## coolsday one year ago What is the similarties and differences among electrostatics, gravitational and magnetic forces?

1. theEric

I'm a little busy, but I'll give you suggestions. Look at the form of their equations. Think; is does this force depend on some sort of polarity?

2. coolsday

what do you mean by polarity?

3. coolsday

and is the magnetic force equation F=BILsintheta?

4. theEric

I mean things like like charges repel, opposite charges... like poles repel, opposite poles... matter.... err.... uhh... yeah. That sort of thing!

5. theEric

There are lots of equations for magnetic force! It depends on what you look at the magnetic force of! Most importantly, does it look like the equations for electrostatic and gravitational forces?

6. coolsday

no it dosent

7. coolsday

Hey, can you help me with a question?

8. theEric

Right! :) How do the electrostatic and gravitational forces compare to each other though? :) Maybe... I'm getting distracted from my own homework, but I should focus... It doesn't hurt to post it anyway!

9. coolsday

the electrostatic forces and gravitational forces are similar in equation except for their constants. They increase with a direct proportion of their masses and decrease inversely with the distance squared. However, electrostatic forces can attract and repel while gravitational forces can only attract. Is there anything else?

10. theEric

I think that's great! I would specify "direct proportion of $$\sf the\ product\ of$$ their masses," just to be picky.

11. coolsday

how about "forces vary directly with the product of the charges/masses"?

12. theEric

Right! Throw in that distinction between gravitational and electrostatic.

13. theEric

Maybe say "decrease directly" or something.. What wording is proper confuses me sometimes. You could get away with directly proportional to the product of masses for gravitational and charges for electrostatic and inversely proportional to the square of the length of separation or something like that.

14. coolsday

ok thanks. Can you help me with another one? A horizontal 6 m long wire that runs from west to east is in a 0.03 T magnetic field with a direction that is northeast. If a 4.5 A current flows east through the conductor, then what is the magnitude and direction of the force on the wire? I found the magnitude to be 0.5 N but how would i find the direction of the force?

15. theEric

I'll just trust your magnitude, because I forget the equation for current. I think you posted it above, though. Anyway.... The right hand rule! Take your right hand, fingers outstretched. Point it in the direction of the current. Now curl your fingers so that they align with the magnetic field, but don't move your palm. Stick your thumb out. Your thumb points to the direction of the force.

16. theEric

Actually, opposite. That is because of the cross product. $$\vec x\times\vec y=\vec z$$ in our coordinate system, so I remember that. For the magnetic force on a moving charge, its $$q\vec v\times\vec B=\vec F$$ where $$\vec v$$ is the velocity and $$\vec B$$ is the magnetic field.

17. theEric

Wait, not opposite, I was right, I think :)

18. theEric

I'm pretty sure I'm right :) All but positive.

19. theEric

99% Just tired :P

20. coolsday

would the magnetic field be like this |dw:1398305079394:dw|

21. theEric

Yep. If north is up and east is right, you're correct.

22. theEric

So the current would be to the right.

23. theEric

The current, when considered "conventional current," is the flow of positive charge.

24. coolsday

ok, so the force would be perpendicular to both the current and magnetic field?

25. theEric

Right.

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