Can I set my own bindings?

Walt wrote:

...And someday I plan to get the other two volumes
of Feynman....

There are THREE? I thought there were only two.

--
Cheers,
Bev
----------------------------------------------
"Tough? We drink our urine and eat our dead!"
-- N. Heilweil

Walt wrote:
VtSkier wrote:
Walt wrote:

I cannot find a single definition of torque that
doesn't require motion that is either happening
or is about to happen.


That's odd, since I've only posted it about 5 times. Here it is again:

T = r x F

where F is the force and r is the moment arm vector.

Now, what, exactly, is in motion here? A force, acting on a moment arm
produces torque. We agree that it's possible for a force to exist
without motion. The above definition shows that a stationary force will
produce torque.

I really can't make this any clearer.

If I didn't know you better I'd say that you were just trolling.


The confusion is in the concept of total torque and component
torques. You can apply a component torque which does not cause
motion. In the case of the screw, the torque wrench applies a torque
(indicated by the reading on the wrench) and the screw applies an
equal and opposite torque such that no motion occurs until it breaks
free of the friction. The total torque until the screw moves is zero,
or there would be motion. However, the wrench is still applying a
torque, which is given by the reading.

Would anybody get it if I said, "I need a moment"..

-klaus

lal_truckee wrote:
Walt wrote:

Please see http://en.wikipedia.org/wiki/Torque , or if you're a stickler
for reliable sources, any elementary physics text like Hailliday and
Resnick, or Sears and Zemansky.

Ah, but do you have your copy of Halliday and Resnick at hand?

Well yah. I took physics from Resnick.

-klaus

Walt wrote:
VtSkier wrote:

Here's a more visceral example: pick up a brick and hold it straight
out in front of you with your arm horizontal. Hold it still. Then
please try to explain, without allowing the brick to move, how there
is no torque since there is no motion.

There is FORCE but no TORQUE

Ok. Change the brick out for a ski. Grasp it by the binding and hold it
vertically. Not that hard, is it?

Now grasp it by the tail and (try to) hold it horizontally. Much
harder, right?

Why? What makes one so much harder than the other? The force hasn't
increased, since the ski weighs the same as it did before.

So what makes it so much harder? HINT: torque. I double dog dare you
to hold a ski like that and tell me that you don't feel the difference.

Of course there is a difference. The difference is LEVERAGE and
LEVERAGE is a component of TORQUE. See
http://www.lightandmatter.com/html_b...ch05/ch05.html
which is quoted in a post a little farther down the list.

Walt wrote:
JQ wrote:

Are you two not saying the same thing? Both of you mentioned that to
have torque something must move am I correct?

No. VtSkier is saying that in order to have torque something must
move. I am saying it is incorrect.

That's what you are saying.

Please, let's not get into an argument over whether we're having an
argument. We are, the point of contention is clear.

Walt is quite correct with his analysis of the disagreement.

I guess the difference in your argument is what must move.

NOTHING has to move for there to be torque.

Yes it does.

//Walt

Walt wrote:
VtSkier wrote:
Walt wrote:

I cannot find a single definition of torque that
doesn't require motion that is either happening
or is about to happen.


That's odd, since I've only posted it about 5 times. Here it is again:

T = r x F

where F is the force and r is the moment arm vector.

Now, what, exactly, is in motion here? A force, acting on a moment arm
produces torque. We agree that it's possible for a force to exist
without motion. The above definition shows that a stationary force will
produce torque.

I really can't make this any clearer.

If I didn't know you better I'd say that you were just trolling.

//Walt

It goes to the definition of VECTOR. My reading, which I
posted, it that a vector has magnitude and direction.
Those are the qualities which create a vector, no?

Magnitude is usually expressed as a unit of length.

Force is expressed as a unit like pounds or newtons.
Force, by this definition is static. It takes
movement to make force into work. Or torque.

If you multiply a unit by another unit, you have
created yet a third unit with the first two units
as components of the third.

If you multiply a force (weight) unit by a length
unit you have a third unit that has both weight
and length as components.

if the first two units were pounds and feet the
third unit will be pound-feet. This is a unit
that requires that a force be moved a distance.
If you specify the direction of the distance
and/or add leverage that unit is called TORQUE
as opposed to simply WORK. But the force still
has to move a distance.

