# Need help with Coulomb's Law

1. Feb 6, 2012

### Phy726

1. The problem statement, all variables and given/known data
How does …
(a) the electrostatic force exerted by a proton on an electron compare to the electrostatic force exerted by an electron on a proton?
(b) the gravitational force exerted by a proton on an electron compare to the gravitational force exerted by an electron on a proton?

2. Relevant equations
F = kq1q2 / r2

3. The attempt at a solution
Will the opposites attract when their is electrostatic force?
And repel when there is a gravitational force

2. Feb 6, 2012

### DrewD

Newton's 3rd Law is all you need.

Gravity acts on Mass, not electric charge.

3. Feb 6, 2012

### Phy726

How would the electrostatic force compare from a proton on a electron to vice- versa?

4. Feb 6, 2012

### Phy726

Does the electrostatic force stay the same because the charge of the proton and electron are the same as well as the coulomb constant and radius?

5. Feb 6, 2012

### DrewD

$F=\frac{q_1q_2}{4\pi\epsilon_0r^2}$ is the magnitude of the force. Will that change?
$q_1q_2=q_2q_1$ since they are scalars. But you don't even need that equation to answer the question (your teacher might want you to compute it anyway, but it is unnecessary to answer the question). The answer comes from Newton's third law.

6. Feb 6, 2012

### DrewD

Yes. Those are the same. All that changes is which particle is being acted upon.