gyro's left on for 24 hours while the earth spins to find absolute motion? - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: June 23, 2019, 11:22:06 pm
content: If you turned on one of those gyroscopes from the B(52?) Bomber that dave featured in his videos and let it sit on a table wouldn't the gyroscope not stand still but actually slowly spin as the earth spins? Could you use this to find absolute motion somehow of the solar system or even the milky way and then to the extent of the whole universe? Would be cool if he could make some 400hz 110VAC and get it running. Motion be relative to the observer be damned!

author: ataradov
author_rank: Super Contributor
timestamp: June 24, 2019, 12:03:11 am
content: You would have to observe for hundreds of years to detect any sort of movement coming from the galaxy. In realistic times, at most you will see movement of the Earth around the Sun. And even that will take multiple years to get really good data.

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 24, 2019, 02:13:05 am
content: Quote from: ataradov on June 24, 2019, 12:03:11 amI've wondered about what the OP is saying... the earth is spinning, so shouldn't a gyro affixed to the ground detect that we spun around once in 24 hrs (relative to the sun but also relative to the universe, give or take...)?

author: ataradov
author_rank: Super Contributor
timestamp: June 24, 2019, 03:12:17 am
content: Quote from: windsmurf on June 24, 2019, 02:13:05 amIt will, but I doubt there would be enough mechanical precision to detect anything beyond rotation around the Sun. We are not moving around the Milky Way all that fast.

author: Brumby
author_rank: Unknown
timestamp: June 24, 2019, 03:46:09 am
content: Theoretically, yes - but as has been said above, the timeframes and mechanical accracy required make anything outside our solar system completely impractical.

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 24, 2019, 04:12:23 am
content: Quote from: Brumby on June 24, 2019, 03:46:09 amBut a gyroscope is not detecting rotation in relation to the sun right? Its not referencing gravity, is it?Maybe I need to research gyroscope...Any astrophysicists in the house?

author: ataradov
author_rank: Super Contributor
timestamp: June 24, 2019, 04:20:20 am
content: No, it is detecting the rotation relative to a fixed axis that was defined at the time gyroscope was spun on. So in theory it would detect the rotation of the solar system. If the Sun was fixed and did not move, then after a year, the readings would return to the old values. But the Sun and the solar system are also rotating around the galaxy, which is also rotating. So your readings after a year will not return to the old value. The deviation in angles would be that rotation.

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 24, 2019, 04:26:51 am
content: Quote from: ataradov on June 24, 2019, 04:20:20 amSo if I spun a gyroscope and had one of the fixed axis pointing to the north star, shouldn't it always point toward the north star even as the earth rotates?

author: ataradov
author_rank: Super Contributor
timestamp: June 24, 2019, 04:37:20 am
content: If you point it precisely at the north star (and discounting the radius of the planet), then you would not see the effect of rotating around Earth's own axis, but you would still see the rotation around the Sun. It will be minuscule, and probably not even detectable, but it will be there.And if you live in the ideal math universe, then based on the measured angle, and knowing the radius of the Earth's orbit around the Sun, you could calculate the distance to the north star. Obviously this is not possible in practice.

author: rs20
author_rank: Super Contributor
timestamp: June 24, 2019, 04:54:51 am
content: In what sense is the Sun "spinning" around the centre of the galaxy? It'sorbitingthe centre of the galaxy, yes, but spinning is completely open to definition of what you attach your gyroscope to. If you attach your gyroscope to the surface of the Earth, yes, it'll detect the spin of the earth. But what are we attaching the gyroscope to in order to detect the "spin" of the Sun or the solar system?Atarodov, if your point is that a gyroscope on the earth would stay still with respect to distant stars as opposed to the apparent position of the Sun throughout the year, then yes that's true of course, but that's very specifically looking at the apparent direction of the Sun w.r.t. to a gyroscope, rather than just looking at a gyroscope.

