Calculating Force of Gravity at Different Elevations with a Robot

[Zerd_2011]

I am working on a formula to help me calculate the force of gravity at different elevations on a robot as it climbs up a skyscraper. The robot is attached to four magnetic wheels (each with a pull force of 4 lbs) which attaches to the steel framer.

In order to find the g's on the robot, i have used three different formulas:
(g+r)/g
(torque)=Fr
F=ma

and i have come with this equation to find the number of g's on the robot:

g's= ((torque) + gmr)/(gmr) using those three formulas

Now that i have figured out the value of g, how do i find the force at different elevations?
How do i use the gravitational law with the formula i already have?

Am i going about this all wrong? Any input would be appreciated.

 

[mathman]

Gravity at the Earth's surface is 9.8 meters/sec². In general, it is proportional to r², where r is the distance to the center of the earth. If you want to be VERY precise, you need to multiply by (R/(R+h))², where R is the radius of the Earth and h is the height of the elevator. Unless h gets very big, the adjustment is probably unnecessary.

 

[spancho]

Im going to assume that you know how tiny the difference in weight is going to be from the top of the building to the bottom. The best way to calculate the force of gravity is to use Newtons approximation G*(g1*g2)/r^2.

It looks like your also calculating the centrifugal force due to the object rotating around the Earths axis. Although this will effect the net force on the object it has no bearing on the force of gravity.

 

[tatiana]

For torque you also need to consider once you draw out a picture, teh equationg T=mgx x being teh centrial mass and mg ofcouurse mass times gravity or even T=r(Fsin theta)