# The Naked Scientists Forum

### Author Topic: Is gravity caused by the spin of an object?  (Read 1169 times)

#### flysci

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##### Is gravity caused by the spin of an object?
« on: 27/02/2016 18:14:01 »
I'm not a professional scientist or mathematician, so I'm not able to express myself with scientific terminology, but I've been thinking about this for a while and was just wondering if anyone could tell me whether any part of my thinking has any merit.

My thoughts are:

Rather than gravity being a force in its own right, could it just be the difference between the attractive force of a spinning body and the repulsive centrifugal force of the particles spinning around it?

What I mean is, could all spinning bodies have an entity at the centre pulling particles towards it and when anything spins around it, the centrifugal force of those particles repels them from the central entity hence creating the differential we call gravity?

In a bit more detail:

Could there be an entity at the centre of all spinning bodies that possess a gravitational effect, that creates an attractive force e.g. a black hole or something else, which is either only created once a body starts spinning or the cause of a body to start spinning?

Then, once that body starts spinning, the particles that are attracted to it spin around the centre. The speed of circulation creates a centrifugal force, which is a repulsive force against the attractive force of the entity at the centre of the spinning body.

The difference between the attractive force and the repulsive force is what we call gravity.

It could also be that the attractive force is greater than the repulsive force, the closer a particle is to the centre of a spinning body that has gravity, but weaker the farther away it is. This would mean that the closer a particle is to the centre, the faster the particle will need to travel to maintain the same orbit and vice versa, the farther away a particle is from the centre.

A bit like how a satellite stays in orbit, if its speed matches the earth's attractive pull, but will tend to fall to earth if it slows down or escapes from earth if it speeds up.
« Last Edit: 28/02/2016 09:58:22 by chris »

#### Ophiolite

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##### Re: Is Gravity just the difference between
« Reply #1 on: 27/02/2016 18:58:33 »
We can detect and measure the gravitational attraction of a mountain. How would your hypothesis explain that.

#### Bored chemist

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##### Re: Is Gravity just the difference between
« Reply #2 on: 27/02/2016 19:35:30 »
Gravity works with things that are not spinning (at least in a macroscopic sense).

#### evan_au

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##### Re: Is Gravity just the difference between
« Reply #3 on: 28/02/2016 09:43:03 »
Quote
could (gravity) just be the difference between the attractive force of a spinning body and the repulsive centrifugal force of the particles spinning around it?
Yes, there is a difference in weight due to rotation. If the Earth had the same mass and the same shape, but was not spinning, your weight measured at the equator would be greater.

(You actually would not want to try this experiment, because it would set of a series of massive tsunamis and earthquakes, because the "geoid" - the surface of the continents and the oceans already balances the effects of gravity and rotation - but that is for another time.)

Quote
could all spinning bodies have an entity at the centre pulling particles towards it
Yes, there is a point at the center of a spherical object from which the gravity acts as if originates (as seen by any object outside the sphere).

If you look at Cavendish's original laboratory experiment to measure gravitation, it used spherical lead balls. Crucially, these lead balls were not rotating around their axis (from the viewpoint of someone standing in the laboratory). So gravity applies to all objects, whether they are rotating or stationary.

It also applies to objects whether they are spheres or not - but the maths is a lot easier if you use spheres, especially if they have uniform density. And most objects large enough to have a human-noticeable gravity will be in the shape of a sphere.

Quote
Could there be an entity at the centre e.g. a black hole
If there were a black hole at the center of the Earth, it would eat the Earth from the inside. The bigger the black hole, the faster it eats.
However, you don't need a special entity - ordinary matter creates a gravitational field, purely due to its mass.

Quote
This would mean that the closer a particle is to the centre, the faster the particle will need to travel to maintain the same orbit and vice versa, the farther away a particle is from the centre.
You need to distinguish two distinct scenarios here:
• Outside the sphere: The gravitational attraction decreases as the square of the distance from the center. This is Newton's "Inverse square law". It is true that in this scenario, a satellite orbiting the Earth has a faster orbital velocity the closer it is to the (center of the) Earth.
• Inside the sphere: The gravitational attraction is determined by the mass that is closer to the center than you are (any mass farther than the center cancels out in all directions). The closer you get to the center, the less mass is between you and the center. As you get closer to the center, the gravitational attraction decreases, and the slower the orbital speed. Right at the center is weightless.

He did not need to rotate the lead balls.
Gravity is a property of all matter, not just some "special" kind of entity.

#### The Naked Scientists Forum

##### Re: Is Gravity just the difference between
« Reply #3 on: 28/02/2016 09:43:03 »