If a gun moving at twice the speed of sound fires a sub-sonic bullet in the opposite direction to which it is travelling… what will happen, will the bullet even leave the gun?
Yes, the bullet will leave the gun at a normal velocity (relative to the gun).
Relative to a person standing on the ground, watching superman fly past at mach 2, firing a gun behind him, the bullet will appear to detach from the gun and trail behind superman at a lower velocity than him, but in the same direction.
Yes; the bullet will attain its normal subsonic speed relative to the gun. To an observer on the ground, the bullet would be moving in the same direction as the gun, but trailing behind it. (Ignoring the effects of air resistance.)
ETA: Yeah, what he said.
Oh noes! Forgot about this relativity lark…
Ok so soon after it leaves the barrel it will begin flying backwards?
And if superman is flying at the same speed as the bullet? It will more or less just drop?
Relative the observer on the ground, it always was travelling in that direction - firing the gun changes the velocity of the bullet by X - so it will either go from a standing start to X, or from a moving start to that velocity plus or minus X (depending on the direction fired).
Yes - that’s pretty much what happens with normal bullets anyway - they don’t fall to the ground any slower just because they’re travelling very fast horizontally.
It will never start flying backwards relative to stationary objects. If you’re standing on the ground, it will always be flying forward, until it falls. Imagine the gun and the bullet as two cars travelling at mach 2 (ie, when the bullet is still in the gun). Then, when the bullet is fired, one of the cars slowly steps on its breaks and begins to slow down until it comes to a stop - ie, until air resistence has stopped the bullet and it falls.
Yes.
By backwards I meant still travelling in the same direction as superman… ie backwards with respect to the direction the bullet would normally move… fired by a non-super… stationary type man
if you misunderstood me there, then I think I get it
crosses fingers
Lets take a more mundane example.
A train is travelling at 25mph on a straight track, on the front of the train, there’s a guy with a tennis ball launcher that shoots balls horizontally at 50mph - there’s another guy, similarly equipped on the back of the train.
Ignoring wind resistance (not a great idea in practice, but never mind), the balls launched at the front of the train move away from the train at 50mph, so an observer standing by the track sees them shoot forward at 25+50mph = 75mph
The balls launched at the back of the train move away from the train at 50mph, so the observer sees them going in the opposite direction to the train, but only at 25-50mph = -25mph (that is, 25mph in the opposite direction to the train)
The train speeds up to 50mph. Now the observer sees the balls launched from the front of the train zooming off at 100mph
The balls launched from the back of the train appear (to the trackside observer) to simply slide out of the launcher and drop straight to the ground. The guy on the train, launching them, still sees them zooming away from him at 50mph.
This only works for physical objects at everyday speeds - once you start talking about light or things travelling at a significant fraction of the speed of light, it starts to work differently.
Gotcha!
Ok thanks everyone! Slightly less ignorant.
For a real life example of the OP’s problem, check out the old B-58 Hustler. It was a supersonic nuclear bomber with a rear-mounted defensive 20mm machine gun. The top speed of the B-58 was about Mach 2, the gun’s muzzle velocity was about the same.
I guess that would still work against anything capable of pursuing the plane - the gun would deposit bullets for the pursuing plane to smash itself into.
Exactly - you can either say that the bomber and the fighter are stationary relative to each other, and the bullets are travelling at their normal speed (assisted by what seems to them to be a Mach 2 tailwind, leaving them no air resistance to overcome), or that the bomber is leaving a wall of bullets in the way of the fighter. If the bullets are in the way, it’s equally bad news for the fighter in either case.
If the bomber is a on a treadmill, and the fighter is on another, things might work out differently.
You are a bad bad bad man.
:eek:
How about a wall of bears?
Take that, Ivan!
But we certainly would never speak of such a thing.
Tris