# Looking for a compressed air formula

1. Aug 4, 2010

### VA80232

I know what the formula for the Volume of a cylinder is. If I had say a 25lbs weight and dropped it from the top into the cylinder and lost no air , where would it stop(in inches from the bottom of the cylinder)? Not carrying about temp of the air or moisture. Is their a some what simple formula? I tried to find one on the internet. I would settle for the simplest formula even if it is difficult. Thank you for any help in advance.

2. Aug 5, 2010

### arydberg

You need the area of the piston in square inches. If the area is 1 square inch and the tube is 10 inches from the piston bottom to the bottom of the tube and the experiment is done at sea level the starting pressure is 14.7 psi (p) and the starting volume (v) is 10 cubic inches at the end the pressure in the cylinder is 14.7 + 25 or 39.7 psi. so the final volume (V) is given by pv = PV with the final pressure = (P).

new volume = pv/P = 14.7 * 10 / 39.7 psi = 3.70 cubic inches or 3.7 inches high.

There is a more accurate formuli which is ( p * v ) rased to the gamma = (P * V ) rased tohe gamma.

3. Aug 9, 2010

### VA80232

I see I left to much in question or maybe I can use that same formula?

I am requesting a formula for:

If I had a 100 ft tall cylinder. 2ft wide and 2ft long at the top and bottom equally. A square cylinder. I dropped a 25 pound weight from the top and it free fell loosing no air, at sea level.

How far would it drop towards the bottom before it stopped and held its own weight and how many pounds pressure would the compressed air be left in the cylinder?