Can torque be fully understood through classical mechanics alone?

[Studiot]

Actually you didn't mention energy or work once.

The force W moves down a distance equal to L₂.

Thus work done = force times distance = WL₂

This equals the loss of potential energy of the plank.

This can be equated to the kinetic energy of the plank.

If you like you can develop a more complicated equation connecting the conversion of potential energy to KE by the motion of the plank.
However we all know that this is just the motion of a pendulum of weight W suspended from a light rod or string of length L₂.

In the absence of friction or other restraining force this interchange will go on forever as the plank swings upward past vertical to the horizontal the other way and so on.

 

[aaaa202]

hmm yes, I could've done that, but all of this is really trivial and not what I want to understand.

So let's for the last time try to consider when F=W.
The Center of Mass is in equilibrium until the hinge pushes down on the rod. In order for it to do that the torque somehow has to make the rod push against the upper end.
But in my universe a torque can't do that, because a torque is only something that works, when an object is in motion.

But my understanding of torque is wrong, and I think I'll read up on some other books, that present the subject more clear. I've asked my instructors and teachers, and they were not able to answer my question, unless you took some empirical knowledge for granted.

 

[Studiot]

You have been told several times by several responders that the case of F=W is not an equilibrium case as you have presented it.

If you worked through my cases, rather than dismissimg my comments as trivial, until you reached this one you would prove that.

You need to try to appreciate the universe as it is not as you would like it to be to fit your own theories.
That approach will become increasingly counterproductive as your studies progress.

 

[aaaa202]

I perfectly understand it's not an equilibrium. Did I say otherwise?

The sum of torques is non-zero making the pivot exert a downwards force. I'll try to read through them again, but really I got nothing than that from the posts.

But equilibrium is just a word. If I push on the end of a wrench it will translate and rotate. I just don't understand what initiates rotation.

I do NOT make my own theories. I always accept how the equations look, but that shouldn't prevent me from trying to understand them through familiar concepts.

If the notion of an equilibrium lies in the way I present the case, can you try to present it step for step the way you would.

The one thing I learned was the remark about signal propagating through objects at the speed of sound.

 

[Studiot]

Some of this is very basic stuff and has also been mentioned indirectly by others.

If you have a pair of masses there is a gravitational force between them. No energy is required to initiate or maintain this force.

You can say the same about the reaction forces between your table and the glass of beer on it.
However these forces only appear as needed, unlike gravity, which no one except scifi authors has ever got away from.

Energy (only) becomes involved when something changes and work is done.

Rotational effects are similar.
Torque or moment may always be present in a system or appear as a reaction when necessary.

No energy is required for this.
Energy does become involved when something changes rotationally.

 

[aaaa202]

Well then we agree, and I just need to accept torque through more than just an energy consideration.

Anyways, thanks for all the help, though I think we kinda talked in our own directions at some points. Exam is tomorrow..

 

[Studiot]

Exam is tomorrow

sleep well then and good luck.