A particular magnetic field points west. A proton moved from north to south. What direction is th magnetic force on the proton?

Up,down,east or northwest

right hand rule: http://physicsed.buffalostate.edu/SeatExpts/resource/rhr/rhr.htm RHR1

If I have twisted my arm correctly, it is down.

To determine the direction of the magnetic force on a moving charged particle, you need to use the right-hand rule. Here's how you can apply it to this question:

1. Extend your right hand and stretch your thumb, index finger, and middle finger perpendicular to each other.

2. Align your thumb in the direction of the velocity of the proton (from north to south in this case).

3. Align your index finger in the direction of the magnetic field (west in this case).

4. Your middle finger will then indicate the direction of the magnetic force.

In this scenario, if you align your thumb (southward) with the index finger (westward) using the right-hand rule, your middle finger will point downward, towards the bottom. Therefore, the magnetic force on the proton is in the "down" direction.