Bullets and Gravity

[OnTheOverrun]

Alfanatic said:

OnTheOverrun said:

ewenm said:

OnTheOverrun said:

ewenm said:

Conveniently missing the "fired horizontally" aspect of the original scenario

I didn't miss it - it even states the drop.

It does, but the sniper's bullet has an vertical component of motion which is the point of "fired horizontally" - no vertical component of initial motion.

If you threw the "dropped" bullet vertically upwards with the same component as the fired bullet, then they'd take the same time to hit the ground.

Edit for mis-spelling component TWICE!

Edited by ewenm on Tuesday 1st June 15:00

You're kinda missing the point of my post with regard to the actuality of the physics being so obviously counter-intuitive to some on here, but. . . . .

Why would you need to throw the bullet upwards when it was fired from above the target on a downward trajectory?

I'm sure I'm missing the hidden meaning behind your winks... but I'll bite anyway. Would I be correct in assuming that if the bullet had dropped 120m before hitting the target, then the shooter's barrel was aiming at a point 120m above the target when they took the shot? So, either he fired horizontally from a piece of ground 120m above the ground the target was on, or he was on the same level but the gun barrel was pointed upwards (i.e. not a horizontal shot), or some combination of both, but whatever his initial relative altitude was, he fired at a point 120m above target?

Just missing it a bit - I understand how it works but I've been playing devil's advocate and giving lots of very reasonable and intuitive examples of why it shouldn't work the way it does. . . . . .

[rypt]

Ayahuasca said:

rypt said:

TonyHetherington said:

ysnnim said:

Surely the fired bullet has two forces being applied, both the force from the 'firing' of the bullet, in the horizontal direction and the gravitational one.

Consider only the vertical forces; i.e. gravity. Both bullets have exactly the same acting upon them.

The bullet could potentially generate some lift due to temperature variations in the air

Edited by rypt on Tuesday 1st June 20:47

Run that by me again?

Imagine firing a bullet where half the bullet is in warm air, half in cold air ... different densities, hence different lift above/below ...

[Ayahuasca]

rypt said:

Ayahuasca said:

rypt said:

TonyHetherington said:

ysnnim said:

Surely the fired bullet has two forces being applied, both the force from the 'firing' of the bullet, in the horizontal direction and the gravitational one.

Consider only the vertical forces; i.e. gravity. Both bullets have exactly the same acting upon them.

The bullet could potentially generate some lift due to temperature variations in the air

Edited by rypt on Tuesday 1st June 20:47

Run that by me again?

Imagine firing a bullet where half the bullet is in warm air, half in cold air ... different densities, hence different lift above/below ...

But that effect (insignifiant as it would be) is just as likely to push the bullet downwards, or sideways as upwards.

[FasterFreddy]

rypt said:

Imagine firing a bullet where half the bullet is in warm air, half in cold air ... different densities, hence different lift above/below ...

This is starting to get a bit far-fetched.

There are all sorts of conditions which could affect the time it takes for each bullet to hit the ground, but we have to make the assumption that the air density, temperature, humidity, bullet weight, bullet shape and hundreds of other potential variables are equal and if they are, the bullets will hit the ground at the same time. Give or take a bit.

[SystemParanoia]

why not just say we're on the moon in a man sized polythene bubble of air

[FasterFreddy]

SystemParanoia said:

why not just say we're on the moon in a man sized polythene bubble of air

OK

"We're on the moon in a man sized polythene bubble of air"

[Ayahuasca]

FasterFreddy said:

SystemParanoia said:

why not just say we're on the moon in a man sized polythene bubble of air

OK

"We're on the moon in a man sized polythene bubble of air"

Cool, man. Far out.

[SystemParanoia]

party time!

[WorAl]

Pesty said:

johnfm said:

shakotan said:

WorAl said:

Don't forget this must be performed with bullets of the same weight. So if you are going to experiment you have to take the tip out of the cartridge if using a real bullet. Air rifle probably better to use.

Physics fail...

+1

he is joking right?

No I wasn't actually, I was under the impression that one of the objects would accelerate faster than the other? In a vertical direction. (because of air resistance etc) Therefore one would cover the distance faster than the other?

I am happy to be told otherwise. As it's years since I've done any physics and I have a memory like a seive.

If it is the case that they accelerate at the same rate, would one have a greater terminal velocity than the other? And that is where I'm getting confused?