author: Beamin
author_rank: Super Contributor
timestamp: June 24, 2019, 11:02:06 am
content: Say you did have a gyro that could measure plank distances in XYZ couldn't you spin it and find an absolute direction violating the whole "always relative to the observer" effect? Whats the most accurate they have now? Back in the 1950's they could get with in a few feet on a NY to LA flight with wind with the exact gyro dave has. How would it look if you attached a gyro to a cosmic microwave background, cmb, photon? Would it move?

author: Brumby
author_rank: Unknown
timestamp: June 24, 2019, 11:24:57 am
content: Quote from: windsmurf on June 24, 2019, 04:12:23 amYou are reading too much into this. The ONLY reason I made reference to the solar system was because of the size.When you get outside the solar system, the scale of interesting things gets really big and the changes you are seeking to observe are miniscule - much finer than you can resolve - and take a very long time to show - a lot longer than your lifetime.

author: paulca
author_rank: Super Contributor
timestamp: June 24, 2019, 12:34:56 pm
content: If the gyro is accurate enough it should show the Earth rotate just more then 360 degrees in a 24 hour period, in fact roughly 361 degrees. So if you let it run from enough days to measure it, it will be off relative to the position of the sun in the sky by the number of degrees around Earth's orbit we have moved.

author: G7PSK
author_rank: Super Contributor
timestamp: June 24, 2019, 04:25:28 pm
content: If you left the gyro spinning long enough pointed at Polaris it would no longer point north as event that moves due to precession .https://earthsky.org/astronomy-essentials/north-star-movement

author: Deni
author_rank: Regular Contributor
timestamp: June 24, 2019, 04:44:34 pm
content: QuoteActually, we are - Solar system rotates around Milky Way with speed of over 828.000km/h (almost 8x faster than Earth moves around Sun)...

author: ataradov
author_rank: Super Contributor
timestamp: June 24, 2019, 04:55:18 pm
content: Quote from: Deni on June 24, 2019, 04:44:34 pmLinear movement and rotation are different things. We are moving very fast, but on a very large orbit, which makes angular changes tiny.

author: David Hess
author_rank: Super Contributor
timestamp: June 24, 2019, 06:09:27 pm
content: Wow Dave, I was going to link that based entirely on the subject but you did first.Curse your sudden but inevitable betrayal!

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 24, 2019, 09:06:49 pm
content: Quote from: David Hess on June 24, 2019, 06:09:27 pm

author: GlennSprigg
author_rank: Super Contributor
timestamp: June 28, 2019, 10:59:56 am
content: All (most?) of what was said above is thinking along 'correct' lines, except for this...Such 'Gyroscopes' are real mechanical devices, and so have Losses ! Is the example that one thinks ofspinning in Air... or sealed in a Vacuum?... They have Bearings, with friction, all-beit small. The very actsof 'trying' to change it's position adds additional lateral forces on those bearings, introducing more errors,as in an old planes gyro, as it turns, & circles the Earth. Constantly in need of correction...Do the old 'trick' of spinning a removed front bicycle wheel while it 'magically' balances while only 1 fingersupports it from just 1 end of the axle... Great... A simple Gyro effect... Notice though in reality, that youhave to keep turning yourself slowly in a circle, to maintain the illusion ? Simply system 'friction'...Such simplistic physical devices can NOT be used on Astronomical scales, or for ANY real period of Time.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 28, 2019, 08:32:49 pm
content: If an "ideal gyroscope" could be built, what exactly would be the "absolute point of reference" it would track?

author: ataradov
author_rank: Super Contributor
timestamp: June 28, 2019, 08:36:19 pm
content: Quote from: NiHaoMike on June 28, 2019, 08:32:49 pmThe one it was at when it started spinning or the last time it was set at through an external force. That's my understanding at least. This does not take into account any non-Newtonian effects.

author: Beamin
author_rank: Super Contributor
timestamp: July 21, 2019, 01:08:52 pm
content: Quote from: GlennSprigg on June 28, 2019, 10:59:56 amCould you use gyros that work against/with each other to move through zero gravity space in more then just xyz rotation actually move linearly?

