Why are two objects with mass drawn to each other?

Gravitational force -an attractive force that exists between all objects with mass; an object with mass attracts another object with mass; the magnitude of the force is directly proportional to the masses of the two objects and inversely proportional to the square of the distance between the two objects.

Explanation:

Objects with mass attract each other because of gravity. Gravity is caused by the attraction of objects with mass. Mass does not attract mass, but rather spacetime is curved. You could even argue there is no mass, its all just energy.

Explanation:

heat the gas and measure the pressure