16 replies to this topic

[Stuart]

Think of it as an upside down Tower of Piza and the guy (forgotern his name) dropping two items 'up'. Its air resistance that makes the diffrence. In a vacum, it will reach the same height as deacceleration due to gravity is 9.81 ms-2 with any object on earth (varies with your location).

Stuart

[Gor]

At the risk of being pedantic, air resistance is pretty insignificant when dealing with this sort of mass. It affects a feather because the weight to surface area ratio is so high. (There is also some sense in streamlining a bullet as its velocity is so high, but I doubt if it is worth putting a point on a shell). Robert is right, the inertia is the shells resistance to the pressure generated in the tube.

Also be aware that testing an overweighted shell is pretty useless if your real shell is going to be larger and be fired from a larger tube. The thrust of the charge is generated from the rapid production of gasses and will reduce by the square of the radius of the tube. i.e. 10g BP on a 1" tube will give 4x the thrust of the same amount in a 2" tube (roughly, other factors also come into play). So in crude terms, a 100g shell 2" in diameter will need a different lift from a 1" shell of the same weight to reach the same height.

I hope nobody is looking up when the sand comes down!

Edited by Gor, 02 January 2004 - 11:48 PM.