Newton's universal law of gravitation
F = (G * m1* m2)/d^3
Where:
F = force
G= universal gravitation constant
M1= mass 1
M2 = mass2
d = distance
The force of attraction is directly proportional to the product of their masses.
40 x 2 = 80 N
If the mass of one object is doubled, then the force is doubled.
