Why does torque point in Right Hand rule direction?

Question

Ever since I took basic physics and learned about the Right Hand rule for Torque, I could never figure out why would this rule is the way it is. I mean, if you are facing a wheel and turn it counter-clockwise, why does it always direct (point) towards but not away? I would really love to read about why this is, because I've researched briefly on some search engines and most of them just explained torque as change in direction and its equation formulas. So far, it just seemed like the creater for the law of physics for this universe just "picked" a direction to point when you rotate things...

Answer 1

Torque is defined as the cross product of position vector (to the point of application) and the applied force.

It is the rate of change of the angular momentum, which is the cross product of position vector and the linear momentum.

What is absolute about this definition is the axis of the direction: perpendicular to the plane containing the force and the position vector. However, whether you use the "right-hand rule" or a "left-hand rule" is a matter of convention. Once you make that decision for angular momentum, you have to keep to the same convention for torque. It doesn't matter which one was chosen, but you have to chose one and stick to it.

Analogies:
- Why do we drive on the right-hand side of the road? Because we needed to chose a convention, and in most of the world, that was the convention chosen.

- Why do electrons have "negative" charge, and protons have "positive" charge? Because they happened to chose that convention. All that is absolute is that electrons and protons must have opposite charge. But if someone had started out with a different convention in the 1800's, we would be using that, and it wouldn't really change our understanding of the physics at all.

Answer 2

Torque Right Hand Rule

Answer 3

It is really difficult to explain this without a diagram, but I will give it a try.

Do you know Newton's 3 Laws?
Even if you don't it doesn't matter that much. Although most of my deductions are based on those.

Let's say, to keep it simple. There is a change in velocity when a force is applied. But if we consider a moment/ circular motion where the linear speed does not change, the only thing that can change is direction. You can try drawing, the only force that can produce a change in direction but no change in linear speed is a force perpendicular to the direction of motion.

That's the first part.
Next, you need to consider an example.

Consider a stone attached to a string been swung in a circular motion - i.e. a horizontal circle.

This must mean that since it is moving in a circle, there needs to be a force acting perpendicular to the direction of motion(which at all times is the tangent of the circular path). Since force can only act where there is matter, and since air can only exert a very little resistance/force the only thing that can sustain the force will be the string to which the stone is attached.

Next part. Imagine the string being cut. What will happen at that instant? Ans: the stone will move in the direction along the tangent. So, until now, it was the string which was supporting the stone.

So, the tension in the wire was pointing away from the stone, towards the centre, trying to keep the stone near.

Last thing to clarify for you, the centripetal force is not a force in itself. In fact, the centripetal force is the sum of the forces which act so as to maintain circular motion. So, here, in this example, the centripetal force was the tension in the string.

That's as much as I can do. If you need any clarification, you can ask.

One thing I really did forget. Torque, in physics, has no direction. In fact it is just a scalar quantity. So that's why you got nothing but equations about Torque. What you needed to search was about circular motion.

Answer 4

Right Hand Rule Torque

Answer 5

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Answer 6

The torque vector points in that direction, only because of convention, and not because of a deep physical reality. So you are right: someone had to "pick" a direction. The only important thing is to apply the rule consistently.

For example, circularly polarized EM waves had a different vector convention in Europe and in the U.S., which led to confusion in an early communication test.

Answer 7

The RHR exists by definition, by convention. Do you want to hear a really bizarre convention...current flows from plus to minus in an electrical circuit. Thus + -----------> - is the convention for a current's direction.

That's the convention for hundreds of thousand electricians in the world. Yet, we physicists know darn well that electrons flow from minus towards the plus. As a student, when I took both EE and physics courses, that used to drive me nuts.

No, there was no "creator" who picked the direction of torque. It was likely some early on alchemist, aspiring to be a physicist, who made that choice.

Answer 8

It is a convention based on the definition of torque as the cross product R X F and the definition of the cross product X. Torque could just as easily been defined as F X R, which is in the opposite direction. I suggest sitting down and puzzling over the definition of cross product in 3-D Cartesian coordinates.

Answer 9

not sure