Hi Lou,

You have a long memory :-)


>Oh, I see now. And the thrust of a rocket is only due to the
>pressure within the combustion chamber and has nothing whatever
>to do with the mass ejected from the nozzle, and the kick of a rifle is
>only due to the pressure in the chamber and is not related at all
>to the mass of the bullet fired. That clears up a lot of physical
>effects that are erroneously attributed to Newton, but are in
>fact just pressure problems.

Actually it is a misapplication isn't it. Shooting the bullet doesn't make the gun kick back. Both things are sharing the impulse given by the the explosion. The energy on each is through pressure over the areas involved.

If I am in space setting on an asteroid and toss off a hunk of rock with my arm and hand then I have imparted energy to the system. It is divided into the rock and the asteroid according to masses and inertias. It can be measured by the acceleration of the rock, the rotation and acceleration of the asteroid (with me) or a pressure transducer on my glove measuring the impulse given to both the rock and glove. The fact that I can measure the mass and acceleration of the rock does not mean that it is moving the asteroid. What moved the asteroid is the impulse as measured into the glove - force and time. It doesn't matter if it is a rock or a sping mechanism as long as the impulse is the same.

The same with the rocket and bullet. If you want to measure the thrust of a rocket you put a scale on the nose. Another way would be to measure the pressures acting in and on the rocket and doing a summation of forces. Another way would be to measure the mass and accelerations involved in the exhaust plume. However, if I am measuring the force of the nose of the rocket on the scale it would seem reasonable that measuring the sum of forces on the rocket would be an appropriate thing to measure.

If I want to know what the forces on the wing are measuring the forces (pressures) would be the thing to do.


>Guys, what you say is absolutely true. Pressure is the only force acting
>on the wing. However that force wouldn't exist if the entire pressure
>field surounding the wing didn't accelerate a mass of air downward.

I don't know about this. I always went to sleep in the middle of the lectures I didn't understand. I might reason though that the pressure field is caused by the angle of attack and flow rate. What happens to the flow later is unique but not necessary. However again my math skills are not sufficient to work the problem.