Re: [DMCForum] Re: You're both wrong! Attn: Rick/Martin

[Martin Gutkowski <webmaster@xxxxxxxxxxxxxx>]

cruznmd wrote:

>(Is the expenditure of energy, "WORK" even if nothing is moving?)
>In holding the wrench to 20 ft/lbs. and expending energy, are you 
>conducting "work" even though you're not turning the bolt?
>He says yes, "technically". What say you? Consider: If your robot is 
>struggling against an obstacle or another robot, but not moving it is 
>expending energy, but is it working? 
>
I'm going out on a limb here because I'm not entirely certain of my
facts but here goes. "work" is used to describe the transfer of energy.
it can be quantified with respect to time by a measure of "power", or as
a total amount of energy. The word work is purely descriptive, unlike
momentum, inertia, kinetic energy, accelleration, velocity blah blah
blah....

Energy in a mechanical system can only be transferred a certain number
of ways: Heat, Light, Kinetic energy (movement), sound, chemical energy
(charging a battery), or back to potential energy (eg compressing a
spring). No energy transfer is 100% efficient. You're using the word
"work" in the case of doing up a nut in language terms - ie it takes
work to do it. What you are doing is generating heat due to friction,
tensioning the bolt, and compressing the materials involved, all into a
state of potential energy. Until you undo it, it's applying a force to
the two bits of whatever it is you're fastening, but the forces involved
are equal and opposite - no net force, no work done - Newtonian physics.
If you sit there applying pressure to the wrench which isn't moving, are
you transferring energy? Yes. Your muscles are doing all that biology
stuff I don't know anything about involving sugars and creating lactic
acid as a result, but you're transferring energy purely to heat, and
some light (infra red).

If our robot pushed up against the side of the arena, it'd spin its
wheels, pure and simple. The kinetic energy of the drive train, the
noise it makes, the sparks in the motor's commutator generating light,
the incredible amount of heat coming off the motors (even at nominal
load, it's nearly 2kW per motor) and batteries, and  some chemical stuff
happenning between the rubber and the floor which causes the rubber to
melt - all energy transfer.

>BTW, (switching gears here) I love watching Parliament debate. You 
>guys grumble and yell. It has character and reminds me of what 
>congressional debates must have been like centuries ago. Now congress 
>engages in verbal chess, without emotion or candor. Sometimes it's 
>depressing.
>
Watch for Ann Widdicombe - my parents' MP - she always gets a fantastic
reception.... I personalyl have a lot of time for Charles Kennedy. I
like watching the economic arguments banded about. I did A-level
economics and some of the most basic theory floors much of the
governments excuses for policy.

Martin

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