Re: [PSUBS-MAILIST] Isn't 'Mini book review.' anymore--pressure test

[AndrePevestorf@aol.com]

In einer eMail vom 13.04.2002 01:52:55 (MEZ) - Mitteleurop. Sommerze schreibt BluWtrSailr@aol.com:


> In a message dated 4/11/02 5:45:27 AM EST, AndrePevestorf@aol.com writes:
>
> << You will see that you get an average effect and have less stored energy on 
> the one hand but more way to measure the increase... >>
>
> But the rope is not under compression, it is under elongation and its 
> elasticity creates the stored energy.
>
> Charles


Hi Charles,

Do you have an old lawn-mover fuel engine or or a piston pump or a medical syringe or any other stuff that has a good sealed piston in it.? 
If you seal the piston on the head and pull on the cylinder then you will feel a counter force. If you push it in a resistance again. 
Some scientists BOYLE and MARIOTTE played this game a lot of time and the found that the product from pressure and Volume is always the same. (for a constant temperature!) 
What does this mean? If you reduce the volume (push the cylinder in the piston) the pressure will increase in the same way. If enlarging the volume the pressure decrease.
And what is pressure? Itīs a force work on a area. The area of the cylinder is still the same so you have to push with the same effort as you have to pull if you half the piston volume or double it.
If the piston is extrem long and therefor very thin you get something like an air-spring. Pull on such a loooong piston is roughly the same as pull on a rubber rope. (thats the reason why you can fire a pea either wis a rubber catapult or with a soft air gun)

So the conclusion is that air under compression works roughly like a rubber rope under elongation.
And you a right of course, it stores a lot of energy due to his elasticity.

The elasticity from air is the so called "bulk modulus". Steel and other solid metals have a "youngs modulus".
The modulus gives the necessary force to elongate a thin rod to a strain value of 100%. (double the length)
(of course most materials will never reach such a elongation without failure but this is the theory behind the values)

Consider a normal steel spiral spring. The amound of stored energy depends on there stiffness for a given load. 


A.

( Puh... writing such explanations is a jolly good practise for my rusty english indeed...but it sucks!!! The program I use to correct all the misspellings is not very clever... I need often 4-5 trys to get itīs  OK...  .-))