Drop a bullet vs. Shoot a bullet

[Kyteland]

Originally posted by: spacejamz

can someone explain in layman's terms why the bullet fired from the gun travels at the same speed as the bullet that is simply dropped?

The charge expelling the round out of the barrel would seem to increase the velocity of the round...(the term muzzle velocity also comes to mind)...

Thanks..

You're thinking in therms of absolute velocity. If you break it out in terms of multiple dimentions then it makes more sense. A car traveling due east at 50 mph can have 2 velocities. 0mph in the north direction and 50 mph in the east direction. If that same car is traveling at 50mph in the NE direction then it is going 35mph in the north direction and 35mph in the east direction.

You can do the same thing to a bullet. It is moving up/down according to the force of gravity and forward/back due to the force of the gun. Those two forces are independant. The exact same up/down force acts on both bullets. Different forward/back forces act on them, one fired from the gun one dropped, but this doesn't affect the up/down part. That is gravity all the way.

Basically, the gun has no way of affecting gravity.

 

[hypn0tik]

Given the scope of the question and the typical speeds at which bullets travel and the size of the earth relative to the size of the bullet, we can assume that the earth is perfectly flat in the region the bullet is shot. Curvature of the earth will not have an effect.

As such, neglecting air resistance both bullets will hit the ground at the same time.

 

[MrDudeMan]

Originally posted by: spacejamz

Originally posted by: neutralizer

Originally posted by: spacejamz

can someone explain in layman's terms why the bullet fired from the gun travels at the same speed as the bullet that is simply dropped?

The charge expelling the round out of the barrel would seem to increase the velocity of the round...(the term muzzle velocity also comes to mind)...

Thanks..

The reason the bullet drops is because of gravity. Since gravity pulls in one direction, down. The velocity of both bullets is pulled the same amount because they are dropped from the same height.

that still doesn't make sense...the bullet being fired would have a faster rate of acceleration than the bullet dropped...

you have to break it down into component forces. both bullets have no positive y force (positive being away from the earth) so the only force acting on them in the y direction is gravity. the x force makes NO DIFFERENCE in this case because it is a force in an exactly perpendicular direction. therefore, fired or dropped, they land at the same time (assuming lots of things obviously)

 

[JulesMaximus]

Edit-Oops, I didn't read that the gun was parallel to the ground...

 

[gigapet]

Originally posted by: Bigsm00th

Originally posted by: gigapet

It is always in a state of falling it doesnt hit the ground because there is no...ground to hit because its in outer space....

no its because their orbit is giving them a velocity that is throwing them away from earth at all times, but since gravity holds it in, they stay in orbit without much decay.

should have paid more attention in high school

 

[Argo]

Originally posted by: akubi
well if you consider the curvature of the Earth and its rotation, the answer isn't as trivial as you might think

If you consider curvature of the earth the dropped bullet should be first to touch ground. But then you also need to consider air resistance - the pressure created by high speed of the shot bullet will probably have some sort of effect on its trajectory.

 

[OffTopic1]

Originally posted by: spacejamz

Originally posted by: neutralizer

Originally posted by: spacejamz

can someone explain in layman's terms why the bullet fired from the gun travels at the same speed as the bullet that is simply dropped?

The charge expelling the round out of the barrel would seem to increase the velocity of the round...(the term muzzle velocity also comes to mind)...

Thanks..

The reason the bullet drops is because of gravity. Since gravity pulls in one direction, down. The velocity of both bullets is pulled the same amount because they are dropped from the same height.

that still doesn't make sense...the bullet being fired would have a faster rate of acceleration than the bullet dropped...

Both have Gravity force X exert upon them. Only fired bullet have force Y exert upon it.

We are looking for X rate not Y.

Therefore both would drop at 9.67 m/s/s

 

[Rock Hydra]

Originally posted by: Saulbadguy
Which way is the gun pointed?

At first I was assuming that the gun was pointed downward, since the OP didn't state otherwise.

 

[91TTZ]

Originally posted by: spacejamz

that still doesn't make sense...the bullet being fired would have a faster rate of acceleration than the bullet dropped...

The horizontal component is completely independent from the vertical componenet. Rate of fall has nothing to do with horizontal speed.

The *rate* stays the same, but the distance it must fall can change...

 

[hypn0tik]

Originally posted by: Rock Hydra

Originally posted by: Saulbadguy
Which way is the gun pointed?

At first I was assuming that the gun was pointed downward, since the OP didn't state otherwise.

Uhhhh, perhaps you should read the OP fully??

 

[Lonyo]

Originally posted by: Bigsm00th

Originally posted by: spacejamz

Originally posted by: neutralizer

Originally posted by: spacejamz

can someone explain in layman's terms why the bullet fired from the gun travels at the same speed as the bullet that is simply dropped?

The charge expelling the round out of the barrel would seem to increase the velocity of the round...(the term muzzle velocity also comes to mind)...

