On Sat, 04 Oct 2003 14:26:36 GMT, "Bob Swinney" wrote:
Richard J Kink sez:

"...No, you said, "Torque is the capacity of an engine to do work", which is
just wrong..."

Uh huh. And would you care to comment on exactly how that statement is
wrong? Torque is a turning moment that defines the force applied to a shaft
in order to do work. Without torque the shaft cannot turn, work cannot be
done.

Mechanical work is defined as the product of the applied force and the
resulting load displacement (distance) *in the direction of the applied force*.

(see Machinery's Handbook, page 92 of the 24th edition, or any good
elementary physics book)

Torque is defined as the product of the applied force and the length of
the lever arm against which it acts. The latter is at *right angles* to the
applied force, and hence the product is *not* work according to the
definition of mechanical work.

You can apply any arbitrary torque and still not do any work, consider
pulling on a wrench applied to a stuck fastener. No matter how hard
or long you pull, you've done no work (in the physics sense) until the
fastener moves.

Power determines the rate of doing work, and over any given period,
the capacity of the system to do work. (We're implicitly assuming a
prime mover fuel tank sufficiently large to maintain that power input
over the given period, of course.)

Note that it is implicit in the definition of power that the shaft *is*
turning. Unlike the case of torque, displacement at some rate is
required, otherwise no work will be done.

Gary