# Gravitational Field Strength due to a Uniform Rod

1. ### Quarlep

257
I am trying to learn Physics an dI am reading a booK about classical mechanics.I a stuck somewhere in there If you know a gravitational force to a uniform rod I saw there a x and dx Why we need them ?

Thanks!

2. ### mathman

6,566
You need to integrate the gravitational effects of infinitesimal lengths along the rod to get the total for the rod.

### Staff: Mentor

That's part of the notation of calculus. If you'd tell us what the book was, we'd be certain... But chances are that they're dividing the rod into slices and using dx as the thickness of each slice and x as the position of the slice along the rod. Then the contribution of each slice can be approximated from Newton's inverse-square law and calculus provides the mathematical tools to add all the contributions up as the number of slices approaches infinity and the thickness of each slice approaches zero - and a proof that this process yields an exact answer.