# What's gravity good for?

Discussion in 'Physics & Math' started by arfa brane, Dec 28, 2016.

1. ### arfa branecall me arfValued Senior Member

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When you climb a hill or mountain, you're allowing for the local topography, you're on the surface and so you have to move up and down over any wrinkles in it.

A plane flying straight ahead through the air doesn't have to account for local topography by moving up and down like you on the surface have to.

This is because:

* gravity smooths out the plane's local frame of reference;

* the atmosphere smooths out the plane's local frame of reference;

* it's for the same reason you don't have to walk at an angle climbing a hill, and the reason you can't walk straight up a cliff sideways;

* it's because the force of gravity restores a local symmetry, gravity acts everywhere on the surface as if from the centre of the earth, not points on its surface.

?

3. ### SeattleValued Senior Member

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*it's because it's above all of the ground base objects...

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5. ### iceauraValued Senior Member

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It's because the plane can launch itself through the air, whereas if you try that with dirt and rocks you will break your nose. Not even the plane can do it.

What gravity does is keep all the dirt and rocks in position. Also, if you drop anything you know where to look for it.

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7. ### Michael 345Bali in Nov closerValued Senior Member

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Planes flying over the surface of the world detect variations in gravity according to what surface they are flying over.

More mass more gravity.

However while the gravity does vary, and the plane does move on account of gravity changes, the movements are to small to be felt by passengers.

Instruments detect and record small gravity changes which can be interpreted to find minerals.

Humpty Dumpty knows all about the attractive force of gravity.
Poe knows he is attractive

8. ### danshawenValued Senior Member

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The force hierarchy problem assures that the gravitational pull of something as large and as dense as a mountain is minuscule compared to the mass of the Earth. The center of mass of the Earth is not shifted skyward very much even by a mountain as massive as Mt. Everest.

Besides which, you still need to worry about the topological problem and dynamics of flying into the side of one of those. In a contest between the mechanical forces that can be exerted by something with as much inertia as a mountain and a light aircraft, the mountain almost always wins.

Gravity therefore is only part of the issue of why still calm air is fairly smooth flying. Try bucking the jet stream and your experience may be a little different. Large convection air currents which often occur near mountains or even the edges of dense clouds during daylight hours is another set of issues seemingly not taken into account in your scenario. The turbulence produced by these effects is not caused by gravity either, but the turbulence you experience may also be related to the mass of the aircraft.

Last edited: Dec 28, 2016
9. ### danshawenValued Senior Member

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And how exactly does a flying aircraft or a falling projectile even know what 'symmetry' is (which direction to fall)? Parts of it may continue falling down the side of a steep mountain after it has crashed. How does it know to do that? That likely won't be a very smooth trajectory either, but not because of an averaging or smoothing of local gravity.

10. ### danshawenValued Senior Member

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Yes, but usually that is not where you find whatever you dropped, particularly if it was something small and bouncy.

11. ### exchemistValued Senior Member

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None of the above. It's because a plane's trajectory does not encounter physical obstructions on the Earth's surface. Gravity is neither here nor there. If there were no gravitation and you were able to hover weightlessly at the Earth's surface, you would still have to go up and down to avoid obstacles. Why do you see the need to make this complicated? Or are you taking the piss out of someone and I've missed the joke?

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12. ### SeattleValued Senior Member

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Exchemist...that's always hard to figure out on this site.

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13. ### arfa branecall me arfValued Senior Member

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Quite. Well, a plane isn't "on" the surface. But to support your argument, I think you need to cover how the atmosphere is independent (somehow) from the surface and presents no physical obstruction to the plane's trajectory.

As to the joke aspect, I saw someone ask what use is GR, and I figured someone might as well ask what use is gravity, and, here we are.

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14. ### RuneSpiderRegistered Senior Member

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Atmosphere is seperate from the surface by being composed of less dense material.
And it does present a physical obstruction, chiefly air resistance. Part of the reason engines on the plane have to keep going.

15. ### The GodValued Senior Member

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Thats quite smart. Do you need any additional humor when likes of retired chemists are around who are Poking their funny nose everywhere without an iota of knowledge.

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Not sure about retired chemists, but how about brotherly directors of some remote Indian company, continually conducting evangelisitic crusades on public forums being the only outlet they have?

17. ### The GodValued Senior Member

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It will take a lot of time for you to get over with Rpenner showing you the mirror in that GR thread. This post best describes your mentality. Try to forget your ex screwer.

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The evidence is here for all to see my friend, and if you need to see any screwing, then pop over to cosmoquest and see how he faired over their.

ps: I would also suggest you take heed of the mirror that rpenner showed you, lest you want another holiday.

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Yes, amazing how naive and stupid some people can be, particularly when burdened with a religious agenda.

20. ### gmilamValued Senior Member

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What's gravity good for?

It keeps my beer from floating out of my glass.

21. ### arfa branecall me arfValued Senior Member

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Just another thought on gravity and frames of reference.

An ant can easily climb a vertical cliff face, humans can climb them if there are sufficient hand and footholds. The ant finds plenty because it sees a much rougher surface, but the main reason an ant can climb with about the same effort as walking forward is:

* being smaller, it has much greater relative strength in its leg muscles;
* gravity interacts much less with an ant than with a human;
* muscular strength doesn't scale between ants and humans.

22. ### Michael 345Bali in Nov closerValued Senior Member

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Surely as per mass gravity acts same proportional wise?

Humpty Dumpty knows a bit about gravity.
Poe floats

23. ### arfa branecall me arfValued Senior Member

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If by that you mean acceleration is identical regardless of the mass, or, both a human and an ant will fall at the same rate, then yeah.

Gravity keeps pointing in the same direction for ants and humans, neither gets to decide if a force is pulling them backwards instead of downwards, physics makes the choice.

Ergo, you can't lie on your back and claim to be walking up a cliff.

Just sayin'

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