Understanding the Direction of Lorentz Force: Equation vs. Rules

[Ferruccio]

Lorentz force is explained or demonstrated using Fleming's Left Hand Rule or the Force equation using cross product.
What I'm trying to ask here is, why is the direction fixed using the Left Hand Rule or the equation? Why is the direction here and not there?

Equation and rules are the easiest way to explain the force direction, but they don't explain why.

 

[Vanadium 50]

I have never heard of the left hand rule, but if you are asking why this has the handedness it does, it's all a matter of how we define the direction of the magnetic field.

 

[Ferruccio]

Nope, I'm not asking about the determination of direction. I'm asking about why the direction.

Let me rephrase my question, let's say my current, I as my a_y, magnetic field, B as my a_z, why is the force, F as a_x? why not F = -a_x or some other directions?

 

[Vanadium 50]

why is the force, F as a_x? why not F = -a_x

That's what's measured.

 

[Ferruccio]

Is there a reason for it, a theory behind, or it is a natural phenomenon which is inexplicable?

A reason for it as in, we can hear sound using ears, because the sound is in human audible range. It's a natural phenomenon too, but a reason to explain why.

 

[Nabeshin]

You're creating an effect where there is none. Let's say we cross ay and az and get -ax. Instead of wondering "oh why the negative sign?" we say "we like positive things, so let's switch the direction of the x-axis!" So now ay cross az is ax.

That's all the handedness convention is, we're choosing our axes such that this works out. Nothing mysterious or physical about it. Just choosing coordinates.

 

[Bob S]

Read https://www.physicsforums.com/showthread.php?t=251261

Bob S