Bullets and Gravity

[Arese]

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.

What about if you were driving on a conveyor belt?

[hairykrishna]

P9 said:

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

Those are energies, not forces. Once the bullet has left the barrel the only force acting on it, if we neglect air resistance, is gravity.

[Engineer1]

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

What level of physics answer do you want?

Pre A level answer:

they both accelerate towards the ground (on earth) at 10m/s^2

A level answer:

The shape comes in and the air resistance is calculated to account for any reduction in acceleration, this is some nasty none linear stuff with differentiation.

Terminal velocity is the point at which the force of gravity is countered by the drag of the falling object, if the forces didn't cancel the object would still be accelerating.

People saying curvature of the earth matters, I would assume that "local" flatness would have a greater effect, by that I mean is the floor perfectly smooth and level.

[Amateurish]

I don't think that the curvature of the earth does matter. If the bullet is fired at the horizontal then gravity will always act perpendicular to the forward motion.

[P9]

hairykrishna said:

P9 said:

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

Those are energies, not forces. Once the bullet has left the barrel the only force acting on it, if we neglect air resistance, is gravity.

Yes, you are right - I used the term force in the common context rather than a scientific one

[SmoothRB]

Yeah it's like ejaculating horizontally.

[ewenm]

Amateurish said:

I don't think that the curvature of the earth does matter. If the bullet is fired at the horizontal then gravity will always act perpendicular to the forward motion.

Depends how fast the projectile is travelling - if it's travelling fast enough, it won't fall at all and will end up in orbit/heading off across the Solar System. See the Newtonian Mountain link a few pages back.

For bullets and guns however, you can assume the earth is locally flat.

[Frankeh]

To sum up (Having not read any of the thread because it would just annoy me).

In a vacume, yes.
In reality, probably not. There's too many variables.

Still works as a good guide..

[shakotan]

Frankeh said:

To sum up (Having not read any of the thread because it would just annoy me).

In a vacume, yes.
In reality, probably not. There's too many variables.

Still works as a good guide..

[V8LM]

Frankeh said:

To sum up (Having not read any of the thread because it would just annoy me).

In a vacume, yes.
In reality, probably not. There's too many variables.

Still works as a good guide..

Not in a vacuum either as, assuming a rifled barrel, gyroscopic precession of the fired bullet would mean it was not longer level to the ground when it hits hence touches slightly before the free-falling bullet. Then there is the coriolis force that will affect the fired bullet differently from the free-falling one and differently depending on the direction it was fired. Then ther....

[Frankeh]

shakotan said:

Frankeh said:

To sum up (Having not read any of the thread because it would just annoy me).

In a vacume, yes.
In reality, probably not. There's too many variables.

Still works as a good guide..

That I did.

[Ayahuasca]

Simple experiment:

Roll a ball bearing along a table top as fast as you can so it shoots off the end.

As it leaves the table top, drop an identical ball bearing from the table top.

They should both hit the floor at the same time.

[otolith]

Frankeh said:

To sum up (Having not read any of the thread because it would just annoy me).

In a vacume, yes.
In reality, probably not. There's too many variables.

Still works as a good guide..

In reality, approximately yes, near as damn it.

[Engineer1]

It will be close enough, true accuracy would have either the speed of light or the speed of sound factoring in along with reaction time. The science says they both hit the ground at the same time, reality will vary but not by much.

[Size Nine Elm]

ewenm said:

For bullets and guns however, you can assume the earth is locally flat.

I prefer to assume the gun is fired from a height of 1m, and the bullet is dropped at exactly the same time.

But there is a 2m high bump in the ground 10m from the gun. So the fired bullet hits the ground first. QED.