physics question

miggillicuddy · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by fleabag

The bullet travels faster than usual!

This has been solved and proved so many times, I cant believe there has been any debate.

Light is one of the few, if not the only thing, that travels at the same speed regardless of the speed the source is traveling at.
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Is that not only because that would be near impossible to prove??

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Shadow_Conspiracy · June 2007

Not if you're off Mythbusters!

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pete700 · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by miggillicuddy

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by fleabag

The bullet travels faster than usual!

This has been solved and proved so many times, I cant believe there has been any debate.

Light is one of the few, if not the only thing, that travels at the same speed regardless of the speed the source is traveling at.
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Is that not only because that would be near impossible to prove??

<hr noshade size="1"><center>~~StumpJumper~~</center>
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No [:p] The speed of light is constant (E = MC, where C stands for Constant and is the speed of light).

I think somebody hit the nail on the head at the start of this thread actually. The bullet wont go any faster, it will just reach it's maximum speed quicker.

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whyamihere · June 2007

And, of course, most of you are wrong.

Most of you are on the rightish lines. But you're wrong. The fastest point for a bullet is when the propulsion has finished, which is either at the end of the barrel, or slightly before it. Air resistance inside the barrel when compared to the air resistance outside the barrel will be negligible, so the bullet will reach the same velocity relative to the barrel regardless of the velocity of the barrel. This is where you were all going wrong, saying that it would reach terminal velocity quicker due to air resistance. This assumes that the bullet accelerates after leaving the barrel, which it doesn't.

So, as you see it, the bullet will leave the gun at the same speed as normal, but decelerate faster after leaving the barrel due to the increased air resistance due to the speed. To a bystander, the bullet will travel faster. If it normally travels 600mph, the bystander will see the bullet leave the barrel at, essentially, 800mph, as long as the bullet is fired in the same plane of motion as the car.

fleabag · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by pete700
I think somebody hit the nail on the head at the start of this thread actually. The bullet wont go any faster, it will just reach it's maximum speed quicker.
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Bol<s></s>locks it will.

The maximum speed of any physical object is the point just below the speed of light where energy is converted to mass, so instead of increasing in velocity, its mass increases.

In other words, a bullet would go faster if more energy was expended in its acceleration. A bigger load of gunpowder would fire it faster.

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pete700 · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by fleabag

Bol<s></s>locks it will.

The maximum speed of any physical object is the point just below the speed of light where energy is converted to mass, so instead of increasing in velocity, its mass increases.

In other words, a bullet would go faster if more energy was expended in its acceleration. A bigger load of gunpowder would fire it faster.

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The maximum speed of any object is when it can't go any faster and will break. The potential speed for any object is just below the speed of light.

I once went to a dyslexic rave and got offered an F
Throw me a beer from the Kula

fleabag · June 2007

Actually, the reference point was never established in the question. I was talking relative to a stationary point, not the gun.

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fleabag · June 2007

How can a bullet break?

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<center>It's in yourdream , There's just one question...Should I kill? kill? Or should I be left behind? </center>

whyamihere · June 2007

Anything can break... Just ask the makers of the Titanic.

pete700 · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by fleabag

How can a bullet break?

<center>- - - - - - - - - - - - Y - o - U - - S - M - e - l - L - - f - U - n - N - Y - - - - - - - - </center>
<center>It's in yourdream , There's just one question...Should I kill? kill? Or should I be left behind? </center>
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Rapid deceleration breaks bullets.

I once went to a dyslexic rave and got offered an F
Throw me a beer from the Kula

sjdrifnfo · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by fleabag

How can a bullet break?

<center>- - - - - - - - - - - - Y - o - U - - S - M - e - l - L - - f - U - n - N - Y - - - - - - - - </center>
<center>It's in yourdream , There's just one question...Should I kill? kill? Or should I be left behind? </center>
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Your joking right?

hazzahulme · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by pete700

The speed of light is constant
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Nearly right. The speed of light in a vacuum is constant.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">as long as the bullet is fired in the same plane of motion as the car.<hr height="1" noshade id="quote"></blockquote id="quote">
It'd have to be in the same direction as motion. You could fire it directly upwards or perpendicularly sideways and it'd still be in the same plane as he motion, but their velocities wouldn't resolve in the way you describe.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Oldmacdonald

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sjdrifnfo · June 2007

I thought terminal velocity was the maximum possible speed you could travel at, when all forces acting on the object were constant. ie a skydiver at terminal velocity would have the force of gravity acting downwards, and an opposite and equal force due to air resistance.

ard nut · June 2007

Yes?

Tom · June 2007

it would be travelling at its normal speed plus 200mph. maybe the wind resistance would have some effect but on an object with that small a surface are and 200mph not actually being that great a speed i doubt it would make that much difference.

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Tom · June 2007

btw i didnt bother reading the rest of the replies so sorry if its already been answered.