Edited by WorAl on Wednesday 2nd June 00:15

[tenex]

rypt said:

Imagine firing a bullet where half the bullet is in warm air, half in cold air ... different densities, hence different lift above/below ...

A cross-wind generates lift/ drop. It was a well known effect when I used to do a lot of target shooting.( R/L wind down L/R up. Right handed twist IIRC ).
I'm sure I'll be corrected if wrong. There are some clever people on this thread.
I'm b*****ed if I can remember the name. That's senility for you!


And yes, the bullets/shells would hit the ground at the same time.

[zakelwe]

The bullet will always hit the ground slightly later than the one dropped, unless you live on a planet with zero curvature (unlikely).

Andy

[Alfanatic]

WorAl said:

Pesty said:

johnfm said:

shakotan said:

WorAl said:

Don't forget this must be performed with bullets of the same weight. So if you are going to experiment you have to take the tip out of the cartridge if using a real bullet. Air rifle probably better to use.

Physics fail...

+1

he is joking right?

No I wasn't actually, I was under the impression that one of the objects would accelerate faster than the other? In a vertical direction. (because of air resistance etc) Therefore one would cover the distance faster than the other?

I am happy to be told otherwise. As it's years since I've done any physics and I have a memory like a seive.

If it is the case that they accelerate at the same rate, would one have a greater terminal velocity than the other? And that is where I'm getting confused?

Edited by WorAl on Wednesday 2nd June 00:15

Firstly, I don't think they would, since they're both showing the same profile to the vertical component of their motion. Secondly, since they'll be dropped from a height of around 4 feet or so, neither has enough room to reach terminal velocity or even, I would think, a vertical speed component that is fast enough to make a significant aerodynamic effect. The fired bullet's forward motion may impact its vertical drag properties and The Mythbusters may have been wrong if you take their results all the way down to very tiny fractions of a second but I think they do prove that the theory behind the claim is sound and the two bullets fall to earth at almost exactly similar rates.

[WorAl]

Ahhh yes I know that, my question turned to a more general question of freefall physics.

What would hit the ground first, a tennis ball or a cow? Given enough room to reach terminal velocity if required.

Edited because of stupid bloody iPhone.

Edited by WorAl on Wednesday 2nd June 08:52

[Alfanatic]

Ah sorry, I misunderstood

[Lord Flasheart]

Just to mess with peoples heads a bit more. If the rifle was travelling forward at the muzzle velocity of the round and the round was fired backward it would hit the ground directly under the point at which it was fired from.
To simplify that, if you were driving a pickup at 60mph and fired a ball back in the direction you have just come from at 60mph the ball would drop vertically as the forward motion of the truck cancels out the rearward motion of the ball, so if you dropped another ball (or bullet) at the same time as you fired the one from the moving vehicle, both would hit the ground at the same time.

[Strangely Brown]

Lord Flasheart said:

To simplify that, if you were driving a pickup at 60mph and fired a ball back in the direction you have just come from at 60mph the ball would drop vertically as the forward motion of the truck cancels out the rearward motion of the ball

Yup. Mythbusters have done that one too.

[shakotan]

Lord Flasheart said:

Just to mess with peoples heads a bit more. If the rifle was travelling forward at the muzzle velocity of the round and the round was fired backward it would hit the ground directly under the point at which it was fired from.
To simplify that, if you were driving a pickup at 60mph and fired a ball back in the direction you have just come from at 60mph the ball would drop vertically as the forward motion of the truck cancels out the rearward motion of the ball, so if you dropped another ball (or bullet) at the same time as you fired the one from the moving vehicle, both would hit the ground at the same time.

That's not really messing with peoples heads though, that's just logical.

[hairykrishna]

I actually thought that the Mythbusters experiment to demonstrate this (the bullet drop, not the pick up one) was a bit of a shocker. What they essentially demonstrated was that their set up wasn't really good enough to provide conclusive data.

Edited by hairykrishna on Wednesday 2nd June 11:31

[WorAl]

I would like to add that the kick of the gun in the mythbusters experiment would have raised the trajectory of the bullet slightly.

[P9]

2 forces come into play; kinetic energy & gravitational potential energy. The other factor is the mass of the object.

The kinetic energy from the gun will disipate and leave the bullet subject to the 2 forces above.

HTH