# Gravity's Effect on Mass: Exploring Its Impact

• I
• synch
In summary, gravity is a distortion of space-time that affects the path of all objects, including those with zero mass. It is not an acceleration, but rather changes what is considered a straight path. There is no specific effect of gravity on mass itself, but rather it affects all objects in the same way.
synch
(This is to check my understanding )
I gather that gravity being a space-time distortion is thought to affect everything - mass, radiation, whatever - and can be thought of as an accelerational effect.
If it is an acceleration, even entities with mass = 0 are accelerated (?).
So is there any effect of gravitation on mass, specific to mass itself ?
(Obviously a mass creates a gravitational field, that is not the question.)

I am not clear on what you are asking. Are you asking if the laws of gravity make a specific distinction between an object of 0 mass and an object of >0 mass with respect to passive gravity?

(sorry for being a little unclear)
On the basis of gravity being an acceleration via distortion in space time, any entity in such a field will be affected. So the entity does not necessarily have to have mass to be affected ( I think?), which makes me wonder if there is any specific gravity effect on mass, or is mass just something that is being affected because it is an entity that happens to be in the field. I guess the condensed question is, does gravity have an effect on mass, specific to mass as opposed to anything else.
(I hope that makes sense)

synch said:
On the basis of gravity being an acceleration
It isn't. A key realisation of relativity was that free-falling bodies aren't accelerating. It's those of us standing on the surface of the Earth or in a rocket under thrust who are accelerating - we are being pushed out of our free-fall paths by the floor, for one reason or another.
synch said:
I guess the condensed question is, does gravity have an effect on mass, specific to mass as opposed to anything else.
Mass is a property of things, not a thing itself. So I think you mean "does gravity have a different effect on objects with non-zero mass compared to those with zero mass".

The short answer to that is yes and no. Qualitatively the effect is the same: the "straight line" that things travel in naturally becomes a geodesic, which generally has a curved spatial component, when there is a gravitational field. That is true for everything. When you get into the detailed maths, you find a couple of extra terms in the equations for the paths of massive bodies. That's not really surprising since massless objects must move at c and massive ones cannot, so of course their paths are different. It does have an effect on where orbits are possible - massless bodies can only have circular orbits around non-rotating black holes at 1.5 times the Schwarzschild radius, while massive bodies can have circular orbits at any radius above this (although they are only stable above 3 times the Schwarzschild radius.

Note that all the above is for test particles whose gravity is so much weaker than whatever they are orbiting that it can be ignored. The way that gravitational source terms other than mass enter the equations of general relativity is quite different from how mass does. I don't know a lot about that.

synch said:
(This is to check my understanding )
I gather that gravity being a space-time distortion is thought to affect everything - mass, radiation, whatever
More precisely, it changes what we should think of as a straight path. The curvature of space-time due to gravity causes a bend in what is straight in space-time (a geodesic). So anything that moves, will move differently. It's like the surface of a globe changes the shortest path between two cities.
- and can be thought of as an accelerational effect.
It's really the opposite. What Newton thought of as acceleration due to gravity is thought of in GR as following a straight space-time line (geodesic) with no acceleration.
If it is an acceleration, even entities with mass = 0 are accelerated (?).
Anything following a geoesic may look curved in space by the old, Newtonian thinking.
So is there any effect of gravitation on mass, specific to mass itself ?
No. You should not think of it that way.
(Obviously a mass creates a gravitational field, that is not the question.)

Thanks ! excellent and very helpful replies

## 1. What is the relationship between gravity and mass?

The more massive an object is, the stronger its gravitational pull. This means that objects with larger masses will attract other objects with a greater force.

## 2. How does gravity affect the mass of an object?

Gravity does not directly affect the mass of an object. Mass is a measure of the amount of matter in an object, while gravity is a force that acts upon objects with mass.

## 3. Does gravity have any impact on the weight of an object?

Yes, gravity does have an impact on the weight of an object. Weight is a measure of the force of gravity acting on an object. So, the greater the gravitational pull, the greater the weight of the object.

## 4. How does gravity impact the movement of objects with different masses?

Objects with larger masses will experience a greater force of gravity, causing them to accelerate at a faster rate. This means that objects with different masses will fall towards the ground at the same rate, regardless of their mass.

## 5. Can an object's mass affect the strength of gravity?

No, an object's mass does not affect the strength of gravity. The strength of gravity is determined by the masses of two objects and the distance between them. However, the larger the mass of an object, the greater its gravitational pull will be towards other objects.

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