## ← 08-08 Charge vs. Mass

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Showing Revision 1 created 07/31/2012 by Amara Bot.

1. It's not like there are some real similarities between charge and mass.
2. Specifically, similarities between the electric force and the gravitational.
3. Let's do some comparison to see just how similar or how different these forces are.
4. First, let's analyze the cause of each force.
5. Well, the electric force is caused by charged objects
6. whereas the gravitational force well it's caused by massive objects.
7. Charge and mass are the causes of these forces.
8. What about the effect? What kind of object feels the effect of the electric force?
9. Well once again it's an object with a charge.
10. Likewise, gravitational force is felt by objects with mass.
11. Notice that we already see one similarity.
12. The thing that causes the force is the same as the thing that feels it. What about the force law?
13. And by force law I mean what's the equation that describes these forces?
14. Well with gravity we knew the force of gravity was proportional to 1
15. over your distance away from the mass of object that's causing the force.
16. In the case of the earth and the moon, r would be the separation between the two bodies.
17. With the electrical force, it turns out the force law is almost identical.
18. It's still proportional to 1 over r². So doubling the distance will decrease the force by a factor of 4.
19. What about the direction of force? Well for gravity, objects always attract each other.
20. In fact, it's this attraction that allows large bodies like the earth to form
21. because every little tiny chunk of rock is attracted to every other little tiny
22. chunk of rock and together they coalesce and form this wonderful beautiful sphere.
23. What about with electricity? This is where things get interesting.
24. With electricity, the direction is not always attractive. Sometimes it's repulsive.
25. And this one key difference is responsively for many of the fascinating
26. aspects of electricity which well we can learn about now.