Mechanism Diagrams

Overview

Students think about how to record their pegboard mechanisms, develop drawing skills, and represent their work in their notebooks through drawings.


Materials

  • Classroom set of pegboard Mech-a-Blocks
  • Simple mechanisms with separate inputs from Lesson 3
  • Chart paper and markers
  • Drawing paper and pencils

Procedure

1.      Why make diagrams? In a whole-class meeting, introduce the recording problem: Pegboard is recyclable, and we can use it again for something else. You can’t take it home, because it costs too much. Suppose you made something, and then planned to take it apart, so you could use the pieces for something new.

  • How could you make a record of what you made, so you could make it again, or compare it with the new mechanism?
  • Suppose you want to tell your parents or a friend about a mechanism you made?

Conduct a discussion about these issues. Students will probably suggest making drawings.

2.      Thinking about diagrams. A diagram looks like a drawing, but its purpose is different. A drawing is supposed to look as much as possible like the real thing. A diagram represents the important features, but not everything – just what you need in order to make it again. Provide some diagrams of your own as examples. Some of them could deliberately be hard to read. Engage students in thinking about what makes a diagram easy or hard to figure out:

  • How much of your mechanism do you need to show, in order for someone to know what you did, or for you to remember later?
  • For example, do you really need to draw in every hole, or just the ones where you put fasteners?

3.      Making diagrams. Provide newsprint and markers, or paper and pencils, and encourage students to record their constructions in any way they choose.

4.      Gallery walk. Once students have created their own diagrams, post them around the room, and conduct a discussion about what you can learn from each one. Find positive features of each one, and use the discussion to develop ideas about what makes a good diagram. You might also compare some of the drawings with the original mechanisms, to look for similarities and differences. The key question is:

  • Would another student be able to make the same mechanism you made if all the information they had was in the diagram?
  • If not, what would you need to do to make the diagram easier to use?

To explore this issue, you could deliberately make a mechanism incorrectly from a student’s diagram that is missing some information, such as the distinction between fixed and floating pivots.

5.      Using symbols in diagrams. Develop a list of symbols already in use in your classroom or school, such as red and green for which doorways to use, bathroom symbols, fire extinguisher symbols, etc.  Connect these symbols in everyday use to the symbols they used in their diagrams:

  • How did we use symbols to show common things, so we don’t have to make a complete drawing each time?
  • What other things would you like to have symbols for?

Help them think about which kinds of things are really different, and therefore need to have different symbols. For example,

  • How could we use symbols to tell whether something is a fixed pivot or a floating pivot?

6.      Science Notebook

At the end of the period, ask each student to remove his or her diagram from the wall and attach it to the Science Notebook.

7.      Outcomes

Students should be able to represent a mechanism using a diagram, and understand how an effective diagram could be used to reconstruct the real thing

8.      Assessment

Show students a Mech-a-Blocks mechanism, accompanied by a diagram that uses the same symbol for fixed and floating pivots. Ask them:

  • If I tried to use this diagram to make this mechanism, what would happen?
  • What other information would I need?

Troubleshooting

Using a drawing where fixed and floating pivots are not distinguished, one might decide to use all fixed pivots.  In this case, nothing would move. So it is important to distinguish between fixed and floating pivots. How might one do this?
  1. Label each pivot in the drawing as "fixed" or "floating."
  2. Use symbols: a solid circle is a fixed pivot, an open circle is a floating pivot.

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