Physics Right Hand rule: How is the Force acting on line 2 (i2) in the left direction?

Question

two parallel wires going in the same direction.
i1 i2
l l
l l
l l
l l

the magnetic field of i1 is circular (think right hand rule pertaining to a straight wire)

using the other right hand rule (not the one with the circular loop, but the one with the force, magnetic field, and current) how can we determine the direction of the force on i2?

I just can't picture it. I've already tried using the right hand rule, but I'm confused. The only direction I get for the force is up, which is totally wrong.

Answer 1

Point the thumb of your right hand in the direction the current is going through i1. As you curl your fingers, you'll see they must orbit it counterclockwise if the current is running upward, or clockwise if the current is running downward. You can also do this for i2.

Then, compare. Your fingers will point toward the south pole of the magnetic field. If the two currents are running in the opposite direction, then when their magnetic fields "pass" (when the magnetic fields surrounding are closest), your fingers will be pointing in the same direction, thus repulsion (since same poles repel). Likewise, if the two currents are running in the same direction, then when their magnetic fields "pass," your fingers will be pointing in opposite directions, thus attraction (since opposite poles attract).

If it helps, you can even consider your hand as a magnet, with your fingernails as the south poles and your knuckles as the north poles.

Specifically for this case, since the currents are running in the same direction, they are attracted. Thus, as they are attracted, the force on i2 will be to the left (towards i1).

Edit: Rereading your question, we unfortunately don't know the direction of the magnetic field (it is "circling" the current-carrying wire). Thus, we cannot use F=ILxB to determine the force, but hopefully the approach I described above will work for you. Good luck!

Answer 2

it is very true that friction acts against the direction of motion actually there is an extension to this statement that needs to be considered which is more relevant and that is friction acts against the direction of motion or the tendency for motion. the wheel comes into contact with respect to the ground and travels along with it without slip and leaves contact. this means that the case of friction is a case of static friction and not sliding or dynamic friction. thus the friction force is not moving through any distance and consequently does no work. on the other hand this friction is what we call the traction capability because if we apply a greater force at the point of contact than can be supported by this friction force (traction force) the wheel would skid. thus the friction force would be directed in the direction of motion of the bicycle on both the wheels in other words from right to left