- #1

- 99

- 0

Please explain in detail but in simple language pleaseeeeeeeeeeeeee!

You should upgrade or use an alternative browser.

- Thread starter Ali Asadullah
- Start date

- #1

- 99

- 0

Please explain in detail but in simple language pleaseeeeeeeeeeeeee!

- #2

- 648

- 2

The couple has a

On the right: the force F has a

r is the perpendicular distance of the line of action of the force from O.

This is also referred to as the

Torque and moment mean the same thing.

(I have a feeling there may be a slight difference in terminology on different sides of the atlantic on this one. Is this true? Mine is how it is defined in the UK)

- #3

- 99

- 0

Thanks Stonebridge can you please also explain differences in their properties?

- #4

tiny-tim

Science Advisor

Homework Helper

- 25,832

- 251

(I have a feeling there may be a slight difference in terminology on different sides of the atlantic on this one. Is this true? Mine is how it is defined in the UK)

Hi Stonebridge!

I don't think it's a country thing, it's just a general lack of consistency.

"torque" can mean moment

"a torque" can mean a couple

"a pure moment" can mean a couple

… it just depends which book you're reading, or who your professor is

(oh, and I suspect engineers like to talk about applying a torque instead of a couple, as in torque-wrench )

- #5

- 648

- 2

Yes there has always been a bit of inconsistency on this.

I also think this may be what is causing the problem for the original poster.

To Ali

I'm not sure what you are asking for. There isn't really any more to say about these terms. It's easier to talk about actual examples where you have to use them to solve a problem.

Do you have a specific problem we can look at?

- #6

- 5,439

- 9

Firstly there is no ambiguity or inconsistency about these terms. Nor is there any difference bewtween UK and US practice.

All three terms describe a turning effect.

The first two, couples and moments look at things from the viewpoint of the external force needed to generate the turning effect.

A couple requires**two **parallel, equal and opposite forces. It is always a vector (at right angles to the plane of the forces) and has the same effect on any point in its plane. It is non localised.

There is no single force which can be statically equivalent to a couple.

A moment requires**one** force and is localised. A moment about a straight line is a scalar. A moment about a point is a vector.

Edit however that one force can be the resultant of as many as you like acting in combination.

Torque is the actual turning effect itself, regardless of source. It is used for instance to describe the turning effect available at the ouput shaft of a machine - how hard can it turn something? This can obviously be converted to a specific force at a specific distance or a specific pair of forces but there are many solutions.

Torque also appears internally within bodies when we consider**torsion**. It appears in the angular deformation equivalent of Hookes law

Contrast the following for a circular shaft

[tex]\delta = \frac{{FL}}{{AE}}[/tex]

gives the linear deformation, [tex]\delta [/tex], for an applied force F with youngs modulus E, lenght L and cross section area A

[tex]\theta = \frac{{TL}}{{JG}}[/tex]

gives the angular deformation [tex]\theta [/tex], in radians for an applied torque T, moment of inertia, J and shear modulus G.

All three terms describe a turning effect.

The first two, couples and moments look at things from the viewpoint of the external force needed to generate the turning effect.

A couple requires

There is no single force which can be statically equivalent to a couple.

A moment requires

Edit however that one force can be the resultant of as many as you like acting in combination.

Torque is the actual turning effect itself, regardless of source. It is used for instance to describe the turning effect available at the ouput shaft of a machine - how hard can it turn something? This can obviously be converted to a specific force at a specific distance or a specific pair of forces but there are many solutions.

Torque also appears internally within bodies when we consider

Contrast the following for a circular shaft

[tex]\delta = \frac{{FL}}{{AE}}[/tex]

gives the linear deformation, [tex]\delta [/tex], for an applied force F with youngs modulus E, lenght L and cross section area A

[tex]\theta = \frac{{TL}}{{JG}}[/tex]

gives the angular deformation [tex]\theta [/tex], in radians for an applied torque T, moment of inertia, J and shear modulus G.

Last edited:

- #7

tiny-tim

Science Advisor

Homework Helper

- 25,832

- 251

Firstly there is no ambiguity or inconsistency about these terms.

…

Torque is the actual turning effect itself, regardless of source.

Sorry, but I completely disagree.

There

An additional example: torque is perhaps best know in the phrase "torque equals I alpha", where it means the same as "moment (of force)".

(and i suspect that the reason for using the "wrong" word in

- #8

- 648

- 2

I don't think the claim was that theFirstly there is no ambiguity or inconsistency about these terms.

Nor is there any difference bewtween UK and US practice.

I'm glad we all agree on this.

- #9

tiny-tim

Science Advisor

Homework Helper

- 25,832

- 251

I'm glad we all agree on this.

Nooo … I

I particularly like spelling words like "centre" the English way.

- #10

- 5,439

- 9

What fun, I hope you noticed we have a new physical dimension in Somerset after a few ciders

lenght

- #11

- 5,439

- 9

An additional example: torque is perhaps best know in the phrase "torque equals I alpha", where it means the same as "moment (of force)".

Personally I think the best know examples are in either the 'torque wrench' or the output torque v engine speed of say a Ford engine.

Of course torque and moment refer to the same turning effect.

Consider the following.

I have a socket set.

If I attach my 9inch crank bar to the driver I get a certain torque on the nut.

If I attach my 15inch crank bar to the driver I get a different torque on the nut.

Using my torque wrench I can apply only the appropriate torque as specified by the manufacturer.

Again if I now attach and extension shaft between the crank and the socket to reach down into the engine to access a nut, I can define (or measure) the force and the lever arm of the crank to calculate the moment I am applying at my end of the extension.

But what of the socket end? I am applying a torque to the nut but what forces are acting?

Then again If I remove the socket form the nut and rotate it in free air by the crank bar, I am definitely applying a force (and therefore moment) to the crank end.

Equally the socket end rotates because it is still subject to a torque, but what forces are now acting?

- #12

- 289

- 0

Intermolecular forces. If there's no direct connection, it won't rotate.Equally the socket end rotates because it is still subject to a torque, but what forces are now acting?

Share: