What Happens to the Spring Scale Readings in a Moving Elevator?

Personal Lab 4

Background

We have seen that the motions of freely falling objects are so fast that the human eye has difficulty discerning details about the speeds during a fall. From the height of two meters, an object in free-fall reaches the ground in a mere 0.6 seconds.

The astronauts in the Space Shuttle are in a "low Earth" orbit, meaning that they orbit the Earth only a few hundred kilometers above the ground where the force of gravity is about 93% that on the ground. If the force of the Earth’s gravity is nearly the same as on the ground, then why do the astronauts experience "weightlessness" while orbiting the Earth?

With the aid of your Spring Scale and fishing weights, you will study a remarkably fundamental aspect of motion while riding an elevator.

Purpose

1. To investigate the factors that influence the readings on the Spring Scale in a moving elevator.

2. To understand why astronauts aboard the Space Shuttle appear to be "weightless".

Materials

Procedure

1. Make predictions about how both upward and downward motions of the elevator will affect the force readings (in Newtons) for a fishing weight suspended from your Spring Scale. Enter the predictions in your Lab Book.

2. Take your fishing weights and Spring Scale to a convenient elevator.

3. Perform various experiments to investigate the effects (if any) of an elevator’s motion on the Spring Scale readings. You may need to ride the elevator up and down several times.

Questions

1. Describe what happened to the Spring Scale readings as the elevator moved upward.

2. Describe what happened to the readings during the downward motion of the elevator.

3. What do you conclude about the influence of the elevator’s motion on the Spring Scale readings? Explain your reasoning.

4. What would be the Spring Scale reading if you were to repeat this experiment during the free-fall part of a sky-diving jump from an airplane? Explain your reasoning.

5. What would be the Spring Scale reading if you were to take the fishing weight and your Spring Scale along while orbiting the Earth aboard the Space Shuttle? Explain your reasoning. (Remember that the Space Shuttle is in a low-Earth orbit, where the effects of the Earth’s gravity are nearly as strong as on the ground.)

6. What would you expect would happen if you were to weigh yourself during the upward part of an elevator ride? the downward part? (You may test your predictions by performing these experiments during one of the Tuesday or Wednesday labs in H357, where there is a portable scale available.)

7. What would you weigh aboard the Space Shuttle while in low-Earth orbit? Explain your reasoning.

8. What would be your "weight" during the free-fall part of a sky dive jump from an airplane? Explain your reasoning.

9. In your own words explain what the term "weightlessness" means.

10. Explain the terms "weight", "acceleration" and "force".

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Last modified 9 Aug 1997
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