Conservation of energy: a gyroscope resists movement - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: December 02, 2018, 03:16:23 pm
content: If you spin up a gyro scope then your start slowly spinning it in a direction it resists where does the energy go? I know 99.9999% of "lost" energy goes into heat. For example "AvE" on youtube has a video where he puts a big glob of grease on one of two really good bearings that spin for minutes on their own. Then he takes the greasy one and spins it by hand since it won't spin on its own and the FLiR shows a visable differance in temperature of the two, I knew that but thought it would be 0.00001'C, but grease that reduces friction can cause a lot of friction, ironically. This gave me the idea of what if you tried this with gyro scopes and saw if their bearings got hot. Is this where the energy from your hands turning it in a resistive axis goes; it puts stress on the bearings? Or do the gyro scopes actually slow down from angular momentum being transfered from movement? This is the only example I can think of to get rid of motion energy and not generate heat or make a magnetic field. You could "absorb" energy without making heat. I wonder if there are any engineering types on this board...

author: apis
author_rank: Super Contributor
timestamp: December 02, 2018, 06:17:44 pm
content: Hmm, maybe some can give a proper answer with equations and all, but I would guess it's not because of friction. You transfer energy somehow to the rotating mass. A gyroscope should work the same even if the bearings were perfect (i.e. no frictional losses). That said, since the bearings are not perfect, there will be losses there and those should increase when you rotate the gyro since that would increase the forces acting on the bearings.

author: Andy Watson
author_rank: Super Contributor
timestamp: December 02, 2018, 06:33:21 pm
content: Quote from: Beamin on December 02, 2018, 03:16:23 pmI agree with Apis - you transfer energy to the wheel - so it speeds up. I believe that is that basis of these excercise//toy balls:https://en.wikipedia.org/wiki/Gyroscopic_exercise_tool

author: EmmanuelFaure
author_rank: Regular Contributor
timestamp: December 02, 2018, 07:30:00 pm
content: The primary goal of a grease is to reduce wear, not friction.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 02, 2018, 11:46:32 pm
content: Gyroscopes and other instruments have a carefully optimized amount of lubrication, usually an oil. Too little or two much increases friction losses. The optimum amount is far smaller than a glob, typically a small fraction of a drop. These rotating masses will then spin for minutes or longer. The friction losses are so small that heating of the bearings is somewhere close to or actually is undetectable.As others have said, the work done in moving the spin axis of the gyro goes into the angular momentum of the rotor, either increasing spin or reducing it depending on how the work is done.

author: Brumby
author_rank: Unknown
timestamp: December 03, 2018, 01:43:47 am
content: Gyroscopes do not lose energy by the fact of their rotation. Consider spacecraft that are given a spin for gyroscopic stability. One spin and they keep going.Gyroscopes lose energy from:* friction in their bearings* air friction from their rotating surfaces* in the case of an electrically conductive rotor in a magnetic field, the subsequent eddy currents will result in heating of the rotor and corresponding loss of angular momentumIn all cases, heat is the final disposition of the energy lost.When you spin a gyroscope up by hand, you are applying one force tangentially to the rim of the flywheel, but as you are holding the frame of the gyroscope, there is an opposing force applied at the bearings. This opposing force stops the gyroscope from being launched into the air, but because the two forces are acting at two different points of the flywheel, there is a turning moment on it. With the flywheel on bearings, this turning moment causes the it to rotate. These exact same forces are in play when you use a string to accelerate the flywheel - just that the radius of the applied force is smaller (decreasing the mechanical advantage, but increasing the maximum speed achievable) and the length of time it is applied is longer.

author: Circlotron
author_rank: Super Contributor
timestamp: December 03, 2018, 02:27:42 am
content: Quote from: Andy Watson on December 02, 2018, 06:33:21 pmBeat me to it!I have often thought that you could use this principle as the basis for extracting energy from waves. The random up and down movement could be used to tilt the gyro, therefore adding energy to its rotating mass.A cool experiment would be to lay a big gyro horizontally with its axis in an east-west direction. As the earth rotates the gyro is gradually tilted end over end, and if it is constrained from trying to skew "sideways" then energy from the rotating earth will be added to the gyro's rotating mass. The faster it is initially spinning, the more will be added from moment to moment because it is harder to "tilt".

author: Brumby
author_rank: Unknown
timestamp: December 03, 2018, 02:53:02 am
content: Quote from: Andy Watson on December 02, 2018, 06:33:21 pmNever thought about gyroscopes that closely.I learned something today!

author: Beamin
author_rank: Super Contributor
timestamp: December 04, 2018, 08:53:52 am
content: Quote from: CatalinaWOW on December 02, 2018, 11:46:32 pmI will try to find the AVE video because I thought the same thing. Just a few turns of the greased up bearings and you can see the change in color on the flir. Was quite amazing grease has so much friction for a whats just basically a fluid being stretched and moved around.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 04, 2018, 10:45:26 am
content: I am sure that you can see temperature change in a heavily greased bearing. Numbers always matter. Friction in a bearing system can change by orders of magnitude with different lube conditions. For a simple experiment take a bearing you have, put 90 weight single viscosity oil on it and get familiar with how easily it turns. Better yesterday, measure running torque at some known rpm. Then put it in the freezer until the temperature stabilizes and repeat.