# Electric Charge/Gravitational Pull

1. Jan 12, 2014

### KTiaam

1. The problem statement, all variables and given/known data
So in class we are learning about electric charge and we were shown a video of a small ball being attracted to a larger ball by an electric charge. We are given some data about the balls below. There are two questions associated with this problem.

(we are trying to prove that the force shown from the video was to large to be a graviational pull, and thus it is a electrical force)
1.
Calculate the attractive gravitational force that the spheres exert on one another.
2.
Calculate the actual force that is being exerted on the small ball by the large ball to pull it away from vertical by the angle shown in the diagram.
(diagram is just a small ball on rope being attracted to a bigger ball)

2. Relevant equations
Mass of Big ball = 150g
Radius of Big ball = 10.0cm

Mass of Small ball = 0.05 g
Radius of Small ball = 0.5cm

3. The attempt at a solution

I know how to do the first problem, what im having problem is understanding the second problem. There is no force besides electronic force acting on it, correct? What equation do i use.

any help is greatly appreciated.

2. Jan 12, 2014

### haruspex

If that were the only force the small ball would accelerate until it hit the larger ball. What stops it?
(Btw, it's an electric force, not an electronic one.)

3. Jan 12, 2014

### KTiaam

tension due to the string?

4. Jan 12, 2014

### haruspex

Yes, and there's a third force. Draw the free body diagram, with the ball pulled a little towards the larger ball by the electric field, so that the string is not vertical. What equations can you write down?

5. Jan 13, 2014

### KTiaam

tension and gravity

6. Jan 13, 2014

### haruspex

So you have the three forces. What about the equations (∑F=0)?