# How big does a mass have to be before gravity

• RandyD123
In summary, the conversation discusses the factors that determine when an object will become round due to gravity, such as compressive strengths, densities, and the force of gravity. There is no specific size that determines this, as it varies depending on the composition of the object. However, it is generally observed that icy moons become round at lower radii than stony or differentiated asteroids.

#### RandyD123

How big does a clump of rock or how big does the mass of an object have to be before gravity makes it round like a planet?

Sounds like a good exercise for learning/practicing what you know. Compressive strengths of minerals and mineral composites (rocks) run ~ 30kpsi, or 200MPa. Densities ~ 3000 kg/m3, or sp. gr. ~ 3. Pick your units. G = 6.67 x 10 -11Nm2/kg2. How large, volume or mass wise, can an accumulation of material get before surface structures crush under their own weights to less than some upper limit of radius you choose to allow for relief?

There shouldn't be a bright line - astronomical objects have different compositions, and their weight and strength depend on these compositions. But the transition region in the solar system seems to be in the 200-500 km ballpark. Icy moons tend to become round at lower radii than stony or differentiated asteroids.

The usual mentioned numbers for icy bodies is more like 400-600 km, as the Wiki ref says, while stony ones lies over that range. But YMMV.

## 1. How big does a mass have to be before gravity becomes significant?

The size of a mass does not determine the significance of gravity. Gravity is a fundamental force that exists between any two objects with mass, regardless of their size. However, the strength of gravity does depend on the masses of the objects and the distance between them.

## 2. Is there a minimum mass required for gravity to exist?

No, there is no minimum mass required for gravity to exist. All objects with mass, no matter how small, have a gravitational pull on other objects.

## 3. Can gravity exist without a mass?

No, gravity is a force that is created by the presence of mass. Without mass, there is no gravity.

## 4. Does the size of an object affect its gravitational pull?

Yes, the larger the mass of an object, the stronger its gravitational pull will be. However, the distance between objects also plays a significant role in the strength of gravity.

## 5. Is there an upper limit for the strength of gravity?

According to Einstein's theory of general relativity, there is no upper limit for the strength of gravity. However, in extreme cases such as black holes, the strength of gravity can become infinitely strong.