# Coulomb's law and mechanics

1. Apr 3, 2005

### rindishy123

Hey....i need help....

"One practical arrangement for verifying Coulomb's law is to use a lightweight, negatively charged, freely-suspended ball. it is repelled by the negative charge on a larger sphere that is held near it, on an insulated support. the small angle of deflection, x is then measured.

The weight of the ball is W. show that the force of repulsion F on the suspended ball is given by:

F = W tan x"

I've drawn a free body force diagram, but i still cant work it out..

2. Apr 3, 2005

### Staff: Mentor

Start by identifying the forces acting on the suspended ball. (Hint: Three forces act on that ball.) Then apply the conditions for equilibrium: the sum of the forces must be zero. (Hint: Consider vertical and horizontal components separately.)

3. Apr 3, 2005

### rindishy123

Ok I've got to the point where I've found that the components of N (the normal reaction force) are:

N sin x

and

N cos x

I don't study maths so could you please give me hints as to how I turn the above into F = W tan x???

4. Apr 3, 2005

### Staff: Mentor

I don't know what you mean by the "normal force" in this problem. Answer the questions I asked in my last post: What are the forces acting on the ball?