jon e prevo
> I have devised an experiment to test the physics
Why are you designing an experiment to prove something you could look up in
any freshmen physics text? For that matter, I think my high school text
covered this.
> of rotational mass in
> relation to 1)work required in linear lb/ft to rotate a wheel and
> 2)additional work required to tow another wheel, same weight, same
> diameter, while exerting rotational force only on the first. I'll let
> you know what my findings are.
That's going to be a problem for a number of reasons:
A) work is measured in lb-ft (or Nm if you prefer metric) not lb/ft. Pounds
per foot would be a measure of how overweight a person is.
B) rotational force, force about an axis, or torque as it is more commonly
called, is also measured in lb-ft, but it's not really the same thing. The
work an engine puts out is best measured by power times the duration run.
C) work is pretty irrelevant to the whole discussion anyway since what we
were debating was the effect of wheel weight on acceleration.
> My postulus is that the added work
> required to move the two wheels in tandem will be less than the work
> required to rotate the first wheel alone.
At constant speed? You're probably right since there are efficiencies in
multiple wheel systems that a single wheel system doesn't have. Most notably
is the distribution of vehicle weight on multiple bearing surfaces. Also, if
the wheel is moving at any reasonable speed, wind resistance on the trailing
wheel will be less.
However, getting back to accelerating the vehicle, the force (just pounds or
newtons, not lb-ft or Nm) required to accelerate a wheel is independent of
how that force is applied.
> Your postulus is that the work required will be equal for both wheels,
> even though rotational force is being applied to only one
> wheel, correct?
If we are talking about force and acceleration, yes. If we're talking about
power and constant speed motion, no. Work is performed in both cases, but
isn't the variable you want to control or measure.
The concept you seem to be missing here (again, check any introductory
physics text) is "conservation of energy". When the rate at which a wheel
spins changes, the energy of that wheel changes. That energy has to come
from (or go to) somewhere. In a car that energy can come from the engine or
go to the brakes. The means by which that energy is transmitted (engine
turns drive shaft, turns drive wheel, pushes frame forward, pushes free
axle, turns free wheel) is only relevant if significant energy losses are
incurred.
In this case, since turning the drive wheel comes earlier in the "power
train" to the free wheel, any such losses would actually make it *harder* to
accelerate the free wheel, not easier. However, I think we can all agree
that these losses are pretty minimal in a well-maintained car. I've never
noticed the body of my car heating up due to non-elastic deformation during
hard acceleration.
Eric Buckley
7 STR: 98 Integra GSR
St Louis Region
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