What is it?

A gyroscope is really just a spinning wheel. What makes a spinning wheel interesting is the fact that it resists changes in its orientation along the roll and yaw axis (counting the pitch axis as the spinning motion of the wheel). Because of this, a gyroscope can be used as a stable reference point to measure the change of orientation of something else.

If you were to take a bicycle wheel off of the frame and give it a good spin, holding it by the axle, you would have a pretty good gyroscope going. A bicycle wheel has some decent mass to it, and the fact that most of it is located around the circumference gives it good rotational inertia. It is this rotational inertia that creates the gyroscope effect.

If you were to take the bicycle wheel at rest and rotate it along any axis, it would move around pretty easily. All you are fighting is the inertia of the wheel's mass, which isn't much. But give it a good spin and suddenly you've granted it a large amount of rotational inertia. Rotational inertia is a measure of how difficult it is to change the way something is spinning.

What does it do?

Intuitively, the faster you spin the wheel and the more massive the wheel is, the more difficult it would be to stop the wheel from spinning. Somewhat less intuitively, the greater the percentage of the wheel's mass is located around the circumference, rather than near the axle, the more difficult it would be to stop the wheel from spinning (consider how much easier it is to twirl a large sledgehammer while holding the head rather than the handle).

Where the gyroscope baffles intuition, however, is the fact that its rotational inertia not only makes it difficult to stop the rotation, but also makes it difficult to change what plane it is rotating in. If you hold the spinning bicycle wheel vertically and try to angle it so that it is spinning in the horizontal plane, you will feel the wheel resisting your efforts. Likewise, if you hold it facing North and South, it will resist being moved to rotate facing East and West.

A classroom physics demonstration I once heard about involves two briefcases, one with an iron weight in it and one with a spinning gyroscope. Because of the iron weight, both briefcases weighed the same. There was no apparent difference between them when picked up. However, if two students are instructed to each pick up one briefcase, walk to the end of the desk, and then turn a corner, the results can be almost slapstick in nature. The normal weighted briefcase will offer little resistance to the sudden right-angle change in direction, but the gyroscope briefcase will continue in a straight line, seemingly of its own volition, while the student turns the corner, causing him to lose his balance and stumble.

So how do we explain this behavior?

We can simplify the case by looking at a spinning baton, which is a rod weighted on both ends rather than a continuous circle. The weights move in a circular motion as the baton is spun. As the baton is being spun, we can apply a force to the weighted ends in opposite directions, such that it would twist the baton out of its plane of rotation. Say weight A is pushed left and weight B is pushed right.

180 degrees later, the weights are on opposite sides of the circle from where they were before. Weight A is now in the location experiencing a force to the right. Weight A carries its leftward force to this side, canceling out the rightward force being applied on this side. Likewise, the rightward force of weight B is carried to where the leftward force is being applied, and cancels it out. The baton just canceled out its own imbalanced forces because of its rotation, maintaining the original plane of rotation.

The continuous wheel of the gyroscope behaves in a similar manner, except the forces are continuous along the entire wheel, which gives it even more resistance to change.

Well this is all rather nifty, but what can we use it for?

The gyroscope effect is present whenever a wheel with significant mass is spun. A bicycle will of course benefit from it, since the example we've been using all along was a bicycle wheel. In the bicycle's case, the gyroscope effect of the wheels will help keep the bicycle upright and resist falling over, because falling over would be a change in the rotational plane of the wheels. It also helps the bicycle maintain a course roughly straight ahead, because turning would also be a change in the rotational plane of the wheels, which allows a confident rider to take his hands off the handlebars. We can see, however, that a change in pitch is not resisted if we attain a significant rate of speed and suddenly apply only the front brakes.

The gyroscope effect is likewise present in toys such as the yo-yo and the Frisbee. In the case of a yo-yo, any change in the plane of rotation would prevent the yo-yo from traveling up and down the string smoothly, so the spinning motion of the yo-yo helps it. In the case of the Frisbee, the spinning motion keeps it parallel to the ground so that it flies in a straight line. The more spin you give a Frisbee, the better it will fly. There also exists a wrist strengthening ball which has a gyroscope inside of it, and fighting the gyroscope by rotating the ball by moving your hand around gives the wrist quite a workout.

In more practical applications, the gyroscope is used as a reference point to measure orientation changes in aircraft, submarines, and missiles. This is possible by mounting the gyroscope on gimbals (low friction mounts which can be freely moved around, allowing the gyroscope to remain in its original orientation as the frame changes orientation around it). Several gyroscopes are used in order to measure all the axis of rotation, because a single gyroscope cannot measure pitch, after all that's the direction it's spinning in. Satellites and space stations contain multiple gyroscopes, because in free fall they are the only reference point available. Some of these gyroscopes will be redundant, so a single failure will not be catastrophic for the multi-billion dollar project.

