# Force between two charged bodies!

## Homework Statement

Suppose I had a large sphere with 10 protons and 10 neutrons. Another sphere with 2 protons and 2 electrons. How many different electrostatic forces would be acting between the two spheres? What would be the likely net force between the two spheres in this example? How would this change if I stripped 2 electrons away from the larger sphere?

## Homework Equations

Coulomb's law

F=k(q1^2)(q2^2)/d^2

## The Attempt at a Solution

what do they mean by how many "different electrostatic forces"?
Would the net force be 0? and i don't think it would change even if i stripped away 2 electrons?

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cepheid
Staff Emeritus
Gold Member
What is q1 (the charge on the first sphere)? What is q2 (the charge on the second sphere). Plugging these into coulomb's law will give you the total (net) force between the spheres.

Each sphere has a number of electric charges on it, and each charge on the first sphere interacts with every charge on the second sphere. Of course, the sum of these interactions should just be the same as the total one you calculated using the above method (by just looking at overall charge totals).

wait... is the charge 10 and 2 respectively?
also, what do they mean by how many different electrostatic forces?

cepheid
Staff Emeritus
Gold Member
wait... is the charge 10 and 2 respectively?
Well, what is the charge of a proton? How about a neutron? And an electron? Add them up for each sphere.

also, what do they mean by how many different electrostatic forces?
I had intended this statement below as an answer to that question. Sorry if I wasn't clear.

Each sphere has a number of electric charges on it, and each charge on the first sphere interacts with every charge on the second sphere.

if you add them up.. it's 0.

....the electrostatic charge is just neutral because of the protons and electrons...

cepheid
Staff Emeritus
Gold Member
Yes. The net charge of two protons and two electrons is zero. So q2 is zero. So sphere 2 is uncharged and feels no force from sphere 1.

so there are no electrostatic forces.
but the net force would be more positive if you did strip 2 electrons away from the larger sphere. is there a specific number for the "net force". would it be.. 6?

cepheid
Staff Emeritus
Gold Member
so there are no electrostatic forces.
There is no NET electrostatic force, but there are individual electrostatic forces amongst the various individual charged particles that are present. Like I said twice before, every individual charged particle on the first sphere exerts a force on every individual charged particle on the second one. It's just that all of these forces add up to zero. The question still wants you to count how many of them there are.

but the net force would be more positive if you did strip 2 electrons away from the larger sphere. is there a specific number for the "net force". would it be.. 6?
Even if you stripped two electrons away from the *larger* sphere (the one with the 10 protons and 10 neutrons), making its net charge more positive, the smaller sphere would still be neutral, and there would still be no force acting.

I don't understand the rest of your question. What does, 'is there a specific number for the 'net force'" mean?

i was wondering if the net force would change though.
because it wouldn't be 0, would it? or it would stay 0 because the smaller sphere is 0?