# Confused about forumla

F = Gmm'/r^2

Does this explain the sum or total gravitational force between two bodies?

## Answers and Replies

rock.freak667
Homework Helper
F = Gmm'/r^2

Does this explain the sum or total gravitational force between two bodies?

It's just the gravitational force between two point masses. The gravitational force is equal and opposite on each mass.

If you have three masses, you'd need to apply more rules with the formula to get the resultant force.

Ok thank you.
Maybe you can help with this question as well...

During a jump off a diving board, is your apparent
weight (a) equal to your true weight, (b) slightly less
than your true weight, (c) slightly more than your true
weight, or (d) zero?

The answer is zero? I thought it would have been (b)

Last question... what is the equation...

F is proportional to m/r^2

Actually one last question also... Why do we use the gravitational constant G?
Is this only relevant to earth? therefore if I wanted to calculate the gravitational force of an object to mercury I would have to use another value that is not G?

DaveC426913
Gold Member
Ok thank you.
Maybe you can help with this question as well...

During a jump off a diving board, is your apparent
weight (a) equal to your true weight, (b) slightly less
than your true weight, (c) slightly more than your true
weight, or (d) zero?

The answer is zero? I thought it would have been (b)

Why do you think it would have been b?

If you held a bathroom scale against your feet during your jump, what do you think the scale would show as your weight?

rock.freak667
Homework Helper
Actually one last question also... Why do we use the gravitational constant G?
Is this only relevant to earth? therefore if I wanted to calculate the gravitational force of an object to mercury I would have to use another value that is not G?

G is a universal constant, so in any calculation with that formula you'd use one value of G.

Why do you think it would have been b?

If you held a bathroom scale against your feet during your jump, what do you think the scale would show as your weight?

Zero... but that's because you don't have the natural force of the ground to push up on the scale, which in return determines the weight....

But I also know w = mg.... and you have to have some initial acceleration greater than g and NOT zero to move upward... there for weight would exist..... would it not?

So if I was listening to my self I should have actually said the weight would stay the same.

DaveC426913
Gold Member
So if I was listening to my self I should have actually said the weight would stay the same.
Weight is what a scale measures. It measures the force placed upon it. On the moon you would weigh less.

How much would you weigh in space, if you pressed the scale against your feet? (What would keep the scale pressed against your feet if you let go of it?)

How much would you weigh if you pressed it against your feet while suspended in midair (after you've left the ground)?