physics question

[DotCommunist]

could ask google but you lot have a crack. Is my understanding here correct. Spin imparts stability. That's why we have rifling in guns, spin bowlers and fletching on arrows.

When you spin the bucket of water on a rope around and it stays in this is centrifugal force yes. But you are stationary relative to the larger gravitational mass, the massive planet. Is it then the case that by imparting spin to an object you stabilise it because it is now benefiting from that same 'relative to the more massive object' by spinning?

 

[mrs quoad]

Isn’t, what.

Isn’t the.

Hmm.

I’m not sure about how this is operationalised.

Gyroscopes work in space.

If you’re spinning your bucket fast enough, and had an ejector seat, you would be totally stable in your trajectory. I think.

If you were above a big ol fat ass earth, and were shot across it, then I think you’d be stabilised in some sort of fucked up parabolic arc.

If you weren’t, I think you’d just fuck off for ever in the same direction, stably and consistently.

Ianaphysicist, mind.

I don’t think we’ve had one since perplexis left. Have we?

 

[mrs quoad]

Also, flat earth says #fuckrightoffwithyourglobalassumptions.

And bollocks to Newton, too. The wanker.

 

[DotCommunist]

Gyroscopes work in space.

near space being notoriously unaffected by massive planets. But you see my conundrum. Why does the spinning object have greater accuracy.

 

[toblerone3]

 

[Winot]

I think your two examples are different. Spin resulting in stability of bullets etc. is due to Bernoulli effect, isn’t it?

 

[Athos]

Spin bowlers don't impart spin to increase stability.

 

[pocketscience]

rotational (angular) kinetic energy - i.e the torque of the spinning object vs the energy of the stationary mass of a tensor object (if I understand your question correctly - plus it's been a very long time since I endured physics lectures on this)

for your examples the effects of (planetary) gravity is negligible to non existent

 

[pocketscience]

also, fletching causes the arrow not to spin and provides stability (linear kinetic energy)

 

[mrs quoad]

But you see my conundrum. Why does the spinning object have greater accuracy.

I think the question is wrong, and suspect that (amongst other things) spinning very ducking fast would ensure that uneven drag from minuscule imperfections on a bullet’s surface weren’t catastrophically exaggerated over its course between the end of a rifle barrel and its target 170 metres away.

I suspect the bigness of the world is trivial compared to drag.

And I’m not sure it has much of a role to play compared to gyroscopic forces, either, if they’re relevant.

Which I think they are, because otherwise, bicycles: no.

 

[mrs quoad]

Also: golf balls.

Dimpled because air.

Not dimpled because gravity.

I think.

 

[2hats]

Why does the spinning object have greater accuracy.

Spin stabilisation, through conservation of angular momentum, maintains the orientation in space and thus preserves aerodynamic profile presentation relative to the oncoming airflow.

 

[Saul Goodman]

also, fletching causes the arrow not to spin and provides stability (linear kinetic energy)

Not to be confused with felching.

 

[pocketscience]

Not to be confused with felching.

 

[pocketscience]

Spin stabilisation, through conservation of angular momentum, maintains the orientation in space and thus preserves aerodynamic profile presentation relative to the oncoming airflow.

Why isn't spin stabilisation used on darts or conventional arrows?

 

[2hats]

Why isn't spin stabilisation used on darts or conventional arrows?

I'm no archery expert, but I think there are some types of arrows with helical fletching to spin stabilise them to some degree.

Would be much harder to do with darts as the manual release technique needed to spin them up is probably more prone to leading to tumbling and loss of accuracy?

 

[pocketscience]

I'm no archery expert, but I think there are some types of arrows with helical fletching to spin stabilise them to some degree.

Would be much harder to do with darts as the manual release technique needed to spin them up is probably more prone to leading to tumbling and loss of accuracy?

Thanks, & sorry I was too lazy to google.
This site suggest that helical fletching does indeed lend to accuracy in archery (so I guess to some degree more stability)

 

[squirrelp]

Spin bowlers don't impart spin to increase stability.

Very true.

However, for swing bowling, a fair amount of backspin is necessary to keep a seam orientation stable (otherwise the seam 'wobbles').

 

[moon]

It always amazes me that we are all currently spinning at 1000 miles per hr... I kind of get a bit giddy thinking about it and wondering what would happen if the earth suddenly stopped spinning, would we all be flung out into space??

 

[NoXion]

It always amazes me that we are all currently spinning at 1000 miles per hr... I kind of get a bit giddy thinking about it and wondering what would happen if the earth suddenly stopped spinning, would we all be flung out into space??

As I understand it there are various physical properties that are always conserved within a closed system, the one most relevant in this case being angular momentum. So all of that massive amount of energy bound up within the Earth's rotation can't be destroyed or deleted, it must go somewhere. Being turned into heat is most likely. According to this table, the rotational energy of the Earth is equivalent to 210,000,000,000,000,000,000 gigatons of TNT. So depending on how fast the energy transfer happens, the effects could range from "slightly elevated infra-red emissions into space", "devastating planetary warming", "God help us the oceans are boiling and everything is on fire" and finally an explosion big enough that we wouldn't have to worry about anything ever again.

