# Why does mass have the force of gravity?

1. Apr 2, 2007

### dhayward

1. The problem statement, all variables and given/known data
Where does mass get the force of gravity?

2. Relevant equations
F = G(m1 x m2)/r^2

F = force (N)
G = Gravitational constant (Nm^2/kg^2)
m = mass
r = distance between m1 and m2

3. The attempt at a solution

2. Apr 2, 2007

### cristo

Staff Emeritus
What's the actual question here?

3. Apr 2, 2007

### dhayward

how is the gravitational constant derived?

4. Apr 2, 2007

### denverdoc

empirically i think. In other words it is inferred from experiments/observational data and not the result of any derivation.

The holy grail in physics (and I have a completely incomplete understanding--physics is a hobby for me) is to capture all 4 fundamental forces including gravity in a superset of equations with a bare minimum of constants.

5. Apr 3, 2007

### christianjb

Are you asking why the inertial mass is equal to the gravitational mass?

6. Apr 3, 2007

### arildno

The first who carried out experiments that led to an empirical determination of G was Cavendish. By means of torsion springs, I think.

Your question can, however, be formulated in a "deep" way:

Why should an object's inherent resistance to motion change (i.e, its inertia) be in any way related to the strength of the attractive force existing between objects (i.e, gravitation)?

This identity between inertial mass and gravitational "mass" is not at all a trivially understandable relationship.