# If you could build a train that could travel as fast as a bullet..................
**URL:** https://boards.straightdope.com/t/if-you-could-build-a-train-that-could-travel-as-fast-as-a-bullet/63647
**Category:** Factual Questions
**Created:** [April 28, 2001, 3:43pm UTC](https://boards.straightdope.com/t/if-you-could-build-a-train-that-could-travel-as-fast-as-a-bullet/63647 "2001-04-28T15:43:31Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Jukeball](https://boards.straightdope.com/u/Jukeball)
#### Post date: [April 28, 2001, 3:43pm UTC](https://boards.straightdope.com/t/if-you-could-build-a-train-that-could-travel-as-fast-as-a-bullet/63647/1 "2001-04-28T15:43:31Z")
If you could build a train that could travel as fast as a bullet, what would happen if you fired a gun from a window of a compartement in the train???
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### Author:  [@SmackFu](https://boards.straightdope.com/u/SmackFu)
#### Post date: [April 28, 2001, 4:00pm UTC](https://boards.straightdope.com/t/if-you-could-build-a-train-that-could-travel-as-fast-as-a-bullet/63647/2 "2001-04-28T16:00:48Z")
From the perspective of someone on the train who’s firing the gun, nothing special.
From the perspective of someone on the ground, it all depends on which direction you fire the gun. Fire it against the direction of travel, and the bullet would appear to drop straight to the ground from the barrel of the gun.
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### Author:  [@Amedeus](https://boards.straightdope.com/u/Amedeus)
#### Post date: [April 28, 2001, 4:32pm UTC](https://boards.straightdope.com/t/if-you-could-build-a-train-that-could-travel-as-fast-as-a-bullet/63647/3 "2001-04-28T16:32:08Z")
Ok, im stupid, why would it do that? The wind?
A bullet travels nowhere near the speed of light, so why would the two speeds not add up on top of each other?
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### Author:  [@SmackFu](https://boards.straightdope.com/u/SmackFu)
#### Post date: [April 28, 2001, 4:42pm UTC](https://boards.straightdope.com/t/if-you-could-build-a-train-that-could-travel-as-fast-as-a-bullet/63647/4 "2001-04-28T16:42:10Z")
They do add up. One’s positive, one’s negative, so the sum is zero.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [April 28, 2001, 4:45pm UTC](https://boards.straightdope.com/t/if-you-could-build-a-train-that-could-travel-as-fast-as-a-bullet/63647/5 "2001-04-28T16:45:30Z")
Nothing mysterious here:
A bullet fired in the direction of travel by a passenger would double its’ velocity with respect to the ground.
(eg 4000 fps + 4000 fps = 8000 fps).
A bullet fired by a passenger against the direction of travel would have a velocity of 0 with respect to the ground (4000 fps - 4000 fps = 0 fps).
In both cases the bullet would move away from the passenger at 4000 fps.
If a person on the ground fired a bullet in the direction of the trains travel it would appear to hover motionless outside the trains side window.
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### Author:  [@Amedeus](https://boards.straightdope.com/u/Amedeus)
#### Post date: [April 28, 2001, 4:56pm UTC](https://boards.straightdope.com/t/if-you-could-build-a-train-that-could-travel-as-fast-as-a-bullet/63647/6 "2001-04-28T16:56:48Z")
Ahh, My mistake, I took against the direction of travel as similar as “against the wind” or in the direction one is traveling. That was an error on my part.
**Slaps himself in the forehead**