 

[2hats]

It always amazes me that we are all currently spinning at 1000 miles per hr... I kind of get a bit giddy thinking about it and wondering what would happen if the earth suddenly stopped spinning, would we all be flung out into space??

That depends on precisely what you mean by Earth (the surface, surface plus core, those plus oceans, those plus atmosphere) and the time scale over which you propose this happening. Also, stopped rotating relative to what?

Very long term (billions of years) the Earth's rotation rate will slow until it is locked synchronously with the Sun, for (one real) example.

 

[2hats]

As I understand it there are various physical properties that are always conserved within a closed system, the one most relevant in this case being angular momentum. So all of that massive amount of energy bound up within the Earth's rotation can't be destroyed or deleted, it must go somewhere. Being turned into heat is most likely. According to this table, the rotational energy of the Earth is equivalent to 210,000,000,000,000,000,000 gigatons of TNT. So depending on how fast the energy transfer happens, the effects could range from "slightly elevated infra-red emissions into space", "devastating planetary warming", "God help us the oceans are boiling and everything is on fire" and finally an explosion big enough that we wouldn't have to worry about anything ever again.

If you were able to stop the planet rotating suddenly, aside from immediate horrific consequences at the macro level for all its inhabitants, it would spin up again anyway (demo: try this with a fresh, uncooked egg on a flat surface ie spin it then stop it by briefly touching it then observe what happens).

 

[NoXion]

If you were able to stop the planet rotating suddenly, aside from immediate horrific consequences at the macro level for all its inhabitants, it would spin up again anyway (demo: try this with a fresh, uncooked egg on a flat surface ie spin it then stop it by briefly touching it then observe what happens).

I was more thinking along the lines of if one had the ability to suck the rotational energy out of an object at an arbitrary rate and convert it into something else. So rather than stopping the spinning egg with your finger, you have a technomagical device that could convert the energy involved into heat, say. So the egg ends up no longer spinning, but is now instead warmer by however much energy was involved. If that makes any sense. I've had a few skinfuls this evening.

 

[2hats]

what would happen if the earth suddenly stopped spinning, would we all be flung out into space??

To flesh this out a bit more…

Scenario A: rocky crust/solid core of Earth stop spinning immediately => habitats destroyed by atmosphere and oceans still moving at aforementioned speed, scouring the surface of the planet.
Scenario B: everything (crust, mantle,core, oceans, atmosphere) stops together => relative position of Earth fixed in space so the Sun only ‘moves around the Earth’ once per year. Hence a very hot sunward hemisphere and an opposite very cold deep space facing hemisphere. The lack of rotation would also lead to reduction in the oceanic equatorial bulge (several km difference from the poles) which would mean ocean water migrating to the poles, land appearing around the equatorial regions and higher latitude countries being flooded (in the hemisphere where the ocean hadn’t frozen). Additionally with no rotation of the Earth’s outer core the magnetic field would be negligible which means higher levels of cosmic rays and accelerated evaporation of the atmosphere eventually leading to no UV protection and no breathable atmosphere (see Mars for results).

However, one thing would stop the above from playing out - the Moon is still in orbit about the Earth so, due to conservation of angular momentum and the Earth Moon tidal interaction, the Moon would simply spin the Earth back up again with relatively minor disruption (compared to scenarios A, B) to atmospheric and biological systems, which would adapt anyway (note: the Moon would stop drifting away from the Earth in the process).

 

[High Voltage]

I was more thinking along the lines of if one had the ability to suck the rotational energy out of an object at an arbitrary rate and convert it into something else. So rather than stopping the spinning egg with your finger, you have a technomagical device that could convert the energy involved into heat, say. So the egg ends up no longer spinning, but is now instead warmer by however much energy was involved. If that makes any sense. I've had a few skinfuls this evening.

You do realise that you've, basically, just invented the self boiling egg.

So, tell me more about this technomagical device of yours, it sound just the kinda thing I'd like to invest in

 

[teuchter]

could ask google but you lot have a crack. Is my understanding here correct. Spin imparts stability. That's why we have rifling in guns, spin bowlers and fletching on arrows.

When you spin the bucket of water on a rope around and it stays in this is centrifugal force yes. But you are stationary relative to the larger gravitational mass, the massive planet. Is it then the case that by imparting spin to an object you stabilise it because it is now benefiting from that same 'relative to the more massive object' by spinning?

I think the answer to your question is "no" but check out Mach's principle.



This does my head in a bit.

 

[moon]

Thanks for all the replies, the self boiling egg sounds fascinating, maybe you invented a new harvestable energy form there

So would I be right in thinking that as well as the earth spinning the universe is also spinning??

 

[2hats]

would I be right in thinking that as well as the earth spinning the universe is also spinning??

Recent measurements suggests the universe is not spinning - it appears to be isotropic.

 

[moon]

i wonder how they take the measurement..
I have loads more physics questions by the way. But it's nearly xmas sooo I will get back to you on that.
But they are related to negative space, photosynthesis and protein folding etc..

 

[NoXion]

You do realise that you've, basically, just invented the self boiling egg.

So, tell me more about this technomagical device of yours, it sound just the kinda thing I'd like to invest in

It comes from the same supplier that does those perfectly spherical cows.