Torque question

[Relative]

In a reference frame of an object been rotated from a central point on a bar in a circular motion, is the torque directed along the bar centrifugally with no centripetal force acting on the bar?

Edited October 5, 2014 by Relative

[studiot]

You need to understand what 'torque' is before you can understand the answer.

 

The answer is that the torque vector is directed at right angles to the plane of motion so it it lies in none of the directions you mention, which are all in the plane of motion.

[Relative]

You need to understand what 'torque' is before you can understand the answer.

 

The answer is that the torque vector is directed at right angles to the plane of motion so it it lies in none of the directions you mention, which are all in the plane of motion.

I am sorry I do not understand what you have put,

 

 

Is torque not in the direction of this diagram in this process?

 

If not , could you possibly edit my diagram and put in the torque tag?

[studiot]

 

If not , could you possibly edit my diagram and put in the torque tag?

 

 

Not really.

 

Torque is a three dimensional effect.

 

Please ask what you really want to know about masses in circular motion.

[physica]

also there is no force pulling the block outwards. Centrifugal force doesn't exist. Google it if you don't believe me

[Relative]

also there is no force pulling the block outwards. Centrifugal force doesn't exist. Google it if you don't believe me

My apologies , the pivot point is motorized if that helps. So what direction is the torque centrifugal?

[John Cuthber]

It might clarify things to point out that the torque that spins a wheel is a vector along the axle.

This might also help

http://en.wikipedia.org/wiki/Torque

[andrewcellini]

relative it might help to draw a free body diagram of the forces to find out if there is a torque.

however looking at your diagram i'm not sure what is supposed to be happening.

Edited October 5, 2014 by andrewcellini

[Strange]

however looking at your diagram i'm not sure what is supposed to be happening.

 

It took me a while to work it out! The ellipse marked pivot is the axle; the rectangle is rotating around it; the big arrow is the centrifugal force (arguably pointing in the wrong direction).

 

So, Relative, the convention for torque is that it points into (or out of) the plane of your diagram. There is an animated diagram on the Wikipedia page.

[Relative]

 

It took me a while to work it out! The ellipse marked pivot is the axle; the rectangle is rotating around it; the big arrow is the centrifugal force (arguably pointing in the wrong direction).

 

So, Relative, the convention for torque is that it points into (or out of) the plane of your diagram. There is an animated diagram on the Wikipedia page.

Thank you , and yes arguably about direction, so if i changed the bar that holds the rectangle to an elastic band, what torque if any is inwards?

Edited October 5, 2014 by Relative

[Fuzzwood]

None since you are misunderstanding torgue.

[Relative]

None since you are misunderstanding torgue.

Yes i think i am misunderstanding torque, and I have used a torque wrench at that,

[studiot]

 

Yes i think i am misunderstanding torque, and I have used a torque wrench at that,

 

 

Rest assured, many misunderstand torque.

 

I am not even sure if torque is the appropriate quantity for what you want, which is why I asked

 

 

Please ask what you really want to know about masses in circular motion.

 

 

Just ask your question in ordinary words and don't try to use technical terms.

 

Allow others to introduce and explain technical terms and see how they use them.

And, of course, ask for an explanation if they use a term you don't know.

But don't guess.

[Relative]

 

Rest assured, many misunderstand torque.

 

I am not even sure if torque is the appropriate quantity for what you want, which is why I asked

 

 

Just ask your question in ordinary words and don't try to use technical terms.

 

Allow others to introduce and explain technical terms and see how they use them.

And, of course, ask for an explanation if they use a term you don't know.

But don't guess.

Ok thank you , can someone please explain in simple terms the meaning of torque?, I looked on wiki and the diagram lost me.

i thought it was the force to move something?

When a torque wrench reaches its equal force strength it slips its clutch?

Edited October 5, 2014 by Relative

[Bignose]

Ok thank you , can someone please explain in simple terms the meaning of torque?

Go grab a ruler and put it on a smooth surface. (Let's assume it is a meter stick.)

 

Poke the ruler right on its midpoint a few times (if this is the assumed meter stick, this is right on the 50 cm mark).

 

Note how when you poke the ruler on the midpoint, the whole rule slides away from you.

 

Now, poke the ruler out on an end (again, if it is a meter stick, at the 20 cm mark or the 80 cm mark works well).

