Which will land first?

[deetyork]

Sure I've just read this somewhere but need the answer verifying or proving false!

If a gun (lets say mounted 6' from the ground & horizontal) is fired (no obstructions) & at the same time an identicle bullet is dropped from the same height as the gun, which bullet lands first?

I seem to think that because Gravity acts equally on both projectiles, they land together. The forward momentum of the "shot" bullet makes no difference.

[chakka35]

That's right.

[Loosehead]

If a projectile is fired parallel to a source of gravity then it is only it's distance, from said source, and speed that decide whether or not it achieves orbit. It therefore follows that the faster or higher that the projectile is fired, or indeed combination of both, the longer it takes to fall to earth. Indeed it is these actions that must be a relief to NASA when trying to achive orbit. I therefore declare that you are emulating the guano of the bovine! 

[Peter Pedant]

Yeah you're right.

The forward momentum (being a vector) has no effect on anything working at right angles to it (gravity)

'proving' it is a different matter - as you normally assume the two things are vectors and then the result follows immediately

[JudgeJ]

This hypothesis would be true if the earth was flat. However, you cannot fire a bullet parallel to the earth’s surface because it is curved. The forward distance covered by the fired bullet means that the earth’s surface becomes further away from the bullet the more it travels forward in a straight line. So it has further to fall to the surface the further forward it travels.

At the relatively low speed of a rifle bullet (about 1200mph) this makes virtually no difference and observations, if they could be taken, would suggest that the two bullets take the same time to fall to the surface. However, if the bullet is fired fast enough the earth’s surface will curve away from beneath it as fast as it falls downwards under the influence of gravity. In this case (ignoring the effect of air friction, which will kill the bullet’s forward speed) the bullet will “orbit” the earth, falling to earth at the same rate that the earth’s surface curves away beneath it.

In practical terms it is not possible to prove this at low altitudes. The speed needed would be enormous and even if it could be achieved the friction of the earth’s atmosphere would slow the bullet down immediately it was fired. At higher altitudes, however, this principle is common. Artificial satellites orbit the earth at various speeds and altitudes. The manned orbiting spacecraft usually travel at around 18,000mph at a height of about 200 miles, completing one orbit in about 90 minutes. The earth’s atmosphere at this height is virtually non-existent and the craft can orbit for years with no propulsion method being necessary once they have achieved the appropriate orbital velocity.

[NetSquirrel]

The two bullets would definitely land at the same time if there was no air present to cause drag.  In reality, though, a bullet passes through the air with much less drag when travelling "forwards" (nose first)  than in any other direction.  So, if you dropped a bullet and it fell nose-first, it would land sooner than one that fell sideways.

The grooves inside the barrel of a gun cause the bullet to spin as it travels.  The spinning keeps the bullet pointing straight ahead (gyroscope effect) to minimise forward drag.  The effect is the same as dropping a bullet sideways as in the example above (it should fall slower).  This leads me to believe that a bullet shot from a gun would land just a tiny bit before a bullet that was dropped.

[deetyork]

Dear Mr Loosehead..................Chill, It aint my theory, I was only asking................have you come back down to earth yet!

[NetSquirrel]

*Tiny bit after.

[al_derenso]

try this.  Throw a marker at your carpet, and where you let go of it, drop the other...thats it.