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sirgilligan · October 18, 2014, 08:29 PM

Yes, the gravitational constant is different at different altitudes. In my ballistics calculator I do correct "gravity" for altitude, but I only do it at the beginning of the calculation because typically we are looking at bullet drops in inches and maybe up to a yard or so for typical shooting.

Currently the calculator uses a stepping algorithm.
The bullet starts with a certain muzzle velocity, ballistic coefficient, sight height and bore axis.
Then I calculate where how long it takes the bullet to travel an inch. That time is time of flight. With that time I can calculate how far it dropped. I also calculate how much the bullet slowed down due to drag. Now the bullet is moving slower and I calculate how long it now takes it to travel an inch. The process repeats over and over, recalculating each step.

If I wanted I could recalculate gravity for each step as well, but it doesn't really matter for such small changes in height above the center of the earth.

Falling objects
http://youtu.be/zMF4CD7i3hg

This one is really fun:
http://youtu.be/D9wQVIEdKh8

Objects in a vacuum
http://youtu.be/AV-qyDnZx0A

And here is the one I remember from College, my favorite:
http://youtu.be/cxvsHNRXLjw

October 18, 2014, 08:29 PM	#23
sirgilligan Senior Member Join Date: October 28, 2009 Posts: 614	Yes, the gravitational constant is different at different altitudes. In my ballistics calculator I do correct "gravity" for altitude, but I only do it at the beginning of the calculation because typically we are looking at bullet drops in inches and maybe up to a yard or so for typical shooting. Currently the calculator uses a stepping algorithm. The bullet starts with a certain muzzle velocity, ballistic coefficient, sight height and bore axis. Then I calculate where how long it takes the bullet to travel an inch. That time is time of flight. With that time I can calculate how far it dropped. I also calculate how much the bullet slowed down due to drag. Now the bullet is moving slower and I calculate how long it now takes it to travel an inch. The process repeats over and over, recalculating each step. If I wanted I could recalculate gravity for each step as well, but it doesn't really matter for such small changes in height above the center of the earth. Falling objects http://youtu.be/zMF4CD7i3hg This one is really fun: http://youtu.be/D9wQVIEdKh8 Objects in a vacuum http://youtu.be/AV-qyDnZx0A And here is the one I remember from College, my favorite: http://youtu.be/cxvsHNRXLjw __________________ SirGilligan - "If you find your back is up against a wall, maybe you have been backing up for too long." iOS Apps: BallisticsGL Gun Log Gun Log SPC WatchForce Last edited by sirgilligan; October 18, 2014 at 08:42 PM.