 

Note how when you poke the ruler someplace that is not the midpoint, the rule rwill rotate.

 

This is an example of torque. When you apply a force on an object that is not on that object's center of mass, this rotational force is called a torque.

 

When you poked the center of the ruler, you poked its center of mass, hence no rotation. When you poked out near the end of the ruler, that was not the center of mass, hence you caused some amount of rotation about the center of mass.

 

Further note that the same poke a small distance from the center of mass causes less rotation than the same poke near the end. The amount of rotation is a function of how far away from the center of mass the force of rotation (or torque) is applied. Another example of this is how much easier it is to open a door by pushing on the handle far away from the hinges, vs. the middle of the door, or right next to the hinges.

 

Once you have that down, we can talk about the notation convention for how torque is drawn on a free body diagram.

Edited October 6, 2014 by Bignose

[Relative]

Go grab a ruler and put it on a smooth surface. (Let's assume it is a meter stick.)

 

Poke the ruler right on its midpoint a few times (if this is the assumed meter stick, this is right on the 50 cm mark).

 

Note how when you poke the ruler on the midpoint, the whole rule slides away from you.

 

Now, poke the ruler out on an end (again, if it is a meter stick, at the 20 cm mark or the 80 cm mark works well).

 

Note how when you poke the ruler someplace that is not the midpoint, the rule rwill rotate.

 

This is an example of torque. When you apply a force on an object that is not on that object's center of mass, this rotational force is called a torque.

 

When you poked the center of the ruler, you poked its center of mass, hence no rotation. When you poked out near the end of the ruler, that was not the center of mass, hence you caused some amount of rotation about the center of mass.

 

Further note that the same poke a small distance from the center of mass causes less rotation than the same poke near the end. The amount of rotation is a function of how far away from the center of mass the force of rotation (or torque) is applied. Another example of this is how much easier it is to open a door by pushing on the handle far away from the hinges, vs. the middle of the door, or right next to the hinges.

 

Once you have that down, we can talk about the notation convention for how torque is drawn on a free body diagram.

You should write Wiki, Thank you that was very simple to understand, So torque is force that is not applied to the center of a mass, forcing angular momentum?

If my tracking is not aligned correctly on a car, the torque will try to force my steering in the direction it is off?

Edited October 6, 2014 by Relative

[swansont]

You should write Wiki, Thank you that was very simple to understand, So torque is force that is not applied to the center of a mass, forcing angular momentum?

 

 

Torque is not a force, though it is analogous to force for rotation. If you try and equate it with force, you will likely end up with a very confused mess.

 

Torque occurs when a force is applied away from the center of rotation, and changes the angular momentum, much like a force will change linear momentum.

 

T = r x F (these are vectors, and that is a cross product)

 

So T = rF sin(theta). You need a force, a separation distance from the rotation point, and the force directed toward or away from the rotation point will not contribute; only the perpendicular component will have an effect.

[studiot]

 

So torque is force

 

No, No, a thousand times No.

 

Torque is not a force.

 

Torque is an entirely separate effect.

 

Mostly it is the result of a force, but there are other agents that can apply torque as in a Wankel engine.

 

When considered in conjunction with a force, torque is the product of the magnitude of that force and a distance, called the lever arm.

 

This is more difficult than and often confused with work = Force x Distance.

 

A simple way to distinguish is that no (zero) work is done at distances measured at right angles to the line of action of the force.

Work is force times distance measured in the direction of that line of action.

(You have discussed this in other threads)

 

Torque, on the other hand, is Force times distance measured at right angles to the line of action.

We know (I have just said) this the work calculated this way is zero so torque is not work either.

 

That is enough for now.

[Relative]

 

No, No, a thousand times No.

 

Torque is not a force.

 

Torque is an entirely separate effect.

 

Mostly it is the result of a force, but there are other agents that can apply torque as in a Wankel engine.

 

When considered in conjunction with a force, torque is the product of the magnitude of that force and a distance, called the lever arm.

 

This is more difficult than and often confused with work = Force x Distance.

 

A simple way to distinguish is that no (zero) work is done at distances measured at right angles to the line of action of the force.

Work is force times distance measured in the direction of that line of action.

(You have discussed this in other threads)

 

Torque, on the other hand, is Force times distance measured at right angles to the line of action.

We know (I have just said) this the work calculated this way is zero so torque is not work either.

 

That is enough for now.

