input to the right? Which way does it go when I move the input to the left?
    • What is different in the way these mechanisms move? (See the video on comparing “same” and “opposite” mechanisms.)

  2. Make an “opposite” mechanism: Provide each student with a pegboard base, two links and fasteners. The design challenge is this: Make a mechanism where the output moves in the opposite direction as the input. When the mechanisms are made, provide red post-its to place on the input and output. Ask students to compare the way their mechanisms move with the mechanisms of others in their group. Draw your “opposite” mechanism in your science notebook.

  3. Make a “same” mechanism: Students remove the post-its, then convert their mechanisms so the input and output move in the same directions. When the mechanisms are completed, they place yellow post-its on the input and output. Students compare the way their mechanisms move with the mechanisms of others in their group. Then they draw their “same” mechanisms in their science notebooks.

  4. Whole-class discussion: Ask a student to make a drawing of a “same” mechanism on chart paper, and another to make a drawing of an “opposite” mechanism. Remind them to distinguish between fixed pivots and floating pivots. See a video on comparing “Same” and “Opposite” mechanisms.

    • Does anyone disagree that this is a way to make a “same” mechanism, and that this is a way to make an “opposite” mechanism?
    • Does anyone have a different way to make a “same” or an “opposite” mechanism?
    • How can you convert a “same” mechanism to an “opposite” mechanism?
    • What is a way to be sure that the mechanism will be a “same” mechanism?
    • What is a way to make sure that the mechanism will be an “opposite” mechanism? Ask students to record these conclusions in their science notebooks.

Outcome

Students should discover that:

  1. To make the input and output move in opposite directions you have to put the fixed pivot between the floating pivot and the output.
  2. To make the input and output move in the same direction you have to put the fixed pivot on the opposite side from both the floating pivot and the output.