The Voyager program produced some of the most remarkable spacecraft ever built, providing an unprecedented view of nearly every planet in the solar system. As Voyager II approached the planet Uranus, the spacecraft precisely trained its instruments on that planet's surface to take advantage of the short window of opportunity to get high-resolution, close-up pictures. Just as the reel-to-reel tape recorder on the spacecraft turned on to capture this historic moment, the orientation of the spacecraft was thrown out of whack and the navigational system had to compensate with last-minute corrections. This project helps you investigate why this could have happened.
What You Need
- freely rotating stool
- bicycle tire with handles (the more massive the better)
- 2 people
- Sit on the rotating stool as before.
- Have someone hand you the bicycle tire that had previously been set into motion. See Figure 59-1.
- Start with the tire in a horizontal position.
- With the tire rotating, turn the tire upside down (so it is now spinning in the opposite direction).
- Wait a few seconds. Then, turn the tire upside down again.
You will rotate on the stool in the opposite direction from which the tire is rotating. While changing the position of the tire, you will feel a surprisingly strong force, as if you were pushing against a solid wall (Figure 59-2).
Why It Works
Starting from rest, both the person and the stool have zero angular momentum. For angular momentum to be conserved, it is necessary that the person on the stool rotate in the opposite direction as the rotation of the tire to preserve angular momentum. When the reel-to-reel tape recorder on Voyager II turned on to record the spectacular images of Uranus for the first time in history, it began turning with a new angular momentum. See Figure 59-3. Just like the person on the stool, Voyager began to turn in the opposite direction as the tape recorder to conserve angular momentum.
Other Things to Try
This principle is demonstrated by a toy train running on a circular track. The track is mounted on a platform attached to a freely rotating support. As the train moves in one direction, the platform rotates in the opposite direction to conserve angular momentum.
Angular momentum is conserved. This applies to the case where a system starts with zero angular momentum.