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 Physics and the theoretical
 Hypothetical torque calculation - units sanity check
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mstram
Male New Member
11 Posts


Toronto, Ontario
Canada

(None)

Posted - 07/19/2015 :  4:18 AM                       Like
I've been reading about torque, angular momentum, angular acceleration, and I think I understand the basics. Or do I ? :)

Given :

A (hypothetical) wheel with a m.o.i. of 1 lb*ft^2

Radius of wheel = 1.9099 inches, therefore circumference of wheel = 1 foot

The wheel is at rest, (zero rotation).

A torque of 1 ft/lb is applied for 1 second

Is the result a rotation of 1 r.p.s. (60 r.p.m.) ?

Mike

Edited by - mstram on 07/19/2015 6:48 AM

DataDan
Advanced Member
538 Posts
[Mentor]


Central Coast, CA
USA

Yamaha

FJR1300

Posted - 07/19/2015 :  9:08 AM
Moment of inertia is in units of mass * distance^2.

Torque is in units of force * distance. (And note that this should be expressed as lb-ft, not lb/ft.)

It might be easier to restate in metric units (e.g., kilos and newtons) to avoid this confusion.

Two ways to approach the problem:

1) Torque applied through angle of rotation = work = kinetic energy, from which rotation speed can be calculated.

2) Torque / MoI = angular acceleration, which can be multiplied by time to get rotational speed.
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mstram
Male New Member
11 Posts


Toronto, Ontario
Canada

(None)

Posted - 08/01/2015 :  1:11 PM
quote:
Originally posted by DataDan

Torque is in units of force * distance. (And note that this should be expressed as lb-ft, not lb/ft.)



After much (more) reading / searching it seems to me they should have named the torque unit lb-32p2-ft (pound-force)
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