author: rs20
author_rank: Super Contributor
timestamp: July 22, 2019, 09:33:11 am
content: Quote from: Beamin on July 21, 2019, 01:08:52 pmNo. You can combine two forces to make torque, but you can't combine two torques to make a linear force. This is because a torque is basically defined as two perfectly opposite forces that cancel out to leave zero net force, but there's still a twisting effect because the two forces weren't collinear.

author: ogden
author_rank: Super Contributor
timestamp: July 22, 2019, 10:10:42 am
content: Nothing is ideal, but this at least is better than mechanical spinners. Note 0.01°/hour bias uncertainty:https://en.wikipedia.org/wiki/Ring_laser_gyroscope

author: Peabody
author_rank: Super Contributor
timestamp: July 22, 2019, 02:36:25 pm
content: How would a gyro's behavior differ from a Foucault Pendulum? In a FP, the plane of oscillation rotates once every 24 hours at the poles, not at all at the equator, but somewhere in between everywhere else - the time of a complete rotation being a function of the sine of the latitude. But in theory it also measures the rotation of the Earth around the Sun, and the solar system around the galaxy, and even "absolute" movement.https://www.youtube.com/watch?v=aMxLVDuf4VY

author: David Hess
author_rank: Super Contributor
timestamp: July 22, 2019, 03:40:16 pm
content: Quote from: Peabody on July 22, 2019, 02:36:25 pmAs far as I know, they do not differ except for implementation. I was going to suggest a Foucault Pendulum as an example of a real gyro which can measure the Earth's rotation accurately.

author: Beamin
author_rank: Super Contributor
timestamp: July 23, 2019, 07:41:57 pm
content: Quote from: David Hess on July 22, 2019, 03:40:16 pmA pendulum better explained by philosophy then physics? I got lost at that part.Several in this thread have said "a gyro could measure that but the effect would be too small to notice": Do you know that for a fact or is this one of those things where people assume its common sense and just say that? I have found with common sense is that it will often lead you astray to get common place answers that are flat out wrong but because it looks like the correct answer you never question it. Why does a mirror only flip left right and not up down? Because its horizontally polarized?

author: soldar
author_rank: Super Contributor
timestamp: July 23, 2019, 07:55:04 pm
content: Quote from: Beamin on July 23, 2019, 07:41:57 pmThis is a very astute observation. Studying science and engineering is, very often, not following your "common sense" but following abstract math or other processes that are often very counter-intuitive.Regarding the gyroscope I think it is quite intuitive that if we set it spinning with its axis parallel to the axis of the Earth then, no matter how you move it, the axis will remain pointing North.

author: David Hess
author_rank: Super Contributor
timestamp: July 24, 2019, 03:41:46 am
content: Quote from: Beamin on July 23, 2019, 07:41:57 pmCommon mechanical gyros just have too much drift. If you wanted to build a gyro as large as aFoucault Pendulum, then the measurement is feasible. Large artillery and cannon also work for detecting the rotation of the Earth as they are accurate enough that their shell trajectory has to be compensated for it but a rifle you can carry is not.Gyros on aircraft and ships are slaved to a magnetic compass or other means to compensate for their drift. INS systems have to be periodically corrected.

author: Brumby
author_rank: Unknown
timestamp: July 24, 2019, 04:35:51 am
content: Quote from: Beamin on July 23, 2019, 07:41:57 pmA mirror certainlydoes notflip left and right. It merely reflects each ray of light - and does so in exactly the same manner.WhatDOESchange is the frame of reference you are applying. YOU as the observerrotate that frame of referenceby 180º around a vertical axis when you apply the left/right attributes as you would if you were facing another person, not a mirror.

author: duak
author_rank: Super Contributor
timestamp: July 24, 2019, 05:16:35 pm
content: Here's a link to a gyrocompass made from disk drive parts:https://www.instructables.com/id/Gyrocompass-Dead-Reckonator/It looks neat, but the constructor didn't fully understand the underlying principles so the rotor didn't line up north-south as expected, although it worked fine as a gyroscope. If I understand things correctly, the rotor center of mass has to be offset from the intersection of the axes and counterbalanced by a nonrotating mass. Far better fabrication skills than me though.