Everyone has seen pneumatic tube systems in banks and those of you over a certain age probably remember pneumatic tubes in older department stores and even office buildings.
It turns out the technology is quite old and there were great expectations in the nineteenth century. Moving mail and goods were seen as killer applications, but some people worried about moving people.
It turns out that a few atmospheric railroads were built in the first half of the 1800s. Early steam engines were large and it seemed to make sense to have a stationary engine supplying motive power by evacuating a long tube. One wonders what how much longer it would have taken for steam locomotives to appear if the technology for building high quality moving seals was better.
A good project for a rainy day is building an atmosphere canon. The idea is to drop the pressure above a projectile in a tube to the point where the atmospheric pressure at the rear of the projectile is sufficient to (rapidly) move it down the tube.
Find a long piece of PVC pipe (say three feet and a few inches in diameter) and a "T" pipe that is fastened to one end. Find a piece of soft wood or styrofoam that will move down the bore of the tube - ideally the movement should be with little friction, but the vacuum seal should be good - you may want to make some O rings that help make a better fit.
The right angle outlet from the T fitting is attached to a vacuum cleaner hose (I remember using a lot of tape).
To shot a projectile you start the vacuum, put a piece of paper in front of exit at the end near the T fitting and hold the projectile at the far end. At some point the force is great enough that the projectile shoots down the tube, past the T joint and through the paper. My personal best is about fifty feet straight up with a Kirby vacuum and quite a bit of work making the best projectile.
Some tips and comments...
- leaving the bag off the vacuum cleaner generally improves performance
- a streamlined projectile with fins will perform better
- be careful where you use this - it can be remarkably powerful!
Some exercises for the investigator.
- what is the muzzle velocity?
- how big is the pressure drop you get?
- what is the escape velocity to get the projectile past the piece of paper? How much energy is absorbed by the paper?
- does the projectile touch the paper? If not why?
- could you build an energy transfer device where a piston runs down the tube and stikes a projective of equal mass?
Lots of fun!
6:12:37 AM 
|
