How do gyroscopes help maintain orientation?

1. This toy has a heavy wheel on a thin axle. Balance it on the tower and let go. It tips over at once, just like a pencil standing on its point.
2. Now wind a string around the axle and pull. The wheel spins very fast. Put it back on the tower and it balances, even when it leans. The spin is holding it up.
3. Here is the strange part. Gravity still tries to tip the wheel over. But a spinning wheel answers a push by moving sideways. So instead of falling, it circles slowly around the tower.
4. Now mount the spinning wheel inside a ring so it can turn freely. Tilt the stand and the ring tilts with it, but the wheel keeps pointing the same way. The rings are called gimbals.
5. Rubbing in the bearings and the air slowly steal the spin. As the wheel slows, the stand can drag it along more and more easily. A gyroscope only works while it spins fast.
6. On a ship rocking in the waves, a spinning gyroscope still points the same way. Ships, airplanes and spacecraft use gyroscopes to know which way they are tilting and turning.

Tap each part. Watch what spins, what tilts and what stays still.

• Rotor. The rotor is a heavy wheel with most of its weight at the rim. Heavy and fast means it is very hard to tilt.
• Axle and pointer. The rotor spins around the axle. The direction of the axle is what the gyroscope keeps steady, so we put a pointer on it.
• Cage. The cage holds both ends of the axle and does not spin. It lets you hold the gyroscope without touching the whirling rotor.
• Bearings. At each end of the axle, a smooth bearing lets it turn with very little rubbing. Less rubbing means the wheel spins for longer.
• Gimbal ring. The cage sits on a pivot inside this ring. When the stand tilts, the ring turns around the wheel instead of dragging the wheel with it.
• Stand. The stand is fixed to whatever carries the gyroscope: a boat, a plane or your hand. It tilts and turns with them.
• Pull string. The string is wound around the axle. Pulling it hard unwinds it and sets the rotor spinning.

Tilt the boat with the wheel still, then with it spinning fast. When does the arrow stay on the star, and when does it get dragged along?

Experiment: You tilt the boat. What does the arrow do when the wheel is spinning fast?

1. Leave the wheel still and tilt the boat. Watch the arrow.
2. Set the boat level and aim the arrow at the star again. Then turn the spin up high.
3. Tilt the boat the same way as before. What is different?

What we found: A still wheel is carried along by the boat, because the rubbing in the pivot drags it. A fast-spinning wheel resists being turned so strongly that the same rubbing can hardly move it. The arrow stays on the star while the boat tilts underneath.

Turn on JavaScript to try it yourself.

Choose a rotor, pull the string up to 6 times, then set sail. The arrow must stay near the star for the whole stormy trip.

Anything that moves in a straight line tends to keep going that way. Something similar is true for spinning. A spinning wheel tends to keep spinning, and to keep its axle pointing in the same direction. The heavier the wheel and the faster it spins, the stronger this is.

That is why a spinning top stands up and a rolling coin does not fall over. Try to tip a fast-spinning wheel and it pushes back in a surprising way: it swings sideways instead of going where you push. Scientists call this sideways motion precession. It is why a leaning top circles slowly instead of falling.

A gyroscope uses this effect on purpose. A heavy rotor spins inside rings called gimbals. The rings can turn freely around it, so when a ship or a plane tilts, the rings move but the rotor stays pointing the same way. By comparing the rotor with the ship, the crew can tell exactly how far the ship has tilted or turned.

A gyroscope is not magic. Rubbing in the pivots drags on it a little, so it slowly drifts. And when the spin runs down, it stops working. Our spinning-top comparison is not perfect either: a top stands on the floor, but a gyroscope in gimbals can keep its direction even when its stand is turned upside down.

Key words

Gyroscope

A fast-spinning wheel mounted so that it can keep pointing in one direction.

Rotor

The heavy spinning wheel of a gyroscope.

Gimbal

A ring on pivots that lets what is inside it turn freely.

Angular momentum

How much spinning a thing has. Heavy, wide and fast means a lot.

Precession

The slow circling of a spinning wheel's axle when something tries to tip it.

Check your thinking

1. What keeps a toy gyroscope balanced on its tower?

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   Its fast spin. The spin makes the wheel resist tipping. When the spin runs out, it falls like anything else.

2. A boat tilts to the left. What does a fast-spinning gyroscope on board do?

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   It keeps pointing the way it did before. The gimbal ring turns around the rotor, so the boat's tilt does not reach it.

3. Which rotor will hold its direction best?

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   A heavy one spinning fast. Heavy and fast together give the most spin to hold the direction.

4. Why does a gyroscope stop working after a while if nothing keeps it spinning?

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   Rubbing and air slow the wheel, and a slow wheel is easy to tilt. A gyroscope only resists tilting while it spins fast. Friction takes the spin away.

5. What are the rings around a gyroscope for?

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   They let the stand tilt without tilting the wheel. The rings turn on pivots, so the stand can move around the wheel without dragging it.