# Need help coming up with dl in cylindrical coords.

vwishndaetr

The whole problem consists of several parts, but my issue is to come up with a dl for the peice of wire shown.

Im trying to find the force on the wire due to a magnetic field produced by another wire running along the x-axis (not shown in pic).

$$\vect{B} = \frac{\mu_0I}{2\pi s}\hat{\phi}$$

I am trying to get my dl x B so I can integrate, but I cannot come up with a dl. The reason I'm having trouble is because I know in cylindrical, for dl, both phi hat and s hat change along integration path for dl.