How is torque measured?

[sergei]

Also there is the flywheel which by rotational inertia applies torque between the power strokes.

[vvega]

Torque – The measure of the force applied to a member to produce rotational motion usually measured in foot-pounds. Torque is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied.

I already knew this, even before the start of this thread.
That wasnt the nature of the question.

Perhaps I need to clarify myself.
As an example.
A single cylinder 4 stroke engine is spinning at 2000rpm.
A split second before combustion is to occur, how much torque is this engine producing, at this specific point in time?

And how much torque is it producing, at the instant point in time, just after combustion?

Are these two numbers different? yes.

If these two numbers are different, how can you say that the engine is producing xxx amount of torque at 2000rpm?
If you have a 10 cylinder engine that only fires one cylinder at a time, (and you take a measurement of torque at one instant in time) how can all 10 cylinders affect the torque output?

I suppose I could have restated my question as:

How is torque measured, when it isnt applied as a constant force?

there are devises that can do that measurement but the sampling rate has rt o be increadbly high
this makes the device very expensive
it wouls have to sample at least 16 times per second just to give 2 referance points and even then it woudl just be a interpolation of data so hardly acurate as to give you the pulse waveform


v

[vvega]

Also there is the flywheel which by rotational inertia applies torque between the power strokes.

if you were measuring this you would have to remove the flywheel to get a acurate picture.......

just for intrest if you remove the flywheel froma engine and run it your chances of idling is very slim

the inertia has a massive effect on the smoothness of idle

v

[RomanV]

Well to say it bluntly they take value before and after and divide by 2 to get an average.
Say you apply 10 Nm for 10s then 20Nm for another 10s,here is the equation to get Torque out ofthat:
(10Nm * 10s + 20Nm * 10s) / ( 20s) = 15 Nm ! no time componet in result (20s is total time when torque was measured)

can 10nm over 10 seconds be shown as horsepower?
can 20nm over 10 seconds be shown as horsepower?

How is there no 'time' element to torque again? (in the context of the above discussion)

[Caveman]

A seat sitting on a floor will create bending moments across the surface. These can be represented as torques.



oh and FYI im second year mechanical BE

good for you
but flasshing a dgree your not even half way though does not impress me whatsoever

like i said this is 5th form stuff


ill put it simple
if its not a rotational movement it CANNOT be represented as torque

if you wish to argue that the please give me a book title and referance that will back up this

think of it as a paper where you have to give referance for all facts
been at uni and in your 2nd year you will be no stranger to this

http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/RotationalDynamics/DefinitionOfTorque.html

there is my referance
ill give you a online one because you wont have the books i have till you get to your 4th year

v

Ok first off there does not have to be rotation for a torque to be present. For example a torque wrench. You will apply a certain torque to bolt to which point it will stop turning into the thread. Nothing is moving yet a torque is still being applied to the bolt.

Would I be correct saying no rotational movement = no torque? The bolts not moving, however im applying a torque (force x distance) to it.

I dont mind being proven wrong, however, I fail to understand your logic. Maybe we should take this to PM and save daves thread.

And I was simple 'flashing' my half finished degree to show you I have done 5th form physics. Force x Distance is a very elementry and correct statement however often dealing with members, particulary trusses you find moments generated in strange places.

A roof isn't moving, however, exhibits bending moments
http://www2.umist.ac.uk/construction/intranet/teaching/ul222/exp/sfbmdex.htm

I have read your reference and it shows nothing about requiring rotational movement.

[vvega]

Vvega, do you have an answer relating to the example above?

in your example then your talking about adding a time factor
to work it out you would have to use strokes as your datum and work form there

say at 1 rpm you motor produced 30 hp
so we use this forumlar
(HP x 5252) divided by RPM =

30x 5252 / 1 =157560 FTpds



remeber a 4 stroke only provides 1 force stroke the rest is inertia



v

[vvega]

[quote="1998I have read your reference and it shows nothing about requiring rotational movement.[/quote]


im sorry its late
i was tring to make it simple for you since your not getting it

you dont have to have movement to have a rotational force

the torque wrench example is stupid

you are apllying a force about a fulcrum therfore the force is now called torque
but for the fulcrum it would be called force

mate that is exactly what that referance is gave you showed


A roof isn't moving, however, exhibits bending moments
http://www2.umist.ac.uk/construction/in ... fbmdex.htm

this again shows lack of understanding
that movement is along a axis so is force not torque

surely the fact there is no referance to torque whatsoever in that document tells you something

v

[RomanV]

if its not a rotational movement it CANNOT be represented as torque

you dont have to have movement to have a rotational force
v

Not that any of this has much of anything to do with the original question.

there are devises that can do that measurement but the sampling rate has rt o be increadbly high
this makes the device very expensive
it wouls have to sample at least 16 times per second just to give 2 referance points and even then it woudl just be a interpolation of data so hardly acurate as to give you the pulse waveform

Okay, so we're making some progress here.
If this ISNT how they measure torque, then how do they?
How does 10 cylinders worth of torque get measured, (which can only occur over a period of time) without a unit of time being involved?

in your example then your talking about adding a time factor
to work it out you would have to use strokes as your datum and work form there
say at 1 rpm you motor produced 30 hp
so we use this forumlar
(HP x 5252) divided by RPM =
30x 5252 / 1 =157560 FTpds
remeber a 4 stroke only provides 1 force stroke the rest is inertia
v

I know.... this is the exact basis of my original question.
We cant just 'say' that we have 30hp, can we? because we dont know how much HP is produced, until the torque has been measured.

How is that supposed to answer the question anyway? I fail to see the relevance.

Well, it appears that I am going around in circles here.
Which is rather appropriate, considering the topic.

[vvega]

no you have answered it yourself

hp is a mesurement over time
that defines how the torque is measured

if you give a example like i did i.e 30 hp @ 1 rpm
you the define the measurement as a peak over a time

so over this time .. this much rotaional pressure has been applied

some dynos measure hp and then calaculate it back to a torque value were as fivebob said chassis dyno's tend to measure the turing force abd the calculate hp

you have to define the tyoe of measuremenrt to determin the result

if you wanted to measure waveforms in force you woudnt measure it in hp
IMO

v

[vvega]

Well to say it bluntly they take value before and after and divide by 2 to get an average.
Say you apply 10 Nm for 10s then 20Nm for another 10s,here is the equation to get Torque out ofthat:
(10Nm * 10s + 20Nm * 10s) / ( 20s) = 15 Nm ! no time componet in result (20s is total time when torque was measured)

can 10nm over 10 seconds be shown as horsepower?
can 20nm over 10 seconds be shown as horsepower?

How is there no 'time' element to torque again? (in the context of the above discussion)

yes it can but
your not asking for torque now your asking for hp... a measurement that has a time element