Why Does Torque Equal Force for a Torsion Dynamometer?

[quietrain]

does anyone know why for a torsion dynamometer, even though it measures the force, it can still be used as a torque comparison?

FROM
http://www.phywe.com/461/apg/4/pid/853/Torsionskraftmesser-0,01-N-.htm

" 1 PURPOSE
The 0.01 N torsion dynamometer allows to measure small
forces with little friction and without displacement.
A force acting on lever arm 4 is compensated through the
torsion force of a metallic band (torque comparison)."thank you!

 

[S_Happens]

The magnitude of the torque is simply the force multiplied by the length of the lever arm (in meters) when the angle between the lever arm and direction the force is applied is 90 degrees. I'm not sure if you're caught up in some sort of terminology confusion, but this is the standard definition for magnitude of torque, when it is synonymous with "moment" as used in the US (for us Mech. Engrs.).

 

[quietrain]

The magnitude of the torque is simply the force multiplied by the length of the lever arm (in meters) when the angle between the lever arm and direction the force is applied is 90 degrees. I'm not sure if you're caught up in some sort of terminology confusion, but this is the standard definition for magnitude of torque, when it is synonymous with "moment" as used in the US (for us Mech. Engrs.).

yes, i know that , but the thing is for the torsion dynamometer, it measures the force! and somehow that force is proportional to the torque?

does it then mean the length of the lever arm is always a constant and so i can say the forced measured is proportional to the torque?

 

[S_Happens]

OK.

Maybe you're getting hung up on the statement of "...measures the force." This statement is NOT important, and can be misleading. The OUTPUT of the instrument is an indication of what force is applied to the lever arm. This does not mean that it is directly measuring the force and not simply calculating it from the torque and length of the lever arm (and it doesn't matter which way it is done). Like I already stated, and what you said you already "know," there is a very simple relationship between torque and force when the length of the lever arm is known.

The answer to your last question is yes, and good job in recognizing that. Maybe you're not confident in making the assumption that the lever arm is know or must be known for this instrument. From the simple formula, you can see that to solve for one variable you must have the other two. In this case, it is safe to assume that the lever arm is known. Looking at the picture (and being unfamiliar with this piece of equipment), you can also safely assume that the lever arm is what is shown and will not change. If it was able to change, then there would have to be a way for the instrument to know that (a simple calibration).

You say "yes, i know that..." but maybe not as completely as you think. Do not take that as an insult, but a suggestion to think a little bit more about a simple formula. The answer is quite simply...

If you want to calculate force from torque, or vice versa, all you need to know is the length of the lever arm. (assuming the angle between the lever arm and force is 90, and using/calculating the magnitude of the torque).

 

[quietrain]

i see thank you!