Physics - the bird and the bus

Discussion in 'Off Topic [BG]' started by XtreO, Mar 5, 2008.

1. XtreO

Jan 2, 2008
Norway
Imagine a bird in a parked bus. The bird is at a standstill in midair (say it's a colibri ), it's speed by that being 0 km/h. The bird is thus not touching the interior of the bus. Now imagine the bus accelerating, only driving straight forward (no, it will not crash into anything).

The question is as follows; will the bird hit the back window? The given factors above should be considered only (don't be a nitpicker I mean by that). Present your arguements!

2. thehurlatron

Jan 13, 2004
Holland, Michigan
If the bird isn't moving, I'd think the back window would actually hit the bird.

3. Jiggybass

Nov 15, 2005
No, because I bet the bird isn't dumb enough to just sit there and get hit.

4. Jared LashBorn under punches

Aug 21, 2006
Denver, CO
In reality it wouldn't happen because the bus couldn't accelerate fast enough to make it happen, in your example the bird would theoretically hit the window, just as if you flipped a coin in the air just as a jet was taking off. Not being attached to the bus in any way, it wouldn't move along with it while it accelerated.

5. 5andFretless

Dec 18, 2007
Long Island Ny
This is a realitivity question in a different form. There is no "right" answer, it depends on your reference frame. Lets move on.

6. Brian Jr.

Feb 28, 2007
West Bloomfield, MI
If the bird stays at a velocity of zero in relation to the ground (or, technically, if it keeps a lower velocity in relation to the ground than the bus), yes, the back window will hit the bird. If the bird stays at a zero velocity in relation to the bus, no, the window will not hit the bird.

Luckily for the bird, in my mind it got in through the back window, which is still open. Even if the bird travels much slower than the bus, it's just gonna pass through the open back window.

7. Tsal

Jan 28, 2000
Finland, EU
The question is, does the air inside the bus move when the bus does? If it does, the colibri does move with it, if it doesn't, the colibri hits the rear window. Since you can't feel the rush of air inside a moving bus if the windows are closed, it's safe to assume the air moves with the bus, and the colibri would not hit the window.

8. FL Knifemaker

Apr 9, 2006
Lakeland, FL
It's like jumping just as an elevator starts to go down. If you time it right you would fall all the way to the bottom

9. santucci218

Jan 26, 2007
Pittsburgh
well, only if the elevator fell at the same pace as you, but it will go slower due to the mechanics.

10. Tsal

Jan 28, 2000
Finland, EU
Man, I get that all the time in World of Warcraft - the elevators move practically at the free fall speed :scowl:

11. RedCoatMonster

Aug 14, 2007
Thomas, OK
For the sake of the example, yes he would. It never says the bus is at a stand still, only that the bird is, relative tot he bus. The bus then moves or speeds up, but since the bird isnt attached to the bus in any way he moves independently from it, so the bus moves forward while he is still in the air flying and he will eventually hit the rear window.

12. Jared LashBorn under punches

Aug 21, 2006
Denver, CO
Here's an interesting question that I made extra credit on my students' test a few years back.

I was driving with a friend of mine who thought it was cute to tie a helium balloon (one from a bunch she got from her birthday) to my gear shift so it floated at head level between the driver and passenger seats.

At one point I had to slam on the brakes and everything in the car pitched forward - except the balloon which went backwards. Why?

13. Muusers

tsalĀ“s remarks make sense, therefore he is excluded

14. Brian Jr.

Feb 28, 2007
West Bloomfield, MI
Fluid dynamic effects or none, it's still a question of how fast each moves in relation to a stationary observer. Air displacement can still happen. So if the bus accelerates fast enough, the bird can still hit the back window. Even if the air in the bus is confined. But still, it's a theoretical question, so how it actually happens doesn't really matter.

15. Brian Jr.

Feb 28, 2007
West Bloomfield, MI
Helium is lighter than air. The balloon (helium) still had a forward inertial force, it was just displaced backwards by the heavier air.

16. Brian Jr.

Feb 28, 2007
West Bloomfield, MI
Fluid effects of air. The bird isn't actually moving independently from the bus. He would be "pushed" ever so slightly by the air between the bus and him. Or her.

17. MoD_Scotty

Jul 22, 2007
Thrapston, UK
Maybe if it was that badass dragrace bus that can wheelie the entire 1/4mi.

18. bkbirge

Jun 25, 2000
Houston, TX
Endorsing Artist: Steak n Shake
Air compression (fluid effects) would have little effect in this scenario. As the original poster set the prob up, the bus is parked, the bird is in the air but not moving either. So there's no relativistic effect here that would change the answer, they both start out in the same reference frame. Assuming no other info, like the bird actually has a brain and moves out of the way, the bus moves, bird doesn't, bird pastes the back window, simple.

19. pmarazitiGold Supporting Member

Feb 12, 2006
Singapore
Yes, ok, but what bass the colibri plays?

Well, jokes apart, as it has been said it's a matter of relative speed of colibri with air, the colibri flies in a way to keep a null speed vs. air, therefore assuming that the air will move with bus (acceleration and puntual compression of wave apart) then, as the buss moves, the colibri will move as well... net it won't hit the back window... plus it's a smart colibri...

P.

20. Jared LashBorn under punches

Aug 21, 2006
Denver, CO
Yes, but we are all dancing around the real question here:

What... is the air-speed velocity of an unladen swallow?