PURPOSE: To encourage students to think about rotational forces and addition of forces.

DESCRIPTION: Attached inside the tube to the center of the rotator are a string, a mass, a second string, a second mass, a third string, and a third mass. Q: As the speed of the rotator is increased, which string will break, the inner string, the middle string, or the outer string? A: The inner string.

SUGGESTIONS: Let your students vote on it before doing the experiment. Some will forget that the forces add, and suggest that the outer string will break.

REFERENCES: (PIRA unavailable.)

EQUIPMENT: Variable speed rotator, tube with masses and strings, counterweight.

SETUP TIME: 5 min.

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