Naked Science Forum

General Science => General Science => Topic started by: Schelli on 14/11/2009 03:12:13

Title: If an aeroplane rolls in free-fall, do I turn with the plane?
Post by: Schelli on 14/11/2009 03:12:13

i have been arguing with a friend about something that just came to my mind and i just wanna know if i am right or maybe my thinking and physics understanding is totally screwed.

we talked about doing one of those airplane flights where they simulate zero gravity for a few secs, maybe up to a min or so and i thought it would be so cool while i float in the center the plane would fly a roll and turn around me (of course i am very sure the aircraft performance wouldn't be good enough to do this, but it's just a mind experiment).
now he claimed that it wouldn't turn around me but rather i would turn with the plane which from my physics knowledge is totally wrong. he argued its a closed system and thus if you turn the whole system and i am part of the system that i would turn with it, but that doesn't make sense to me.

the way i think to know this zero g simulation works is that i get accelerated like a cannon ball that you shoot into the air and then the airplane pushes its nose down and i continue my flying curve as i would be a cannon ball and the plane just flies around me covering me from air resistance and stuff.

so basically while in this zero g flight i have no forces acting on me but gravity and of course i got my kinetic energy from the acceleration of the plane - so i am in free fall so to speak. but since no other forces are acting on me (ideally speaking), i would not turn with the aircraft but rather continue on my flying curve without turning.

is my thinking screwed or his ?

greets, Schelli

Title: Re: If an aeroplane rolls in free-fall, do I turn with the plane?
Post by: Geezer on 14/11/2009 03:40:22

I think you are quite correct. You would experience the illusion of zero gravity, but you are actually under the influence of Earth's gravity just as you would be if you were outside the aircraft. As you point out, the aircraft is just moving the air along at the same speed that you are travelling at.

The aircraft cannot "shield" you from Earth's gravity as your friend seems to think. It would be really interesting if it could, but we don't have a way to cancel out gravity. Also, we know rather precisely what gravity does, but there is still a lot of debate about how it does it.

Title: Re: If an aeroplane rolls in free-fall, do I turn with the plane?
Post by: graham.d on 14/11/2009 09:20:12

As Geezer says, you are correct.

Title: Re: If an aeroplane rolls in free-fall, do I turn with the plane?
Post by: Schelli on 14/11/2009 14:01:48

nice, thx for the answers. got a lot more tricky questions we came up with. strange where the mind goes when you start out like that. i ll be posting some more when i got the time.

Title: Re: If an aeroplane rolls in free-fall, do I turn with the plane?
Post by: Karsten on 14/11/2009 21:34:40

Since the airplane is filled with air I would say that you would "begin" rotating very slowly with the plane if(!) the airplane continues to roll. You would not notice this delayed motion after just a few rolls. But I am pretty sure that, depending on the inside surface of the plane, after a two dozen rolls or so you would be rolling with the plane. That would be a mighty ballistic flight curve though.

But do this for your friend: Take a cup of water. Put something that floats in the middle. Set the cup on a record player and begin spinning it. The floater will, depending on its mass, initially keep still, but will begin turning after the cup has rotated for a while. After a while it will turn the speed of the cup. Of course, water is much thicker than air. If you were completely "under" water while in the Vomit Comet you would begin the rolling motion sooner.

Title: Re: If an aeroplane rolls in free-fall, do I turn with the plane?
Post by: Schelli on 15/11/2009 23:06:14

well, yeah. ofc the friction starts to translate the turning motion to the medium you float in and in this case the air will start to turn and sooner or later it will translate this turning motion to you but i dont wanna know how many rolls you have to fly with the plane until you can see the effect. this can take ages :). but good addition to the subject. something you might want to consider for other stuff.

Title: Re: If an aeroplane rolls in free-fall, do I turn with the plane?
Post by: Geezer on 16/11/2009 17:25:49

I suppose it might be rather faster if the "atmosphere" inside the plane is rather viscous, which is not entirely unlikely. After all, they don't call it the "vomit comet" for nothing.