# Gyroscopes and Boomerangs Dr Hugh Hunt

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## Gyroscopes

Gyroscopes are fascinating, counterintuitive and yet their behaviour is completely described by Newton's 2nd Law of Motion "F=ma". This page provides links to various intersting experiments and animations related to gyroscopes.

Virtual Gyroscopes:
Movies, animations, demonstrations and explanations

Spinning tops
Why does a spinning top stay up?
Here are two explanations, one based on the gyroscopic effect and another one that is not. See which one you prefer!

A Gyroscope on gimbals always points in the same direction:
Gyroscope on top of a car
Here the angular momentum of the gyro is conserved both in magnitude and direction because the frictioness gimbals transmit no external couple.

A Gyroscope is apparently an anti-gravity device:
Actually, if you measure the weight of a gyro with a spring balance you discover that the spin makes no difference no weight loss
Then things get fun when you try to pick up a heavy motorzed gyro and hold it above your head gyroscopic acrobatics

Prof Eric Laithwaite Christmas Lecture to the Royal Institution, 1974: Laithwaite Lecture
This link is provided for interest only - I do not share Professor Laithwaite's views on Newtonian mechanics as applied to gyroscopic motion. Gyroscopes are not antigravity devices and cannot be used as "reactionless drives". They do not levitate of their own accord. A spinning rotor does not magically "cancel out" centrifugal force. Gyroscopes are not in themselves useful as a propulsion system for inter-stellar space travel. These are some of the bogus claims made by Laithewaite and his supporters.

• Virtual Gyroscopes
To see Laithwaite's demonstrations with clear explanations go to Emma Wilson's Virtual Gyroscope page

The Wikipedia article opens with the paragraph
"A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. A mechanical gyroscope is essentially a spinning wheel or disk whose axle is free to take any orientation. This orientation changes much less in response to a given external torque than it would without the large angular momentum associated with the gyroscope's high rate of spin. Since external torque is minimized by mounting the device in gimbals, its orientation remains nearly fixed, regardless of any motion of the platform on which it is mounted. Solid state gyroscopes also exist."

This is in fact a description of a "gyrostat" and so is incorrect as a description of a gyroscope. If the orientation of a gyro is fixed then it is incapable of measuring or influencing orientation - yet most applications of gyros are within a control system where the orientation is not fixed. This is especially true of strapdown systems. The idea that "solid state gyroscopes also exist" is incorrect. A "solid state gyro" is not a rotor on gimbals. It is a device for measuring rotation and it usually employs a vibrating beam, or perhaps a laser ring.

• Virtual Gyroscopes
To see Laithwaite's demonstrations with clear explanations go to Emma Wilson's Virtual Gyroscope page

There are plenty of wonderful observations to be made with gyroscopes, and all can be explained with the application of Newton's Laws of motion, in particular F=ma. The catch is that F=ma applies to the motion of a particle and a spinning disc is a rigid body. The motion of rigid bodies needs to be deduced as the integrated sum of the motion of all its component particles. Truly wonderful stuff!

• ## Boomerangs

The boomerang is governed by the gyroscopic effect and aerodynamic lift - two of the most mis-understood areas of physics. This page provides links which I hope will demystify much of the behaviour of boomerangs.

Make your own boomerang: Bang up a boomerang

Making boomerangs is easy: Click here for a one-page handout suitable for printing

Boomerang Theory: Simplified boomerang theory and Detailed mathematics

How to make a cross-shaped indoor boomerang: How to make a boomerang

Boomerang Movies

• National Science Week Schools Roadshow
Here is a link to a fun news bulletin on Boomerangs in Trinity College Cambridge and lectures to Schools for the National Science Week Schools Roadshow. Available either as
WMV, 2.2MB or AVI, 8MB (playing time = 3 minutes)
Other clips are at WMV1 (1.6MB) and at WMV3 (0.3MB).

• Trinity College Science Society Lecture
Boomerangs, bouncing balls and other spinning things. TCSS Lecture (1 hour, WMV format)