# Homework Help: Gravity and Phyics

1. Feb 6, 2005

### ChrisP2006

I really really need help with his..

How can I make a formula that will give me the force of gravity at different elevations? Like.. x would be elevation and the y would be the force of gravity. I know I have to use Newton's law of Univerisal gravitation and sutff, but I dont know where to go. Thanks..

2. Feb 6, 2005

### Curious3141

Give the expression for Newton's law of gravitation. Remember that the gravitational force can be taken to act from the center of mass of the Earth, which can be presumed to be the center of an (assumed) spherical Earth. The total distance between a point mass at an elevation x and the center of the Earth is $$x + R$$, where R is the radius of the Earth.

3. Feb 7, 2005

### ChrisP2006

Hm..

I am still very confused. When using the Universal Law.. I understand that Fg in the law is what I need to find.. and I also understand that if you graph what I'm looking for, you would get an inverse.. But after that.. I'm really lost.

would it be something like: y = G * 1/(r+x)^2 ?

r being the radius of the earth, G being the constant, x being the elevation, and y being the force of gravity???

Last edited: Feb 7, 2005
4. Feb 7, 2005

### WORLD-HEN

According to classical theory, the force of gravity would be
$$\frac{G m_1 m_2} {R^2}$$

R being the distance from the centre of gravity. Since you want to find the force of gravity on a body elevated from the surface of the earth by $$h$$ ,assuming the earth is spherical, the total distance from the centre of gravity is $$r + h$$, where r is the radius of the earth. I'll leave the rest to you.

Last edited: Feb 7, 2005