A gyroscope is a disc, weighted heavily and evenly around the outside, that spins quickly around an axis. When spinning fast enough the gyroscope will resist gravity and 'stand up'. The most basic of gyroscopes is the common spinning top.

Gyroscopes have been in use for thousands of years, though originally they were used in the form of spinning tops to entertain and in ceremonies. It wasn't until the mid 1700s that Serson, an English scientist came up with the theory that a gyroscope, since it remains level despite the movement of its surface, could be used as a navigation tool in a ship. This was useful as sextants were the main device used to navigate but they relied on the stars and the horizon. Serson theorized that the gyroscope could be used as an artificial horizon.

In the 19th century Fleuriais designed a gyroscope that made using them much more efficient. Since a gyroscope stops spinning due to friction Fleuriais made a gyroscope with holes on the rim. By blowing air into the holes the gyroscope was kept spinning, and therefore it was kept upright.

A gyroscope acts according to Newton's Second Law, which can be seen at work with the formula f=ma, which shows that force (f) is directly proportional to the size of the mass (m) and acceleration (a). At a certain speed the gyroscope will resist certain forces, such as gravity, and remain upright. This is due to the conservation of angular momentum. Angular momentum is the rotating force of any particle. In a gyroscope, which has no point on around its edge with more or less weight then any other point, this means that every point is spinning at the same speed, and no point is moving faster or slower than any other point.

This also means that gravity is not acting at any greater magnitude on one point than it is on any other point around the edge of the gyroscope, keeping the gyroscope balanced due to constant velocity and gravitational forces across the gyroscope. This keeps the gyroscope upright.

When a force is applied to the axis precession occurs. Precession is the change in the direction of the axis of a rotating object, and occurs due to torque, which is a movement at an angle rather than a push or pull. As precession only occurs due to torque, the movement must be at an angle, such as turning left or right, or the front or back of the axis being forced up or down.

A gyroscope will try to keep itself level to minimize energy used, which, in conjunction with the force of gravity, is why a car will try to level itself out when going up a hill by rolling down. In a boat or plane this can result in the vehicle turning about the center of gravity in the vehicle.

As friction, either air resistance, or the friction on the bearings of the axis of the gyroscope, reduces the speed of the gyroscopes rotation. This means that if the speed of the spin of the gyroscope is not kept constant then the gyroscope's rotation will slow down. Gravity will begin to have a greater hold on the vertical position of the gyroscope, and eventually the gyroscope will slow down enough for gravity to pull it down to the surface it is on. This is because when the forces of angular momentum and gravitational pull are not balanced, the gyroscope will not remain standing.

Torque is a rotational force on the axis or disc. It can be in the form of air resistance, other friction or a push or pull on the direction of the gyroscope. Torque acts like acceleration acting on a moving object; it either compliments the movement and speeds up the rotation or acts against its movement and slows down the spin. If a sufficient enough negative torque is applied it can change the direction of the spin entirely, just like negative acceleration on a moving object.

To reduce the precession of a gyroscope it is often gimbaled so the disc remains suspended in the same plane regardless of other forces. When a gyroscope is gimbaled if has two rings around it that are mounted on an axis at 90� to each other. By adding the two gimbals the gyroscope is supported and so is unable to show precession when a force acts upon the spinning disc's axis.

These days gyroscopes are used in many difference devices for navigation, stabilization or to follow the movement of objects. Boats and planes use gyro-compasses that are basically gyroscopes that are mounted so they can move freely. This acts like a compass as it always points the same way, but as it is not affected by the magnetic north it can be more accurate.

In order to keep robots upright and balanced gyroscopes are used. This concept is also used in computer pointing devices. They gyroscope inside the device tracks the movement of the hand and translates them into cursor movements. Gyroscopes are also used for stability in motorbikes, as otherwise the bike would not remain upright when moving.

This writeup was brought to you by NYH. If you've seen this on your desk, don't panic, I may be your Physics student.

Gy"ro*scope (?), n. [Gr. ring, circle + -scope.]

1.

A rotating wheel, mounted in a ring or rings, for illustrating the dynamics of rotating bodies, the composition of rotations, etc. It was devised by Professor W. R. Johnson, in 1832, by whom it was called the rotascope.

2.

A form of the above apparatus, invented by M. Foucault, mounted so delicately as to render visible the rotation of the earth, through the tendency of the rotating wheel to preserve a constant plane of rotation, independently of the earth's motion.

© Webster 1913.