Question

Hey I have a question.

Answer 1

So, I'm guessing we'll be using \[Fe= k\frac{ q_1 q_2 }{ r^2 }\]

and \[F=G \frac{ m_1m_2 }{ r^2 }\]

But I'm not sure what variable to solve for.

Answer 2

@Kainui @phi

Answer 3

\[Fe=F ?\]

Answer 4

solve for q1 (assume q1=q2)

Answer 5

Ah, ok so I would let Fe = F as I mentioned above right? I thought I was suppose to let the charges equal but wasn't entirely sure.

Answer 6

\[k\frac{ q }{ r^2 } = G\frac{ m_1m_2 }{ r^2 } \implies q = G \frac{ m_1m_2 }{ k }\]

Answer 7

I think they are saying put the same number of electrons on the earth as on the moon
this will create a repulsive force.
and you want this repulsive (electrical) force to balance the attractive gravity force.

Answer 8

it should be q^2

Answer 9

Right, thanks :)!

Answer 10

What a sweet problem to solve.

Answer 11

Haha, I thought so to :)

Answer 12

For some perspective, that's about 500 million moles of electrons placed on the moon.

http://www.wolframalpha.com/input/?i=sqrt%5B%286.67384+%C3%97+10%5E-11%29%285.97219+%C3%97+10%5E24+%29%287.34767309+%C3%97+10%5E22%29%2F%28+8.9875517873681764%C3%9710%5E9%29%5D%2F%5B%281.60217657+%C3%97+10%5E-19%29+*%28+6.02+*10%5E23%29%5D

Answer 13

I'm not sure if I can comprehend that...seems insane.

Answer 14

Well, there are about 10^26 moles of atoms in the entire earth. So it's actually relatively small...

http://www.wolframalpha.com/input/?i=number+of+atoms+on+earth

Answer 15

By an order of magnitude of 10^18 which is a billion billion of a difference. lol

Answer 16

Yes, that's a BILLION of a BILLION

Answer 17

Haha, you're right, also do you see the irony of using wolframalpha to show me such things and I like that Carl Sagan recite.

Answer 18

I got it Isaiah but thanks for sharing :)!

Answer 19

Yeah I think that's part of why I did it, just because of that hahaha

Answer 20

Also, I was curious. A lot of people think gravity is so strong cause it moves the planets, but honestly it's simple to see how weak gravity is.

I can take a balloon, rub a few electrons off with my hair and stick it to a wall

I can take a giant 1,000,000 kg weight and place a feather on a string near it, and you won't even notice the feather being attracted to the mass lol

Answer 21

That's right, also very nice observations, from what I recall gravity is one of the weakest forces surprisingly, from the 4 fundamental forces where its strength is 6*10^-39 or something insane like that where the strong force has a strength of 1.

Answer 22

Gravity is actually the weakest of the four.

Answer 23

Yes, http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html