Walt wrote:
VtSkier wrote:


Having read the wiki, I don't see much difference
in what I've been saying.

Here are the differences:

You are confusing two distinct concepts, torque and work. They are
different but related ideas. They are *not* the same.

You are saying that torque is not a vector. It is.

You are saying that there must be motion to have torque. Not true. See
below.


In all of the wiki, I can find no instance where
if there is no motion there is torque.


Look again. Here's the definition of torque:

Mathematically, the torque on a particle (which has the
position r in some reference frame) can be defined as
the cross product:

Tau = r X F

where

r is the particle's position vector
F is the force acting on the particle,

So, to have torque, all you need is a force. There does not have to be
motion. It's the cross product of two vectors, so it is by definition a
vector.

From wiki
http://en.wikipedia.org/wiki/Vector_(spatial)
"In physics and in vector calculus, a spatial vector,
or simply vector, is a concept characterized by a
magnitude and a direction."

Further down the page, magnitude is intentionally
used interchangeably with "length" in effect saying
it's the same thing.

Then "magnitude" = "distance", to which you add
"direction" to define "torque" as opposed to "work".
The only difference.

Stated the other way, if there is no motion, there
is no torque.

No.

Think of it this way: I'm testing a binding. I place a boot in the
binding and apply a torque of, say, 50 Newton Meters. The binding
doesn't release. I've just described a situation where there is torque
but no motion. Do you say there is no torque here? If so, how does one
ever test a binding?

You are NOT applying TORQUE to the torque wrench, you are only
applying FORCE of 50 Newtons. There is no TORQUE until there
is movement (of the binding releasing). You are measuring
POTENTIAL TORQUE, which the wrench reads in Newton-Meters
because when the TORQUE happens (by movement) that's what
it will be.

Another example. If I have an object that WEIGHS one pound,
I have to apply a FORCE of at least one pound in the direction
opposite to the FORCE provided by gravity in order to lift it.
There is NO WORK until I have moved the object a distance.
There certainly is FORCE being applied, but until the object
is moved, there has been only POTENTIAL WORK.

By all the definitions you have supplied, both TORQUE and WORK
require movement of a force over a distance.

torque is work in a rotational or angular mode.

Torque produces work when there is motion, according to W = T dot theta
(where theta is the angle the torque moves through and dot is the vector
dot product). The relationship between torque and work is very simple,
but the two are different concepts.

Yes, but look at the definition of VECTOR

Similarly, force produces work when there is motion, according to W = F
dot d (where d is the distance the force acts through and again dot is
the vector dot product). Here force and work are related in a very
simple manner, but that doesn't mean that force *is* work. They are
different but related concepts.

That's correct, but force does not have a movement (distance,
vector, etc.) component.

In particular, force can exist without motion. When that happens, there
is no work. Likewise torque can exist without motion. Again there is
no work if there is no motion.

I've been saying this all along except that TORQUE cannot
exist without motion.

TORQUE is a measure of WORK in a specified direction.

I think the confusion comes in everyday usage as opposed
to scientific usage. Our measuring tools do this to us
also. A Torque Wrench, as you appropriately point out is
notated in measures of torque, newton-meters or pound-
feet. Mine is an old one and is in foot-pounds (exactly
analogous to pound-feet) and I've used the ski shop
wrenches calibrated in newton-meters.

Like the lifting an object example, you apply force
to the wrench and no torque exists until the binding
releases. The potential torque is what you are measuring,
which IS Force, but once again, no torque until the
thing moves (in a rotational way, a vector).