Children begin Lesson 3 by sharing mechanisms they have made. They develop the ideas of input and output by discussing everyday things. Then they figure out how to use another piece to move their mechanism back and forth. To do so, they will have to invent the floating pivot, which attaches two pieces (links) to each other but not to the base.
Inputs and Outputs:
In a whole-class meeting, students show mechanisms they have made and what they need to do to make them move. They describe what each one does to make his or her mechanism move. Then students think of other things they push or pull to make them work. Examples might include lights, pencil sharpeners, doors, or retractable ball point pens.
Levers and Handles:
Demonstrate the Butterfly-net MechAnimation. Ask students:
Students show how they have met the challenge of making a handle (the input) for their mechanisms. They are likely to think of simply pushing the lever with the input, rather than with their fingers directly. Congratulate them on that solution, but then use their mechanism to demonstrate what happens when you try to pull the lever back with the input. Because they are not connected, the input will not be able to pull it back.
The Floating Pivot:
At least one student will probably come up with the idea of attaching the input to the lever with a fastener that goes through the two moving parts but not through the base. We will call this type of pivot a floating pivot. If students have not invented the floating pivot yet, make such a mechanism yourself.
Lead a discussion based on what children have made.
Using words and pictures, explain how you made a mechanism with an input, which controls it.
Students should be able to:
Demonstrate a simple lever, attached to a base with a fixed pivot and ask;