GUN You know what blows my mind?

Discussion in 'On Topic' started by 993kgt, Nov 24, 2008.

1. 993kgtbuilding an airplane whee

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This is WMD related, meaning, WMD crew will appreciate

Assumptions: rifle is level and parallel to the ground, ground is perfectly flat (no range berms to stop the round)

Statement: if you drop a baseball and fire your rifle, both the bullet and the ball will hit the ground at the same time

This blows my mind. I know it's just physics, but shit

2. Market GardenGuest

The forward motion of the bullet has nothing to do with the effect of gravity on it. Gravity neither knows nor cares that the bullet is moving forward.

3. 993kgtbuilding an airplane whee

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yeah, that's the fucked up part, i get the physics behind it, i just wish it were easier to visualize, maybe i'll get some tracers

4. Market GardenGuest

If we want to be super-ultra specific, the ground would actually have to be curved for the bullet and object you drop to hit the ground at EXACTLY the same time. Since gravity curves spacetime in all directions at once, if we were to have a gravitational source (like the Earth) and we were to draw a plane extending in 2 dimensions from a point on the surface of the gravitational source, the gravitational force would change as we moved from the point at which it touches the sufrace. Since the object dropped (the baseball) would only be exposed to the gravitational force at one point on the plane, the pull would be constant. For the pull on the bullet to be constant, the plane would actually need to curve at the same rate as the curvature in spacetime caused by the gravity of our source.

5. 993kgtbuilding an airplane whee

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that's not true, both the bullet and the baseball are moving through spacetime at the same rate so it cancels out

good job will hunting

6. Willie JNew Member

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its physics. the velocity of the projectile has no affect on the gravity, therefore it still hits the ground at the same time. the bullet head doesnt add lift, which a lot of people assume.
edit: i see that this had already been said. projectile motion kinematics ftw

7. Market GardenGuest

But if you were to fire the bullet at 90º to the spot you were standing, it would, as it travelled forward, move ever-so-slightly away from the center of the gravitational source. The ball dropped only moves towards the gravitational source.

8. Willie JNew Member

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due to the rotation of earth?

V = Vo *sin(x) - gt
x being theta or angle.
Vo is initial velocity
g is gravity (9.8 m/s/s)
t is time

Last edited: Nov 24, 2008
9. Willie JNew Member

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u can prove this just by inserting anything into Vo for two equations(being how fast the projectile is and 0 for the ball). no matter what the initial speed, when u solve for T it will be the same for both. V is the final velocity which is 0 because it has hit the ground

10. david_4x4New Member

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This thread is way to smart for me.

11. Willie JNew Member

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Who has a materials chart for coefficient of friction on a copper coat through air? @ 74 degree F with a 80% humidity

12. Market GardenGuest

Due to the fact that the surface of the earth is curved.

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14. Market GardenGuest

I could draw up charts to show all of it, but reading this is easier...

http://csep10.phys.utk.edu/astr161/lect/history/newtongrav.html

Since the surface of the earth is curved, as we fire the bullet horizontally, gravity acts upon it, but it (the bullet) is also accelerating away from the earth. If we fire it fast enough, it has the velocity to "get away" faster than gravity can pull it back down. Newton's idea was concerned with finding the exact speed that would be needed for the bullet (cannon ball in his case) to enter orbit (it wouldn't touch the ground.) If we were to exceed the speed Newton sought, the bullet wouldn't enter orbit... it would just keep getting further away.

Taking all of this into account, it can be seen that the bullet fired will impact the ground a miniscule amount of time AFTER the ball hits the ground.

15. burstyNew Member

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This is literally like 7th grade science class shit.

16. Market GardenGuest

What part of it?

17. burstyNew Member

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Basic gravity discussion

18. Market GardenGuest

There are a lot of people here that would have failed 7th grade science then.

19. more offModerator

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so the plane takes off ?

20. Market GardenGuest

That has to be the most frustrating internet argument of all time.

21. more offModerator

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dont ever ask that question to a group of people at a party
i did it once and two guys ended up in a fist fight
while 3 girls were screaming at eachother about it
and everyone just left like 20 minutes later all pissed off
(granted they were drunk, but it was hilarious how mad everyone got )

22. AdmittedI shouldn't be on OT right now.

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"At those distances, even the Coriolis effect comes into play"

23. burstyNew Member

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You are not Marky Mark

24. jeepilotBanned

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The interesting thing about long range shooting is accounting for the coriolis force... yes, you have to account for the rotation of the earth under the bullet during time of flight.

for most shots this wouldn't apply since you're actually aiming up at almost anything past about 50 yds. You'd have to get a level on the bbl.

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