A2L Item 182

• Description: Identify the correct statements regarding an astronaut in space.
• Goal: Distinguish between mass, gravitational force and weight.
• Source: CT151.2S02-21
• Keywords: Gravity, Mechanics

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The question for students:

An astronaut floats inside an orbiting spacestation. Which of the following are true?

1. No forces act on the astronaut.
2. The astronaut has no mass.
3. The astronaut has no weight.

1. A only
2. B only
3. C only
4. A and B
5. A and C
6. B and C
7. all are true
8. none are true

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Commentary for teachers:

Answer

The only possible answers are #3 and #8. The issue turns on the definition of weight. At the surface of the earth weight and the gravitational force are often considered equivalent. Further, since the gravitational force depends upon the mass, mass and weight are proportional and mass units are sometimes used as a measure of weight. In orbit bodies still experience a gravitational force but are said to have no weight. Is it any wonder that students are confused? Invoking scale readings as weight is not a solution either as one’s weight would change in an elevator. The best solution to this is to sensitize students to these issues and charge them with the responsibilty of determining how to interpret these quantities in context.

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