Ok say I am on a train that is going 1000 MPH and am facing the back of the train, now i have a gun and i shoot and the bullet goes out at 1000 MPH, now reletive to me the bullet is going 1000 MPH but what if someone was standing outside the train? Would the bullet stand still? Would they be able to grab it?
Yep. If the bullet velocity exactly matches the train’s velocity in the opposite direction, the bullet will appear to come out of the barrel and fall straight down at 9.8 m/s/s. If he’s standing right under where the gun is fired, he could catch the bullet, if his reaction time is fast enough.
Ignoring air resistance, and ignoring effects caused by the train exceeding the speed of sound (so that it would be dangerous to stand close enough to the passing train to be in a position to catch the bullet): yes, the bullet would just fall to the ground, so if you were very quick, you could catch it.
It would stand still within the line of fire with relation to the ground but still be accelerated by gravity normally.
Disregarding air resistance a ground based camera capturing this in slow motion magically configured to have the gun in the middle of the frame the moment it fires, would have the bullet in the middle of the screen, have the gun “slide off it” as the train moves away, and fairly rapidly fall to the ground.
Now air resistance makes this interesting but practically impossible to predict without further data. The turbulence right behind a 1000MPH train would be complex and would affect the bullet significantly, I would imagine.
On the other hand, you might not want to catch it barehanded. Remember that although the bullet has no linear velocity in parallel to the ground, it still has a large amount of rotational energy–it’s spinning at several tens of thousands of RPM. It would be like trying to catch a drill bit.
and it should be pretty hot too, right?
No, not actually. The exploding gasses in the barrel do get very hot–a few thousand degrees–but the bullet isn’t in contact with them long enough to heat up very much. Right out of the barrel, the back of the bullet will be the hottest part, but thermal conduction will quickly level out the overall temperature to barely warm.
If you’re using a rifle, the bullet will naturally enough be hotter (and faster) when it emerges than from a pistol, considering the longer exposure time to hot expanding gasses. These guys (small pdf document) took some infrared pictures of a bullet from a 5.56mm AR-15 rifle and found at the moment of release, the bullet was a toasty 267[sup]o[/sup] C, not something one would comfortably catch without really thick mittens.
However, the AR-15’s muzzle velocity is actually closer to 2,000 mph. The .357 Magnum is a better choice for a 1000mph experiment. Though I’d expect the bullet to be significantly cooler than the AR-15’s, it’s not something I recommend playing catch with unless you have an asbestos mitt.
Minor correction, the AR-15 is actually a carbine.
Re-reading the OP, it sounds like sager1212 is asking whether the bullet would stand still, as in float in the air, without dropping. Seems to think that a bullet normally is not affected by gravity.
If that’s true, then bullets do indeed fall with gravity. The scope sight is adjusted so that at whatever distance the shooter thinks he’ll be shooting from, the scope points to where the bullet will be at that distance. If you are shooting farther than that distance, the bullet will have fallen and will hit lower than your scope’s crosshairs. My buddies sight in their rifles for around 200 yards, which gives them a nice usable range of 100 to 300 yards of acceptable accuracy.
There’s also the heating due to friction between the bullet and the barrel.
It can be configured as both a rifle or a carbine. Assuming that barrel length is the determining factor.
If you wanted to try an experiment you could get some kind of nerf rocket launcher, figure out how fast it shoots (25mph?), sit in the back of a pickup truck doing 25mph, and launch it straight out the back while an observer on the street watches.
Indeed. Ignoring all other effects, a bullet fired horizontally from a gun on level ground and a bullet dropped out of your hand from the same height will take exactly the same amount of time to fall. One will be hitting the ground rather faster, though.
Nope, the bullet would fall to the ground just as fast as if you had dropped it out of your hand.
Well, on closer reread of my own link, the experimenters used a carbine. It was my mistake to think “rifle” when I saw “5.56 mm NATO round” because I associated it with the C7 rifle, the Canadian variant of the M-16, and the firearm I have the most experience with.
The Canadian equivalent to the AR-15, I mention for the heck of it, is the C8.
In any case, if the shooter on the hypothetical train is firing perfectly horizontally 4.9 meters (16 feet) above the ground, the stationary bullet (and in fact even a moving bullet) will fall to Earth in one second, which isn’t a whole lot of time for it to shed its initial heat. Seems to me the experiment would be just as valid if a softball was tossed off the back of a slow-moving train and we could discount issues of turbulence and temperature.
Yeah, but firing a bullet off the back of a hyper-sonic train is much cooler.
Well, natch.
Y’know, QED there’s an excellent Mythbusters in this. Obviously a supersonic train might be a bit hard to manage, but what about say a fast pickup on a track doing say 100- 150mph and a fairly pissweak bow, which would only fire an arrow about that fast. Develop a mechanical bow firing rig setup on the back of the pickup so that you can have a consistent firing speed, get the pickup up to the right speed and (as you pass the slowmo camera) fire. Cool shot from the pickup of arrow firing normally and zinging off at 150mph, cool shot from side on of the arrow falling to the ground.
Or alternatively, build a minature vehicle (perhaps a train mockup) that you can get to a silly speed and fire the lowest muzzle velocity gun you can find off the back of it. I don’t know if that’d be practical.
Not that this was the question, but wouldn’t the bullet be going 2000 MPH relative to the person on the train? If the train is going 1000 MPH forward, and he just dropped the bullet with no horizontal velocity, he would move away from it at 1000 MPH, but since the bullet is going another 1000 MPH in the opposite direction, wouldn’t it be getting further away at 2000 MPH?