# Crash course on black holes

1. Nov 22, 2013

### taonut

Hi,

2. Nov 22, 2013

From where did you find this statement?This is wrong.

Mass is the amount of matter present in a substance

Usually we assume that Force of gravity acts on the center of mass of the object.(To make calculations easier)
Stars does not spin around empty space.Inside stars,there is the core of it.

We know Earth has mass because it causes gravity.

Anything which has mass will cause gravity

Force of gravity between two masses, $F=\frac{Gm_1m_2}{r^2}$
Where m_1 and m_2 is the masses of two objects.
G is the Universal Gravitational Constant
r is the distance between two object

3. Nov 22, 2013