# Homework Help: Force on a charged object

1. Jun 17, 2007

### streetmeat

If a charged object experiences say, an attractive force, as it moves closer to the other charged object doesn't the force increase.. so how can you ever have uniform acceleration with moving charged objects? can't it only be instantaneous acceleration? how can you apply the kinematics equations then?

2. Jun 17, 2007

### streetmeat

Another question..

if one positively charged sphere Q, of mass m is held by a string attached to a vertical pole, and one negatively charged sphere is held at a distance, r, away from the sphere, how do i find the angle between the string and the vertical pole? i know to use coloumbs law to find the force between the 2 spheres.. but that's about it. they don't even say the length of the string or the pole

3. Jun 18, 2007

### olgranpappy

Yes.

Well, as you stated above, you should find a situation in which the distance between the objects remains constant. It is often useful in this situation to contemplate the moon... In analogy with gravity, not werewolves.

4. Jun 18, 2007

### arunbg

Apart from centripetal acceleration, constant linear acceleration of charges is also possible.
There are many ways by which a uniform electric field can be created, such as by using a very large conducting planar sheet of charge. In these cases the electric field is invariant of distance, and hence acceleration remains constant.

For the second question, draw the free body diagram of the suspended charged sphere and try to balance all the forces, so that the sphere is in static equilibrium.

5. Jun 18, 2007

### Staff: Mentor

This sounds like a homework or coursework question. streetmeat, welcome to the PF. Homework and coursework questions need to be posted in the Homework Help forums, and not here in the general forums. I'll move this thread over to the HH forums now.