Walt wrote:
VtSkier wrote:
Walt wrote:

Force implies torque, torque implies force. Where there is one there
is the other *by definition*. And since we agree that it's possible
to have force without motion it is also possible to have torque
without motion.

No I don't.

You don't what? You don't agree that it's possible to have force
without motion? Or what?

I certainly agree that you CAN have force without motion,
but it's not called WORK or TORQUE. It's simply called
FORCE or weight or the static pull of gravity, but now
work or torque is performed without movement.


http://www.lightandmatter.com/html_b...ch05/ch05.html

Torque distinguished from force

Of course a force is necessary in order to create a torque --- you
can't twist a screw without pushing on the wrench --- but force and
torque are two different things. One distinction between them is
direction. We use positive and negative signs to represent forces in
the two possible directions along a line. The direction of a torque,
however, is clockwise or counterclockwise, not a linear direction.

And then it goes on to add the leverage component of torque.

And I'm not real happy with this guy's definitions either. It feels
like he is confusing force and work/energy by saying, "We use
positive and negative signs to represent forces in the two
possible directions along a line." Which says to me that "force"
as he is using it, has motion/distance associated with it.

I can't say I care much for his presentation either. It suffers from a
common problem: trying to explain physics without vector calculus. When
you try this you wind up dancing around things with vague statements
about directions and magnitudes, everything is done with scalars and
with some hand waving argument about what direction grafted on at the
end. Things get muddy. High school physics, which is usually taught
without calculus, is particularly suceptible to this phenomenon.


//Walt

klaus wrote:
Walt wrote:
VtSkier wrote:
Walt wrote:
I cannot find a single definition of torque that
doesn't require motion that is either happening
or is about to happen.

That's odd, since I've only posted it about 5 times. Here it is again:

T = r x F

where F is the force and r is the moment arm vector.

Now, what, exactly, is in motion here? A force, acting on a moment arm
produces torque. We agree that it's possible for a force to exist
without motion. The above definition shows that a stationary force will
produce torque.

I really can't make this any clearer.

If I didn't know you better I'd say that you were just trolling.


The confusion is in the concept of total torque and component
torques. You can apply a component torque which does not cause
motion. In the case of the screw, the torque wrench applies a torque
(indicated by the reading on the wrench) and the screw applies an
equal and opposite torque such that no motion occurs until it breaks
free of the friction. The total torque until the screw moves is zero,
or there would be motion. However, the wrench is still applying a
torque, which is given by the reading.

Would anybody get it if I said, "I need a moment"..

-klaus

1) Walt? Are you reading this?

2) M(max) = WL/8 is the moment calculation for?

3) Zero Torque = No Motion, So Walt, what you
were saying is that Zero Torque does not equal
the statement "there is no torque". I think we've
just had a word battle. I think we should each
declare victory and withdraw.

VtSkier wrote:

if the first two units were pounds and feet the
third unit will be pound-feet. This is a unit
that requires that a force be moved a distance.
If you specify the direction of the distance
and/or add leverage that unit is called TORQUE
as opposed to simply WORK. But the force still
has to move a distance.

This is where you get confused. Torque has nothing to do with
work. Torque and work end up with the same units, which can lead to
confusion, but which is why work is referred to in pound feet and work
in foot pounds. Work is actually the integral of the vector values of
force dot distance. So the only work done via a torque is via the
force times angle (in radians) over 2*PI*R. So one revolution at
constant 1 pound force gives 2*PI*R pound feet of work. This is
independent of the applied torque, other than the fact that it is the
source of the force.

-klaus

VtSkier wrote:

I certainly agree that you CAN have force without motion,
but it's not called WORK or TORQUE. It's simply called
FORCE or weight or the static pull of gravity, but now
work or torque is performed without movement.


No. If you are using total torque as a basis for motion, total force
is exactly equivalent for motion. You can't have 'em both. You cannot
have a total force if there is no motion, and the motion accelerates
at F/m where F is the total force. Maybe you are getting confused with
non-inertial reference frames and gravity?

-klaus