Gravity

[Crowbob]

So any object that has mass has gravity, right? The more mass, the more gravity.

So my question involves a scenario wherein there is a spherical open space at the center of the earth, somehow. Would an object in that sphere be weightless?

[A930Rocket]

I have no idea, but I would think the center of the earth just keeps getting smaller and smaller and smaller with gravity. If you were reduce the sphere by 50% you have gravity, if you do it again you have gravity, etc. to infinity.

[sc_rufctr]

In theory: If there was a shaft drilled right through the center of the Earth... And you fell into that shaft you would "Slinky" (assuming you didn't hit the sides of the shaft) until at some point you'd be suspended at the exact center of mass of the Earth.

[Bob Kontak]

Originally Posted by Crowbob

Would an object in that sphere be weightless?

It would be impacted by the mass "above". Dead center it would float given a weight balanced sphere. It would not be weightless. It would not have an overriding vector to initiate movement

Not like Einstien's guy falling off a roof where he is weightless.

[flatbutt]

Standing at the North Pole all directions are South. Similarly, at the center of the Earth all directions are up. So, your body is being acted on from all directions equally. You may feel weightless but there is definitely gravity there.

[herr_oberst]

Originally Posted by flatbutt

Standing at the North Pole all directions are South. Similarly, at the center of the Earth all directions are up. So, your body is being acted on from all directions equally. You may feel weightless but there is definitely gravity there.

Weightless or "weightful". Imagine standing on your head, (or suspended by your ankles) your blood rushes to your head, you're not used to it. Wouldn't it be that at the center of the earth, 360 degree gravity would be trying to pull you apart from every direction?

I don't know, just trying to imagine.

[Arizona_928]

Originally Posted by flatbutt

Standing at the North Pole all directions are South. Similarly, at the center of the Earth all directions are up. So, your body is being acted on from all directions equally. You may feel weightless but there is definitely gravity there.

Gravity from others. Ie moon and tides

[Steve Carlton]

I was there last summer. My acid reflux was very unpleasant.

[island911]

First, you would hit the sides. Coriolis - even if through the poles...

Gravity is an acceleration. F=ma or F=mg

When accelerations are balanced - like falling due to gravity that acceleration a=g (weightless, but not massless)

So, you reach terminal velocity on the way down that changes as the air gets thinner, fly back up the other side a ways, and oscillate about the center for a while dead from a lack of O2

[Bill Douglas]

It would be pushed from all directions. So weightless on a set of scales. It would be like your head after drinking too much - feels like it's being crushed from all directions.

Disclaimer: I failed physics at school.

[island911]

IIRC you can look for gravity distribution as "peak gravity" ... some say it is at peak a few miles down due to the earth crust being relatively spongey. Where as our iron core is massively dense. - the crust puts us 'out in orbit a bit, so to speak.

Edit: look for "peak gravity earth crust"

[hk968]

> Would an object in that sphere be weightless?

Yes, it would be weightless anywhere inside that hollow sphere.

See here: https://en.m.wikipedia.org/wiki/Shell_theorem

[Pazuzu]

There are lots of geometries where you can find zero-gravity regions and high-gravity regions. A cylinder of material has gravity on the outside surface, but not the inside surface. If that cylinder was spinning along it's axis, then there would be false gravity inside, on the inner edge, and the false gravity would get smaller as you got closer to the center of rotation. The same rotating cylinder could now have zero "effective" gravity on the OUTSIDE, if you spun it just right.


So many weird things. Why would you be concerned about gravity in an empty shell in the middle of the Earth?

[Steve Carlton]

He's asking for a friend.

[Crowbob]

Originally Posted by Pazuzu

There are lots of geometries where you can find zero-gravity regions and high-gravity regions. A cylinder of material has gravity on the outside surface, but not the inside surface. If that cylinder was spinning along it's axis, then there would be false gravity inside, on the inner edge, and the false gravity would get smaller as you got closer to the center of rotation. The same rotating cylinder could now have zero "effective" gravity on the OUTSIDE, if you spun it just right.


So many weird things. Why would you be concerned about gravity in an empty shell in the middle of the Earth?

Mostly I’m concerned because somebody else is already tackling the searing questions about what happened millions of years ago and billions of light-years away.

But also, my calculations didn’t look right. If the universe is expanding and everything in it is moving away from everything else at ever-increasing speeds, I was wondering if there is a center of it and what that center might look like. My intuition told me there can only be such an expansion if such a center has zero mass. Gravity, being a function of the mass of objects and their distances from each other, means that in order for expansion to occur one of the variables in the equation must be zero. Since the distance between objects cannot be zero, somewhere there must be no mass, which, as I suspected, would be the center.

Then I fell asleep.

[LEAKYSEALS951]

Being in the exact center of earth makes your eyes bulge- gravity pulls them out in every direction.

[aschen]

Yes approximately weightless at the center of the earth but precisely very hot

[Steve Carlton]

I found this: https://www.forbes.com/sites/startswithabang/2021/01/05/how-is-the-universe-accelerating-if-the-expansion-rate-is-dropping/?sh=6bca414d4093

Then got sleepy.

[Bill Verburg]

Originally Posted by Crowbob

So any object that has mass has gravity, right? The more mass, the more gravity.

So my question involves a scenario wherein there is a spherical open space at the center of the earth, somehow. Would an object in that sphere be weightless?

mass is a property of matter

gravity is a force that interacts w/ mass and obeys the inverse square relation where the effect of the closest and largest mass has by far the most effect.

unbalanced forces cause acceleration

the earth isn't a sphere, it is an oblate spheroid but if a motionless mass were placed at the center of a theoretical hollow sphere of uniform mass all the local gravitational forced would sum to zero. However the non local gravitational forces would still be present and in the universe we live in w/ distributed mass concentrations, at random distances and directions, these would not sum to zero

there are places in the real universe where all the gravitational forces sum to and effective zero for long enough periods of time, these are called LaGrange points.

The math gets really complicated but for a 2 body system, say, like the Earth and moon there are 5 LaGrange points

[Crowbob]

Yeah, I guess I was using ‘mass’ when I should have used ‘matter’.

So let’s assume the universe averages out to equal matter in all directions from it’s center. Meaning, amongst all the infinite LaGrange points is one primary point at the very center.

Because the validity of my calculations have been corroborated here on PPOT, I shall henceforth call it the Crowbob LeGrange because, of course, everybody knows and has thus been proven, the universe revolves around me.

Any further questions or observations?