28 Jul
2012
28 Jul
'12
10:27 a.m.
On Fri, 27 Jul 2012 20:33:39 +0100 (BST), ard at p850ug1.demon.co.uk (Tony
Duell) wrote:
I think I've mentioend this before, but both torque and work have the
dimensions of force * distance (e.g. Newtons * metres). But while it is
correct to say that a newton metre of work is a joule, it is incorrect to
do the same for torque. What is the fundamental difference?
-tony
The metre in torque is the length of the moment arm, and mere torque
cannot be work since it is a static quantity and corresponds to the
force in work. To get work from torque you have to multiply by radians,
the angle of rotation over which the torque is applied. Similarly,
power, being work per unit of time, from a motor-car engine is
proportional to torque * rpm.
Not very clearly expressed :-( but you get the idea I hope.
/Jonas
29 Jul
29 Jul
10:48 a.m.
On Fri, 27 Jul 2012 20:33:39 +0100 (BST), ard at p850ug1.demon.co.uk (Tony
Duell) wrote:
Actually, it's more fundamental than that.
Work is a scalar quantity, it's the dot product of the force and distance
vectors. Torque is a vector qauntiity, it's the cross product of the
force and disntance (from the pivot) vectors. For all they ahve the same
dimentions, they are totally different things.
Incidnetaslly, I never met a school maths or physics teacher who realsied
that.
-tony
I think I've mentioend this before, but both torque and work have the
dimensions of force * distance (e.g. Newtons * metres). But while it is
correct to say that a newton metre of work is a joule, it is incorrect to
do the same for torque. What is the fundamental difference?
-tony
The metre in torque is the length of the moment arm, and mere torque
cannot be work since it is a static quantity and corresponds to the
force in work. To get work from torque you have to multiply by radians,
the angle of rotation over which the torque is applied. Similarly,
power, being work per unit of time, from a motor-car engine is
proportional to torque * rpm.
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