# Understanding Newton's Law of Universal Gravitation

1. Oct 14, 2007

### Ecterine

"Consider the earth following its nearly circular orbit about the sun. The earth has a mass mearth=5.98x10^24kg and the sun has mass msu=1.99x10^30kg. They are separated, center to center, by r=93 million miles = 150 million km."

What is the size of the gravitational force acting on the earth due to the sun?

I'm still setting up the problem...

I think I use the equation Fg=G(m1m2 / r2).

r is the distance between the centers of the two objects.
G is the gravitational constant (so I just leave that as G, right?)

But, is the sun or the earth m1?

2. Oct 14, 2007

### Ecterine

Wait... I just realized how stupid of a question that is. Why do I do this when I'm so tired?

3. Oct 14, 2007

### Ecterine

K, so now for a better question!

Fg=G(5.98x10^24kg x 1.99x10^30kg / 150,000,000 km)
Fg=G(7.933 x 10^46)

Am I on the right track? What do I do with the G?

I know that the gravitational constant G has a value G=6.67x10^-11 N x m2/kg2

If I plug the mass of the sun in as m2 it is...

G=6.67x10^-11 N x 1.99x10^30kg/kg2

but... now I'm lost. :(

4. Oct 14, 2007

### Ecterine

Fg=(6.67x10^-11 N x 1.99x10^30kg / kg2) (7.933 x 10^46)

:(

5. Oct 14, 2007

### thiotimoline

The formula for gravitation is F=GMm/R^2. Some people may prefer to rewrite it as F=GM1M2/R^2. Just need to take note that M1 or M is the primary mass and M2 or m is the secondary mass. In this question, the mass of Sun is taken to be M1 or M.

Data used:
Gravitational constant = 6.67x 10^-11 Nm^2kg^-2 = G
Mass of Sun = 1.99x 10^30 kg = M
Mass of Earth = 6.02x 10^24kg = m
Distance between Sun and Earth = 1.5x 10^11m = R

Force acting on Earth by Sun = GMm/R^2
= 3.39X 10^22 N

6. Oct 14, 2007

### Ecterine

Thank you! :)

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