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rotation. why easier when greater r?

rotation. why easier when greater r? - Physics Forum

rotation. why easier when greater r? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #11  
Old 10-30-2005, 09:34 PM
Matalog
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Default rotation. why easier when greater r?


"mumi" <[Only registered users see links. ]> wrote in message
news:dk2v1h$bd8$[Only registered users see links. ].tpi.pl...
everything
words,

Is it not just a law of physics and can't be answered by mere mortals,
leaving God with the responsibliity of answering?




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  #12  
Old 10-30-2005, 09:38 PM
Matalog
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Default rotation. why easier when greater r?

"Matalog" <[Only registered users see links. ]> wrote in message
news:m%a9f.8386$[Only registered users see links. ].net...
The
the

* Change answered for explained and answering for explaining.




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  #13  
Old 10-30-2005, 11:43 PM
tadchem
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Default rotation. why easier when greater r?


"mumi" <[Only registered users see links. ]> wrote in message
news:dk37j8$34s$[Only registered users see links. ].tpi.pl...

In an oversimplified way, he is right:
[Only registered users see links. ]

Torque is *defined* to be the cross product of force and the displacement
from the axis at which the force acts.

When an axis of rotation is involved (as in *all* levers) torque is what is
balanced at equilibrium, and serves as the analog in a rotating system for
simple force in a non-rotating system.

The definition of torque allows a small force to balance a greater one by
acting at a proportionately greater distance (the moment arm) from the
fulcrum (center of rotation).

HTH


Tom Davidson
Richmond, VA


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  #14  
Old 10-31-2005, 10:09 AM
mumi
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Default rotation. why easier when greater r?



for the love of god.
Can you think for a while before writing this kind of thing?
It is not only that you are not helping me but you are
making an impression that you have in fact answered some question
and thus preventing people who may actually have somethin interesting
to say from participating.
Do you belive that the one who created the notion of torque had the power
of god and could change reality by words and definitions? I dont think you
do.
The definition of torque allows NOTHING
but there is SOMETHING that "allows a small force to balance a greater one
by
acting at a proportionately greater distance (the moment arm) from the
fulcrum (center of rotation) "
and i would like to know what the hell that THING is
surely it is not a definition of any kind.





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  #15  
Old 10-31-2005, 01:53 PM
tadchem
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Default rotation. why easier when greater r?


mumi wrote:

As long as necessary...


Excuse me. I though that some correct information and a little
exposition would be helpful.

John was trying to tell you that What you are asking about is *defined*
as torque.


No. He certainly could *model* something of the way the real world
works with a few concepts and mathematical definitions.


I get the distinct impression that you never clicked the link I
provided, or that you were scared off by a few Greek letters.

Let me reproduce the salient part of the page here (in ASCII):

"Torque is defined as t = r x F"

where the t stands for 'torque', the '=' stands for 'is defined to be',
the 'r' stands for 'the length of the moment arm', the 'x' stands for
'times', and the 'F' stands for 'the force'.

Put it all together and it comes out as

"'torque' 'is defined to be' 'the length of the moment arm' 'times'
'the force'"


It is mathematics. Evidently mathematics is a foreign language to you.
I recommend you learn a little. It is widely understood and used by
intellectuals around the world. There are probably more people who
understand 'mathematics' than any other single language in the world.
It isn't very hard. Even 8-year old American kids can understand it,
and they learn how to translate written words into mathematical
'equations' in school.

Tom Davidson
Richmond, VA

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  #16  
Old 10-31-2005, 03:35 PM
Ron Shepard
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Default rotation. why easier when greater r?

I think this is what you are asking. With a lever, you push on one
end and the other end moves. It is geometry, not physics, that
determines the distance that one end moves compared to the other.

The physics comes in when you assign a value of work (energy) to the
distance of movement of one end, and when you assign a value of
force that is applied at the other end. Force is the derivative of
the change in energy (or said another way, energy is the integral of
force over the distance), so the two values must be related through
the geometrical relation. That is, for a given energy change, you
can push with a large force over a short distance, or you can push
with a small force over a larger distance. The geometrical
relationship is what relates the distance you push to the distance
from the fulcrum. It is physics that relates the force and energy
to that distance.

$.02 -Ron Shepard
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  #17  
Old 10-31-2005, 04:30 PM
mumi
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Default rotation. why easier when greater r?

Hereby I define you a stupid dumbass whose dumbassness is diminishing
proportionally with
R where R is the distance from your CRT / LCD (where available). This makes
you quite
intelligent here and there unfortunately we will never know as you will be a
total dumbass
again when if vicinity of your internet-ready computer.

Now get the hell out of my thread.


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  #18  
Old 10-31-2005, 05:53 PM
tadchem
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Default rotation. why easier when greater r?


mumi wrote:

....name-calling and ad hominem attacks simply because I agreed with
someone else, eh?


Whatever *that* is supposed to mean...


You need to post your "No Trespassing" signs more clearly, publish your
registry of the deed, and notify all of those you have intended to
invite to participate in 'your thread.' I see four other names
*besides* yours of participants in 'your thread.'

<plonk>

Tom Davidson
Richmond, VA

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  #19  
Old 10-31-2005, 09:10 PM
PD
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Default rotation. why easier when greater r?


mumi wrote:

Mumi, the fact is that this is another example of an unanswerable "why"
question in physics.

To go back a step, F=ma does not have a "why" answer. There is no
answer to *why* a force is proportional to acceleration, as opposed to
something else plausible but wrong, like (say) velocity or momentum. It
is an *observed fact* that doubling a force doubles the acceleration
and doubling the mass halves the acceleration. Where the content lies,
is in this pattern of *how* nature acts, not *why* it acts.

Similarly, it is an *observed fact* that the same force applied at a
further distance from the pivot increases the angular acceleration, and
Newton's 2nd law for rotation codifies that general rule. Note that I
can make it *plausible* by making arguments that the moment of inertia
is mass*distance^2 and angular acceleration is a/r, and thus we can get
from F=ma to the torque being F*r, but that is a plausibility argument
only. The thing that makes it true is the concurrence with observation.

PD

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  #20  
Old 11-01-2005, 10:08 AM
Matalog
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Default rotation. why easier when greater r?


"PD" <[Only registered users see links. ]> wrote in message
news:1130793046.468560.101010@g49g2000cwa.googlegr oups.com...
by
power
you
one

Exactly. And that is what i mean't by saying that only god will know the
answer, and no-one even replied to me.



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