Motivated by a MechAnimation, a Whale Chasing a Boat, students experiment with a mechanism having two outputs, the H mechanism. They experiment by moving the fixed pivots and see the difference the position of the fixed pivot makes in how the output moves.
- Windshield Wipers mechanism.
- Mechanimation: A Whale Chasing a Boat.
- Pegboard base, three pegboard strips and four fasteners per student.
- Two Post-its for each student to tape to the two outputs.
1. In a class meeting, demonstrate a pegboard windshield wiper mechanism. Invite students to brainstorm what it could be. Then demonstrate the Whale Chasing a Boat. Ask students to predict what the mechanism looks like that makes the MechAnimation move the way it does. Compare it to the windshield wiper. Students will discover how to make a mechanism move in different ways by experimenting with the H mechanism
2. The H mechanism experiment. Distribute the materials and show students how to assemble the H mechanism. Students connect the outputs (levers) of the H mechanism to the base, one through the 4” hole, the other through the 0” hole. This video shows how to use the H mechanism. Students tape a paper square to the top of each output link. They record how the outputs move in the science notebook.
- Make a drawing of the mechanism you made.
- Show the fixed pivots and floating pivots and use arrows to show how the input and outputs move.
- Write “more” next to the output that moves more.
- How does this compare to the Whale Chasing the Boat?
3. Quick Share. Ask two students to demonstrate their mechanisms and tell a story it might animate. Have them point out the fixed and floating pivots, and which output moves more.
4. More H experiments. Students remove the fixed pivots and do two more experiments. First they put a fixed pivot through the 2” hole of one lever and a fixed pivot through the 7” hole of the other lever. For the second experiment they put the fixed pivots anywhere they wish. Record the results in the science notebook.
5. Class discussion: How do the outputs move? Students use their last mechanism to illustrate how the input and outputs move. Here are outcomes of the discussion an questions that will lead to them.
a. What did you discover about the movement of the input and the output?
b. What did you discover about how much the output moved?
6. Complete the Lesson 6 Worksheet: How the Outputs Move and insert it in the science notebook.
1. 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.
2. 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.