Hello guys

Just a quick question. We all know that if we fire a bullet into the sky, it will go in a parabolic route (or at least close to it, since the higher it goes from the earth, the less gravity it feels). Now, if we are to fire the same bullet from under the water into the air, how would the route look like?

Thanks for answer.

After the bullet exits the water, it would be same the parabolic trajectory. In the water, well, that's more complex, as you'd have a hell of a shockwave in front of that projectile, although, generally, it would be a parabolic trajectory still. Assuming, of course. the projectile doesn't slow too much, and start tumbling. The speed, length, and rpm of projectiles is very finely balanced, to keep them stable in flight in air, and then unstable, so they refract, and tumble, in more dense mediums (ie flesh).

This of course assumes that your rifle doesn't blow to pieces when you shoot it, because there would be a hell of a lot of backpressure in a barrel filled with water.

fom what I know, a physical object should follow the same overall arc when going from high density to lower density, with some deflection when going from low to high (depending on the amount of difference).

Light is the only thing I know of with a significant refraction effect when changing desities, largely because light seems to follow the path of least time, which is just screwy.

Two different ideas.... hmmm.... I guess I need to ask for another person for another idea.... or experiment....
But to riverwind: How would the route deflection from lower density to higher be? Would it be that the angle made by the water surface and the bullet's route becomes smaller or something?

They're not really different ideas though. phlogistician is just adding that the bullet won't be following a perfect parabola underwater due to the volatility of the medium. It's the same in air too, just less pronounced. Wind currents, humidity pockets, projectile geometry, etc. all affect trajectory somewhat. This is why when a FO calls in a fire mission from a nearby battery they lob a few rounds of smoke and adjust on his order before actually firing HE rounds.

The water would greatly impede the speed of the bullet but assuming that nothing gets in the way of the bullet (current, movement, a fish) then it its trajectory would assume the parabolic shape. Something that can affect the trajectory is buoyancy. While we all know that bullets don't float, everything with mass will be pushed upwards to a certain degree but it may be unimportant with a bullet.

as far as the amount of deflection, I'm sorry to say that I don't know excatly what the numbers would be - this is some stuff we went over in HS physics - I forget alot of specifics.

more than likely taking the equation here:
http://www.pdas.com/bb2.htm
and entering the drag coefficient for both air and water will show the difference in overall trajectory.
Finding the angle of deflection would require knowing at what point along the path the shift from air->water would take place.

Thanks everyone for the info.

I just had another question about this underwater bullet firing, particularly about the effect of the water surface:

1) If the bullet is fired from under the water into the air, would the state of the water surface (rippled or calm) affect the bullet's movement? I simply assume yes, only when the bullet is fired outwards (unless the bullet takes a helluva amount of time before diving back in, the water surface should still be rippled, which is related to the next question), but if it does, in what way?
2) Also, would the surface state affect the bulet's movement if now, it is fired from the air into the water (either shot sraight into the water or lobbed first into the skies)?

Thanks in advance.

SOmehow I dont think the bullet would take any notice of the surface conditions, it would make the surface conditions just before it exits.

What things do you think affect its path? You can figure it out.

Lava