PURPOSE: To develop 3-dimensional visualization skills.

DESCRIPTION: Plastic frame with two colored rods. The trick here is to determine, solely by looking at the frame from two sides set 90o apart (as seen below) whether the sticks are touching or not. Click here to see a short movie of the frame rotating, which will reveal the answer.

If they were touching, the relative position of the point of contact between them would be the same from all viewpoints. It is not, therefore the rods are not touching.

SUGGESTIONS: See Question of the Week #289 for information on using this demonstration to enhance class involvement.


EQUIPMENT: Plastic frame containing two colored rods.

SETUP TIME: 10 min.

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