Thanks..

The reason the bullet drops is because of gravity. Since gravity pulls in one direction, down. The velocity of both bullets is pulled the same amount because they are dropped from the same height.

that still doesn't make sense...the bullet being fired would have a faster rate of acceleration than the bullet dropped...

you have to break it down into component forces. both bullets have no positive y force (positive being away from the earth) so the only force acting on them in the y direction is gravity. the x force makes NO DIFFERENCE in this case because it is a force in an exactly perpendicular direction. therefore, fired or dropped, they land at the same time (assuming lots of things obviously)

People seem to be thinking the bullet is fired INTO the ground, not parallel to it, which is why they are getting confused.

 

[OffTopic1]

Originally posted by: 91TTZ

Originally posted by: gigapet

so at some point during the journey of the bullet the rate at which it falls is equal or less than zero?

That depends on the speed.

1. Both objects will accelerate towards the Earth at the same rate.

2. The stationary object will fall straight down, impacting the Earth directly under it

3. The speeding bullet will arc, with an orbit (trajectory) dictated by gravity's strength and the bullet's speed. On Earth, the speeding bullet will still impact the Earth's surface since the trajectory will take the bullet in a descending orbit that drops below the Earth's surface. It will hit.

4. However, if you shot the bullet at 17,500 miles per hour, the bullet would never touch the ground, since its rate of descent will match the curvature of the Earth. It would always be "falling" and never hit the ground, since the ground it's vertically falling towards is constantly curving away from it, due to the horizontal speed.

It will hit the ground due to air resistant.

 

[spacejamz]

Let me ask it this way then...

let's increase the height from 4' to 10'...which one would you rather be under? the bullet being dropped or the bullet being fired from the gun?

the bullet being dropped might cause a bruise or something, but probably won't penetrate your skin. However, the result from the bullet being fired from the gun would be significantly different...pretty sure the bullet would pretty much go right through you...

Is this an accurate example?

 

[KoolDrew]

Originally posted by: gigapet
barring no air resistance and gravity remains constant they hit the ground at the exact same time.

 

[Rami7007]

all objects fall at 9.81 m/s squared (didnt look that up )

but the bullet isnt falling, it is being acted on by a force... the bullet being fired would hit first... otherwise they would hit at the same time

 

[gigapet]

Originally posted by: spacejamz
Let me ask it this way then...

let's increase the height from 4' to 10'...which one would you rather be under? the bullet being dropped or the bullet being fired from the gun?

the bullet being dropped might cause a bruise or something, but probably won't penetrate your skin. However, the result from the bullet being fired from the gun would be significantly different...pretty sure the bullet would pretty much go right through you...

Is this an accurate example?

at worstyou get shot in the toe?

 

[acemcmac]

the dropped bullet has no instantaneous velocity, while the fired bullet has a several hundred mph instantaneous velocity at t=0

shouldnt the fired bullet hit first because the dropped bullet has to accelerate first (that whole gravity = 32 thing?)

its a calc problem

I hate calc

 

[MrDudeMan]

i am working the actual physics of this on a piece of paper. give me a minute to write it all down and upload it.

 

[Spike]

Oh man, I read that as dropping a bullet and firing the gun INTO the ground. I was like, WTH, the fired bullet would totally hit first. But if you are firing the gun parallel and you assume flat surface, same gravity, no wind resistence, etc... (basic physics assumption) they would hit at the same time.

-spike

 

[91TTZ]

Originally posted by: spacejamz
Let me ask it this way then...

let's increase the height from 4' to 10'...which one would you rather be under? the bullet being dropped or the bullet being fired from the gun?

the bullet being dropped might cause a bruise or something, but probably won't penetrate your skin. However, the result from the bullet being fired from the gun would be significantly different...pretty sure the bullet would pretty much go right through you...

Is this an accurate example?

Not at all. We are measuring only the vertical component. Ignore the horizontal component.

 

[hypn0tik]

Originally posted by: Bigsm00th
i am working the actual physics of this on a piece of paper. give me a minute to write it all down and upload it.

This I want to see.

 

[MrDudeMan]

Originally posted by: acemcmac
the dropped bullet has no instantaneous velocity, while the fired bullet has a several hundred mph instantaneous velocity at t=0

shouldnt the fired bullet hit first because the dropped bullet has to accelerate first (that whole gravity = 32 thing?)

its a calc problem

I hate calc

no, its a physics problem. well, it could be solved using vector valued functions in calculus, but the theory and mechanics of the operation is physics. i am a physics major.

 

[Delbert]

I think some people are misunderstanding that the dropped bullet is going to go down and the shot bullet is going sideways (perpendicular to earth center) from the same elevation at the same time.

 

[akubi]

please do go on.

i think all physics grads are laughing in tears by now.
:laugh::thumbsup:

 

[Chunkee]

Ask MAME!

That is the answer!