I understand the lever arm bit, can you explain Torque using a Fulcrum, ?

[studiot]

 

I understand the lever arm bit, can you explain Torque using a Fulcrum, ?

 

Please don't try to pre-emp what I am going to say.

 

It would be really helpful if you would indicate what continent your are on because the definition of Torque depends upon where and when you are.

 

This is because American authors in the later part of the 20th century started using torque to mean what every one else had always called 'moment' (since before there was an America).

 

So I will try to tailor my response to the information you might meet. It can be very confusing when different folks call something by different names.

Edited October 7, 2014 by studiot

[Relative]

Please don't try to pre-emp what I am going to say.

 

It would be really helpful if you would indicate what continent your are on because the definition of Torque depends upon where and when you are.

 

This is because American authors in the later part of the 20th century started using torque to mean what every one else had always called 'moment' (since before there was an America).

 

So I will try to tailor my response to the information you might meet. It can be very confusing when different folks call something by different names.

Some people would say I am on cloud 9 lol, but I am in England,

[studiot]

OK, there are several turning/twisting effects and torque is one of them.

 

Here is an extract from a thread started by someone with the same questions you have

 

 

1) A single force exerts a moment about any point in the plane containing both the force and the point, which may be zero if the force passes through that point.

The moment is different about any other point in that plane.

 

2) A pair of co-planar equal opposed forces exerts a couple about any point in the same plane.

This couple has the same turning effect about any point in that plane. Compare with (1) above.

 

3) If a moment or couple is acting about some point in a plane, the turning effect can be transferred to another plane parallel to the first along a line at right angles to both planes and passing through that point (called the axis of torsion). This effect is then called 'torque'. A screwdriver is a common example.

 

 

 

There are some useful sketches in post#10 and another simple experiment like Bignose's in post#16.

 

 

http://www.scienceforums.net/topic/80386-is-there-angular-force-tangential-force-why-is-tangential-f-scaled-twice-for-torque/?hl=torsion#entry780312

 

Like subliminal I think you orignally were seeking a quantity called moment of momentum or angular momentum.

 

Structural and mechanical engineers use the terms torsion and torque to distinguish between the turning or twisting along the long axis of a shaft or structural member and the bending moment across the structure.

[Relative]

OK, there are several turning/twisting effects and torque is one of them.

 

Here is an extract from a thread started by someone with the same questions you have

 

 

 

There are some useful sketches in post#10 and another simple experiment like Bignose's in post#16.

 

 

http://www.scienceforums.net/topic/80386-is-there-angular-force-tangential-force-why-is-tangential-f-scaled-twice-for-torque/?hl=torsion#entry780312

 

Like subliminal I think you orignally were seeking a quantity called moment of momentum or angular momentum.

 

Structural and mechanical engineers use the terms torsion and torque to distinguish between the turning or twisting along the long axis of a shaft or structural member and the bending moment across the structure.

Thank you for the thread link, I looked at the diagrams, got a bit lost, but noticed this sentence

 

''This also shows that for true equilibrium a body has be be separately in force equilibrium and in moment equilbrium.''

 

 

What do you mean by this?

[studiot]

The statement is also known as Poinsot's Theorem (1804).

 

Turning effect type 2 in my list - the couple is an example of this.

 

A couple is composed of two equal and opposite parallel forces.

 

Because they are equal and opposite and parallel they balance as forces, but a turning effect is left.

 

If you look at the other thread on difference between a couple and a moment is that the moment of a force is different about every point in the plane, whereas a couple is the same for every point in the plane.

 

Also not that a moment and a couple are 2 dimensional and a torque is 3D in that it transfers the turning effect from one plane to another in 3D.

Edited October 9, 2014 by studiot

[Relative]

The statement is also known as Poinsot's Theorem (1804).

 

Turning effect type 2 in my list - the couple is and example of this.

 

A couple is composed of two equal and opposite parallel forces.

 

Because they are equal and opposite and parallel they balance as forces, but a turning effect is left.

 

If you look at the other thread on difference between a couple and a moment is that the moment of a force is different about every point in the plane, whereas a couple is the same for every point in the plane.

 

Also not that a moment and a couple are 2 dimensional and a torque is 3D in that it transfers the turning effect from one plane to another

So you are telling me that a couple with a net force of zero can rotate anti clockwise , there is angular momentum, and torque exists although a net force of 0?