Measuring Torque: Lever & Torque Wrench Info

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    Measuring Torque
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Discussion Overview

The discussion centers on measuring torque using levers and torque wrenches, exploring the principles of torque, the use of spring balances, and unit conversions related to torque measurements. Participants inquire about the methods and calculations involved in determining torque in various scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant asks how to measure torque exerted on a lever and whether a torque wrench can be used for this purpose.
  • Another participant clarifies that torque is exerted with a lever rather than on it, suggesting that a torque wrench can serve as a lever to exert force about a fixed point.
  • There is a discussion about using a spring balance to measure linear force, with the torque calculated as the product of the force and the distance from the pivot point.
  • Questions arise about using spring balances measured in pounds and how to calculate torque when the force is applied perpendicular to gravity, such as when pushing a door.
  • One participant emphasizes that while spring balances can measure force in pounds, torque should be expressed in consistent units, such as foot-pounds or Newton-metres.
  • A participant inquires about the derivation of conversion factors between different torque units, specifically between foot-pounds and Newton-metres.
  • Another participant provides a brief explanation of the conversion factors involving mass, force, and distance, but does not delve into vectors.
  • One participant asserts that torque is a linear force about a point, which may imply a differing understanding of torque compared to others.

Areas of Agreement / Disagreement

Participants express varying views on the nature of torque and the methods for measuring it, with no consensus reached on the best approach or understanding of the concepts involved.

Contextual Notes

Some discussions involve assumptions about the definitions of torque and the units used, as well as the conditions under which measurements are taken, which may not be fully resolved.

Who May Find This Useful

Individuals interested in physics, engineering, or practical applications of torque measurement may find this discussion relevant.

lizscully
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Hello,
How can I measure how much torque I'm exerting on a lever?
Can it be done with a torque wrench? Or do I need ?
Thanks
 
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A torque is a rotational force about a fixed point so you don’t really exert a torque on a lever, you exert a torque with a lever. Though I suppose there may be a continuous set of torques along its length.

If you can use a torque wrench as your lever to exert your force about a fixed point then hey-presto, job done.

Otherwise you need something that can measure a linear force, such a spring balance, with which you can pull or push your lever. Provided you use your measuring device at a right-angle to your lever, the torque about your fixed point will be the force exerted times the distance along the lever between the rotational centre and the point at which your measuring device is attached.

If it happens to be spring balance marked in Newtons and you measure the radius in metres, your answer will be in Newtons times metres (Nm).
 
Can a spring balance be in "lbs"? Torque = F x r
How would I calculate the Torque in the case that the force applied to the lever is perpendicular to the direction of gravity? e.g. force applied to a door
Is it correct if I multiply the lbs to just the length?
Thank you for your help.
 
Last edited:
Can a spring balance be in "lbs"? Torque = F x r
How would I calculate the Torque in the case that the force applied to the lever is perpendicular to the direction of gravity? e.g. force applied to a door
Is it correct if I multiply the lbs to just the length?
Thank you for your help.

The SI units for torque are Newton-metres. A spring balance could be in lbs in which case it would be conventional to measure the distance in feet (foot-pounds). You can use any unit of force times any unit of length (lifting capacity of an European swallow time the length of your forearm, for example) but then your measurement become less meaningful to other people.

A spring balance measures force, it only coincidentally weighs things if you dangle them – then its measuring the force of gravitational attraction between the object and the Earth.

If your spring balance is horizontal, with no force applied, it will read 0, if you hook one end of it to your door handle and use it to shut the door it will register the force required to shut the door. If you multiply that by the distance between the handle and the hinge, you have the torque applied to the hinge by the handle, through the door.

Not going to get into vectors.
 
How were the conversions derived for: N-m, ft-lb?
If ft-lb is just the length (ft) multiply force (lbs), and N-m is length (m) multiply force (N), how did the conversion 1 ft-lb = 1.356 N come about?
 
A mass of one pound is equal to 0.4536 kg. A force of one pound is equal to 0.4536 kg x 9.81 ms^-2. You now have a conversion factor for the force. One foot is equal to 0.3048 m. Multiply the two factors together, and hey presto!
 
Torque is a linear force about a point.
 

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