Re: My definition of force!!!
From: Don1 (dcshead_at_charter.net)
Date: 03/02/05
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Date: 2 Mar 2005 13:07:46 -0800
PD wrote:
> TomGee wrote:
> > PD wrote:
> > > TomGee wrote:
> > > > PD wrote:
> > > > > TomGee wrote:
> > > > > > PD wrote:
> > > > > > > TomGee wrote:
> > SNIP
> > > > > > >
> > > > But momentum is a quantity that expresses the motion of a body
> and
> > > its
> > > > resistance to slowing down. Here you are again referring to
> > > properties
> > > > while my claim refers to the physical evidence of energy. As
you
> > > > correctly point out, relating velocity to momentum offers no
> > physical
> > > > insight, but that's because velocity is a vector comprised of
> more
> > > > quantities.
> > >
> > > More quantities than momentum? Explain.
> > >
> > > > >
> > More than momentum? Why do you say that? Please try to stay
> focused.
> > I said that momentum is a quantity and velocity contains more
> > quantities of time, speed, and direction.
>
> Perhaps you meant that velocity "contains" quantities of
displacement,
> time and direction (or speed and direction, but not time, speed, and
> direction). Following the same TomGee-speak, momentum "contains"
mass,
> displacement, time, and direction. What the heck is your point?
>
> > >
> > > > > > > > > > >
> > SNIP
> > > > > > > > >
> > > > > > > >
> > > > > > Sorry but that is not germane to our issue.
> > > > >
> > > > > I beg to differ. I maintain that the single key feature of
> energy
> > > > ? is the fact that it is a conserved quantity (and force is
not).
> > > > >
> > > > >
> > > > Well, I disagree, as the truth seems to be a matter of opinion.
> I
> > > > suspect that you are making it an issue simply to veer us
> off-track
> > > > into meaningless blind alleyways which are at the least a waste
> of
> > > > time. Howver, in case you are serious about it, I agree that
> force
> > > > is not a conserved quantity; that is why it is a physical
> > expression
> > > > of the quantity we call energy.
> > >
> > > How can something not conserved be the physical expression of
> > something
> > > that is conserved? The conservation IS the physical expression of
> the
> > > energy!
> > > > >
> > > > >
> > No, sorry, the conservation of energy is a physical law, not a
> physical
> > expression of energy. The physical expression of energy is
observed
> > whenever a force is used. Energy conserved is not energy at work.
>
> I see. So if I heat a gas up at constant volume and raise its
> temperature, where is the force that is being applied to that gas to
> raise its energy? Where is the "expression" of the energy in this
case?
>
> > >
> > >
> > SNIP
> > >
> > >
> > > > Ok, let's take your friction example first. Friction is
> resistance
> > > > encountered by an object moving
> > >
> > > Moving? No, that's only kinetic friction. The case that I
presented
> > was
> > > a case of static friction. Note the car is on a hill but it is
NOT
> > > sliding. It is friction that is holding it even though it is not
> > > moving. I'll give you another example. Pick up a can of peas
> holding
> > > the sides of the can only. What is the force that keeps it from
> > > falling? What is the energy expended in that process?
> > >
> > >
> > Ahem. Pardon me for lying on the floor laughing out loud at your
> > making up definitions! You are beginning to sound desperate. You
> need
> > to read up a little on friction, but first you need to stop making
up
> > things.
>
> I see. So you don't know that friction also applies if the surfaces
are
> not moving with respect to each other?
> Let's try a little experiment.
> Build a little metal ramp, inclined.
> - 1) put a sandpaper-coated puck on the ramp. It does not slide.
> - 2) put a Teflon-coated puck on the ramp. It slides.
> What is the force that keeps the puck from sliding in the first
> experiment?
>
> Repeating earlier example:
> You park your car on a hill. It does not slide down the hill. Why
not?
> (However, in early March you park your car on the same hill when it's
> covered in ice. It slides down the hill. Why?)
>
> > >
> > >
> > > > relative to another object with which
> > > > it is in contact, and resistance is a force that opposes or
slows
> > > down
> > > > another force.
> > >
> > > Actually, no. Did you realize that it is friction that makes a
car
> > move
> > > *forward* when you press the gas pedal?
> > >
> > > >
> > Sorry, but that question only shows you still lack a good
> understanding
> > of what forces are, expecially resistance.
>
> I see. So answer the question, and illumine me.
>
> > >
> > >
> > > > A sign suspended from a beam by cable is under the influence of
> the
> > > > force of gravity on Earth.
> > >
> > > But it is not moving. There is no expenditure of energy! If so,
> what
> > is
> > > it?
> > >
> > > >
> > The force of gravity is pulling on it continuously.
>
> I see. And where does that energy go? Does it heat up the sign?
>
The force has reached equilibrium with the restraining force provided
by the beam and cables. Add some weight - like a nice coat of ice,
and/or the limb of a tree, and plonk. No more question of where the
energy got up and went; it just _went_.
Don
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