Gravity
 

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?

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.

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.

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.

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.

Gravity from others. Ie moon and tides

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

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

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.

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"

> 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

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?

He's asking for a friend.

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.

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

http://forums.pelicanparts.com/uploa...1673878417.jpg

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

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.

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

https://i.stack.imgur.com/aM9L5.jpg

https://i.stack.imgur.com/eXWhr.jpg

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?

Astronauts orbiting earth are weightless because they are in free-fall while orbiting earth. The spaceship is also weightless for the same reason. Earth is orbiting the sun, just as a spaceship orbits earth. Therefore, Earth is weightless. So if you can be at the exact center of Earth's mass, you are weightless. I'm ignoring other gravitational "forces" - gravity is not a force - like the pull between Earth and Moon, and the fact that orbits decay.

Is this correct? I just came up with this theory. But it makes sense to me.

Isn't it kinda hot down there?:D

Gravity is not a force. Gravity is an acceleration that can produce a force. F_g=mg

Not this guy's best vid, but, fwiw.

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We understand the gravity from acceleration, but still don't know just how two objects actually apply forces to each other through a vacuum at millions of miles distance. Think of our sun, 92 million miles distance, and it keeps us in orbit. Otherwise we would fly off into space and all die from cold.

https://en.wikipedia.org/wiki/Graviton

Gravitons are one possibility, but we can't yet figure out how. Yet one thing for certain, gravity always works, and it is nice to know that in the morning when you put your foot out of bed it will go down, and not up to the ceiling 100% of the time.

Many good YouTube videos on this subject. Maybe slightly OT - but gravity travels at the speed of light.

Kola Superdeep Borehole. 7.6 miles deep.
You wouldn't want to fall in.

https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole#:~:text=In%20terms%20of%20 depth%20below,deepest%20artificial%20point%20on%20 Earth.

And it is just 3,959 on average to the center of the Earth. Just 3,951.4 miles to go!

The the tunnel that goes through the Earth is going to be just under 8,000 miles of tunnels. Not anytime soon.

IDK, maybe if CA wants a high-speed rail system to that location. (shrug)

oops, sorry for the dig.

I think the opposite of Earth from California is the ocean out close to Madagascar. Not a big demand to travel to and from there.

you have that backward

the only way to produce an acceleration on a mass is to apply a force

per the current version of the Standard Model
there are only 4 forces all are mediated by their respective Bosons

not counting dark mass and dark energy

there are only 2 broad categories which make up the universe
Fermions which make up all the mass and Bosons which mediate all the forces

mass is a scaler property which arises from the Higgs particle which is a scaler Boson arising from a scaler field permeating the Universe, all other Bosons are gauge Bosons

gravity effective at large distances per the inverse square law, things become muddled at the ultra short distance like inside an atom, a more inclusive model is needed, only an attractive force, mediated by the not yet detected but hypothesized Graviton, strength scale wrt electro-magnetism 10exp-61

electro/magnetic also effective at large distances per the inverse square law, both attractive and repulsive, mediated by the zero mass gauge Boson called a Photon, strength scale 1


weak nuclear only effective at very short ranges, responsible for radioactive decay, mediated by massive gauge Bosons , W+, W- and Z, strength scale 10exp -4

strong nuclear hold atom together, mediated by the Bosons called Gluons, strength scale x60, has asymptotic freedom, ie can never exist outside the nucleus(in the current universe, at one time immediately after the big bang everything was like the nucleus ie a quark-gluon soup)

Do I?

Newton was right, Einstein was wrong?

Your explanation of how F_g=mg=ma (g=a) "is backwards" seems a bit non sequitur and does not flip these relationships. Not even in Newtonian physics.

And I'm fairly certain that the Higgs particle got squished down the drain buy Higgins. :cool:

So, the unified theory will have to wait.

Gravity sucks!

Destroyed my dream of dunking a basketball :(

excuse me,:confused:

Perhaps you need to go back to school for a refresher

basic Physics 101 a force is what causes a change in motion(aka acceleration)

both Newton and Einstein are right w/i certain restrictive domains

Newton was right for large objects moving relatively slowly in relatively weak gravitational fields

Einstein merely refined Newton to explain and describe mathematically w/ fewer restrictions

neither was totally right for all possible scenarios

a major failing of Newton was his ability to describe the orbit of mercury accurately enough, mercury is in a gravitational field just strong enough and is moving just fast enough that Newtons math failed, Einstein corrected that to an exquisite degree that has not been seen to err

Einstein's math fails at very small scales, approaching the Plank distance, here Quantum Theory is necessary to describe what is going on, which it also does exquisitely.

The conundrum of modern Physics lies in reconciling Einstein and Quantum Theory

String Theory and Quantum Gravity being the most promising paths

That is totally incidental and not really relevant to basic forces and accelerations in the usual realms of earth, moon planetary or even large scale Galactic motion

Gravity puts a curve in space, right? Straight as the Crowbob flies, basically.

@ which point did they park the J Webb Telescope?

There are several ways to look at and describe how gravity works and mass causing a geometric deformation of space-time is one of them


similarly there are different ways to look at how photons work
one is to think of them as particles and the other as waves, each is able to describe certain events that the other can't

That is why Quantum Theory is so powerful because it combine wave/particle duality in a way that as perfectly as we can determine describes reality

This is all so very interdastink.

Nobody answered my question in post 22
I'm really wondering because I have to dig a hole this summer.

There many different Lagrange points, described by various mass doublets,

For the Earth-Moon system the Webb is parked at L2 beyond the far side of the moon

keep in mind that there are still other perturbations from other bodies, mainly the Sun and Jupiter