Naked Science Forum
General Science => General Science => Topic started by: Seany on 13/05/2007 23:16:49
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These thing are fascinating things!! They spin even though the bottom of it doesn't spin!! What is it..?! It's fascinating! Also, they spin for agessssss!
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.graphcomprints.com%2FImages-new%2Fgyroscope.gif&hash=266198e2324035419c8cb4cdf515ee90)
I've got one myself.. They are amazing! I've lost the piece of string though.. It doesn't work now!!
They have also made this! It is also with this gyroscope business!!
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fabc.net.au%2Fnews%2Findepth%2Fyir2001%2Fphotos%2Fsegway.jpg&hash=65543c7e3db3566a80ed70185d8ed00d)
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There are a number of different effects involved in a gyroscope.
Firstly, the aspect of spin and inertia.
It is in essence the same thing as when you spin yourself around with arms outstretched, and weights attached to your arms. You can feel the weights pulling your arms out, but because the two arms are balanced, so they don't actually pull your body either one way or the other.
When you spin with your arms outstretched, because their is air between your arms, so there will be aerodynamic drag on your arms to slow you down, but with a solid disk, there is no air to get between the spinning parts, so the only aerodynamic drag is the slight friction with the air on the surface of the disk. The greater friction is on the bearings where the spinning parts meet the stationary parts of the gyroscope (if you want to remove both of these, then you can spin the gyroscope in a vacuum, and suspend it on magnets).
The more complex issue is to explain how a gyroscope derives its stability.
I suppose the easiest place to start is to think about newtons first law of motion that will mean an object will continue moving in a straight line until something defects it. Now wrap that in a circle, and you have a gyroscope.
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A Giroscope is what unemployed people use to look for the postman when their benefit is due [:D]
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Firstly, the aspect of spin and inertia.
Can we call it angular momentum, please?
I don't want to appear grumpy but I have a bit of crusade against 'inertia' which is not really a defined quantity. If one person means one thing and someone else means another then then cofusion reigns.
Having said that, rotational mechanics is too hard for me guv.
Eric Laithwait, of linear electric motor and maglev fame and a giant amongst engineers had a lot of trouble with the establishment simply because he found the rotational vector sums too hard and needed some help to explain the fact that his sums seemed to predict a 'reactionless force' under some circumstances. He asked for help but no one would get involved - labelled, very unfairly, as a crank, by many. This has still not been resolved completely, I believe.
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Can we call it angular momentum, please?
I don't want to appear grumpy but I have a bit of crusade against 'inertia' which is not really a defined quantity. If one person means one thing and someone else means another then then cofusion reigns.
I would much rather that 'cofusion' reigned than that 'confusion' might reign [;D]
More seriously, the point was that I did not want to talk about quantities but about qualities, and so tried deliberately not to include terms that had clear quantitative meaning.
If we were calculating angular momentum, then I would agree the calculation would require it to be angular momentum and not angular inertia. Hopefully, as a quality, it did not cause confusion (I cannot say whether it might have caused cofusion [:)]).
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You got me there!
But does your 'inertia' refer to something moving, not moving or trying not to move?
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But does your 'inertia' refer to something moving, not moving or trying not to move?
Strictly speaking, the root of the word 'inertia' is 'inert'.
I would say that it is best thought of as being impervious to environmental influence, although ofcourse this can be very contextual (one might be impervious in one context, but not another; and thus have inertia in one context and not another).
Since we are talking about motion, or lack of it; thus in that context we are talking about how impervious the item is to forces that might cause a change in its motion.
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Ahh... Me is confused... So how does the thing spin around, without the actual tip of the bottom spinning?
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Ahh... Me is confused... So how does the thing spin around, without the actual tip of the bottom spinning?
It spins on bearings.
Bearings can be all sorts of things, but they have a common aim to support (bear the weight of) a rotating component within a stationary engine.
The simplest bearings on gyroscopes (of the type you pictured above) have very smell cones fitted into a hole of a similar (but slightly wider) shape.
The idea is that the cone within a conical hole will be locked into place (i.e. cannot slip out of place, so the axle and disk is locked into the machine), but because the only are of contact is the very small point at the tip of the cone, so there is a very small actual area of friction when the axle rotates, so you can limit the amount of energy lost through friction.
There are lots of other ways of doing the same thing if you want an ultra isolated gyroscope (as you typically would use for navigation systems), but the bearings used here are more than adequate for the design of a toy gyroscope.
Incidentally, if you were to somehow suspend the entire gyroscope mechanism (not just the inner part) so that it was not connected to the outside world (e.g. suspend it in a gravity free environment), you will find that as friction does effect the inner and out parts of the gyroscope, so the outer part will start to spin up as the inner part slows down. It is only because the outer frame is usually resting on a surface that prevents it from spinning, and the bearings are good enough to provide some reasonable (but imperfect) isolation between the inner and outer parts, that the outer parts remain stationary while the inner part will continue to rotate for some time before losing its energy.
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There is a story (could be true) about a gyro in the inertial(!!!) guidance system of a rocket that was built in the UK. The gyro was spun up and tested, then the rocket was shipped to Australia for testing.
The gyro kept spinning on its excellent bearings, stayed pointing the same way on its journey and ended up 'upside down' on arrival in Oz.
No one spotted the inversion when they turned on the control circuits.
On being launched, the rocket aimed for the ground!
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There is a story (could be true) about a gyro in the inertial(!!!) guidance system of a rocket that was built in the UK. The gyro was spun up and tested, then the rocket was shipped to Australia for testing.
The gyro kept spinning on its excellent bearings, stayed pointing the same way on its journey and ended up 'upside down' on arrival in Oz.
No one spotted the inversion when they turned on the control circuits.
On being launched, the rocket aimed for the ground!
Fantastic! It seems a comic's story!