Re: .Bernoulli and curve balls.

[palmer@sfu.ca (Leigh Palmer)]

> Ah Rick,
> You used the important words... Conservation of energy, conservation of mass,
> continuity equation.  This is why Bernoulli's principle works, this is what
> Bernoulli's principle is about!  If we have an incompressible fluid in a pipe
> and the pipe gets smaller continuity says to get all the fluid through the
> smaller pipe it has to go faster.  Now if it is going faster it has more
> kinetic energy.  Conservation of energy says this energy came from somewhere.
> Where?  Why the random motion of the molecules that make up the fluid.

No! There is work being done on the fluid by the force of the pressure
integrated over the cross-section of the pipe*. The power generated by
this work shows up in the increased kinetic energy of the flow. Your
suggestion lies perilously near a violation of the second law of
thermodynamics.

> They
> now have more motion in the direction of flow and less motion in other
> directions.  This means they can't bang on the pipe as much or as hard so they
> exhert less pressure on the pipe.  Now if the pipe gets bigger they don't
> go forward as much, have more random motion and beat on the pipe more.  This is
> what Bernoulli's law is all about.

That should be very easily understood by 99% of students. It may even
befuddle the other one percent. Is that what you want to do? Why lie
when the correct answer is so accessible?

Leigh, the rude dude

*Of course it is the sum of the work being done at both ends of the
fluid in question.