Making One Link Control Another





Overview

Students try to build a pegboard mechanism in which one strip controls another. In order to do so, they will invent a new way to use a fastener.  They observe the directions that each strip moves.


Materials

  • Pegboard bases, strips and fasteners (as in Lesson 1)
  • Science notebooks
  • Work Sheet: Which Way will it Move?

Procedure

1.       Introduction to Materials and Activity:

Demonstrate a strip connected to a based by two fasteners and a strip connected to a base by one fastener. Review the difference between a structure and a mechanism, and how to convert one to the other.

Present the challenge: Make a mechanism using two strips so that one strip controls the other.  One strip controls another when it makes the other strip move back and forth.

2.      Student Activity

As students work, pose productive questions to further their inquiries.  Here is a video on productive questions and samples of good questions to ask.

Science Notebook

  • Make a diagram of your mechanism. 
  • Describe how it works.
  • After the class discussion, label the input and output of your mechanism.

3.      Whole-class discussion:

Gather students' constructions and analyze them as to whether they are structures or mechanisms. For those that are mechanisms, analyze them as to whether one piece controls another. See this video.

Introduce the terms “input” and “output”.   Then students operate and describe their constructions using “input”, “output” and “control.”  As students become fluent with. “input”, “output” and “control,” introduce the terms “fixed pivot” and “floating pivot.” They should include these terms in their descriptions of their mechanisms. Here are suggestions for the discussion.

Focus students’ attention on the direction of motion of input and output, and on the relative locations of the fixed pivot and the floating pivot. This is crucial to understanding how mechanisms move. Here are suggestions for the discussion, and drawings.

4.      Homework: Complete the Lesson 3 Worksheet: Which Way will it Move? 

5.      Extension:  Circle the 1st class levers on the Lesson 3 Worksheet.

Outcomes

1.      Students make a mechanism where one strip (the input) controls the movement of a second strip (the lever).  The output of the mechanism is located on the lever. For most of our work we consider the output to be at the end of the lever. 

2.      Students discover that in order to make one strip control another, they will need to use a fastener that connects one strip to another, but not to the base.

3.      Students become familiar with the terms “input”, “output”, “fixed pivot” and “floating pivot”

4.      Students recognize that

  • the input and the output go in the same direction when the input (and floating pivot) are between the fixed pivot and the output and that
  • the input and the output go in the opposite direction when the fixed pivot is between the input and the output

Troubleshooting

The issues students encounter have to do with the way their mechanisms work - or don't work -  and how to represent them. Here are videos to address these issues.

Issues with the way the mechanisms work.
Nothing moves.
One link sometimes turns the other.
One link hits the other back and forth.
One link pushes but does not pull the other.
The end of the lever (the output) moves in the wrong direction.
The end of the lever does not move enough.
Nothing is controlled

Issues with how to draw the mechanism.
What should be included?
Identifying pivots.
Drawing in  proportion



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