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Big Red S · June 2007

<pedantry>

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Red Lemon

It will travel faster than normal initially, but it will decelerate faster than normal too, due to the higher wind resistance. IIRC, wind resistance increases with the cube of velocity, but I could well be mistaken on that.
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It's the square.
Though bullets are (generally) supersonic which complicates things slightly.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by hazzahulme

As far as I am aware, terminal velocity refers to falling objects, and is the speed at which the force due to gravity is equal to the force due to air resistance. There is no external force therefore no acceleration as F=ma.
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Nah, it's where you have two forces acting on a body, one constant and the other increacing. Or both increacing, but one at a rate greater than the other.
Anything propelled through a fluid has a terminal velocity, as the frictions and drags end up equalling the propulsive forces.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by pete700

No [:p] The speed of light is constant (E = MC, where C stands for Constant and is the speed of light).
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c is the conventional letter to use to denote the speed of a wave. The arbitrary constant letter is normally k.

</pedantry>

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ddoogie · June 2007

From some people's explanations it would follow that if the bullet was shot in the opposite direction then it would be going slower than if it was shot from standstill. Which doesn't make sense. Speed up the car to the exact speed of the bullet and shoot it in the opposite direction. Would you reason that the bullet would simply hover in midair or perhaps just flop out the barrel?

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Westie · June 2007

The bullets maximum speed would be just as it leaves the barrel. The bullet can't go any faster than the air resistance would allow untill the drag heats up the bullet and it vaporises. So I rekon the bullet would be traveling 200mph faster than the bullets normal velocity if the gun was stationary. It would immediatley start decelerating when it leaves the barrel and slow down at a rate proportional to the extra 200mph on its velocity.

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whyamihere · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by ddoogie
From some people's explanations it would follow that if the bullet was shot in the opposite direction then it would be going slower than if it was shot from standstill. Which doesn't make sense. Speed up the car to the exact speed of the bullet and shoot it in the opposite direction. Would you reason that the bullet would simply hover in midair or perhaps just flop out the barrel?<hr height="1" noshade id="quote"></blockquote id="quote">To someone at a stationary point of reference, yes, that is what would happen. The person firing the gun, of course, would see the bullet travelling normally.

davesnothere · June 2007

This drive-by shooting business isn't as straightforward as one might imagine.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Tartanyak

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Stuff · June 2007

Im more interested in firing the bullet bacwards out of the car. Say a 450mph muzzle velocity rifle traveling in a magical vehicle that can go 450mph fired out the back. Like an above poster said to a bystander would the bullet simply drop from the end of the barrel?
The forward facing gun thing is quite easy to explain and I think it has been explained many times here using the term relative. To the person firing the gun in the car facing exactly forward in a vacuum the bullet would fly at its max muzzle velocity. So to that person the bullet is traveling no faster as they are still following the bullet at 200 mph. To a bystander though or someone being shot with the bullet (still in a vacuum) the bullet would be travelling at its max muzzle velocity + the 200 mph that it was originally fired at. I base this in a vacuum because then we dont get any wind resistance so things remain constant. If we add air though then the only real change is the air pressure in the barrel might be slightly bigger thus slowing muzzle velocity slightly and after leaving the gun the bullets rate of decelratrion would increase slightly too. So in air the moving gun relatively fires a bullet marginally slower than a stationary gun but thats only based on increased air pressure in the barrel not wind resistance after exiting. If we are not talking relatively the moving gun instantly has a 200mph advantage over the stationary one.
I think the questio should have been worded thus, Relative to a stationary firearm would a bullet fired in the same direction fired from an exact same firearm moving at 200mph travel a)faster or b)slower than the stationary firearm. Explain your findings
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hazzahulme · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Big Red S

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by hazzahulme

As far as I am aware, terminal velocity refers to falling objects, and is the speed at which the force due to gravity is equal to the force due to air resistance. There is no external force therefore no acceleration as F=ma.
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Nah, it's where you have two forces acting on a body, one constant and the other increacing. Or both increacing, but one at a rate greater than the other.
Anything propelled through a fluid has a terminal velocity, as the frictions and drags end up equalling the propulsive forces.
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You're correct of course (as always) but the main reason I was describing it in such a way was because people seem to be confused in this debate about what it is. If you go back to the first page or two, CDC says that the bullet will go no faster than 600mph no matter how fast the gun is travelling when fired as 600mph was the maximum speed of the bullet. This seemed to me to imply that there is something inherent in the bullet that will not allow it to go faster than 600mph no matter the size of the applied force, and other people in the thread started to refer to this as it's terminal velocity. I described it like this in order to give an example of a terminal velocity, however as you point out, it's not the general case and I mistakenly said that it was.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Oldmacdonald

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Big Red S · June 2007

That was just me being pedantic. And the fact that most of the people who irritated me by not seeing that apparently managed to pass the year shows it's not so important.

Also, when working out what is and isn't happening, you are of course interested in the motion of four things: the bystander, the car (and therefore gun), the bullet, and the air you're moving the bullet through.
A lot of people seem to be missing out the air in their 'explanations'.

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hazzahulme · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Big Red S

A lot of people seem to be missing out the air in their 'explanations'.
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Indeed I did that myself, but only because I believe it would be negligible. The air resistance wouldn't make a bullet travel slower than if fired from stationary, but it would make it decelerate faster.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Oldmacdonald

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Big Red S · June 2007

If the air is moving, relative to the gun, in the same direction as the bullet, the air resistance is far, far, lower than if it is moving in the opposite direction. Especially at the high speeds that someone suggested above.

And, given that it's the only decelerating force on the bullet, I'm not sure it can be negligible.

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