Gravitational Force: Sun vs Earth

[atomant]

Which, if either, is greater: the gravitational force of the sun on the Earth, or the Earth on the sun? How should I be looking at this question i.e in terms of the radius of each object through the equation F=GM1M2/r^2 ?

 

[pmb_phy]

Which, if either, is greater: the gravitational force of the sun on the Earth, or the Earth on the sun? How should I be looking at this question i.e in terms of the radius of each object through the equation F=GM1M2/r^2 ?

They're the same, i.e. wherever there is an action there is an equal and opposite reaction. You should look at the symmetry of F=GM1M2/r^2.

Pete

 

[atomant]

So it's the same because the G is constant or because the r^2 is the same for bothe planets?

 

[Eivind]

Newtons third law, F=-F.

 

[atomant]

right, and if we were to calculate the the gravitational force exerted on the Earth by the sun we would use F=GMm/r^2.
If so I know G is constant, but what values do we substitute for the masses M and m? mass of Earth and sun?

and if we were to find the gravitational force exerted on the sun by the Earth, how do the values change?

 

[Eivind]

Yes, use GMm/r^2. For M you use the suns mass, and for m use the Earth's mass. r^2 is the distance sun-earth. The gravitational force exerted on the Earth by the sun, is eqvivalent whit the force the Earth exerts on the sun.
Let`s say F, is the force from sun to earth. Then -F is the force from Earth to sun.