A ballon in a car.

[xelasnave]

A mate told me today if you have a hydrogen filled (or heilum) ballon in a car that when you accelerate the ballon will move forward and if you brake the ballon move to the rear (opposite direction of travel).
Needless to say if such were so it would help support the notion of a push universe but seriously has anyone any info or views as I thought it would remain stationary.

alex

[GTB_an_Owl (Geoff)]

yes - well i thought it would be the other way round ?

geoff

[xelasnave]

Geoff I am at Drake I think I will select a study group and armed with a cartoon we can do some tests ..someone around here must have some party ballons and a store of helium... however someone must know and no doubt anyone with such knowledge will be a member here.

alex

[troypiggo (Troy)]

I've tried it and it's true. It's to do with momentum of the air in the car, and that air is heavier than the helium in the balloon.

[kinetic (Steve)]

Yep this came up years ago on a Dr Karl session on JJJ radio.
The air 'sloshes' in the car on accelleration so the balloon
goes towards the less dense air.

A few things need clarifying first though Alex,
Is the car owned by a reality TV couple from US?
Is their son hiding in the boot?

Steve

[xelasnave]

I thought it would be true as the guy who told me is credible ...well well how interesting.
alex

[jjjnettie (Jeanette)]

Theoretically...If the balloon was observed from outside the car, you would notice some movement. Observed within the car there would be none.
If the balloon moved while someone was in the car I would assume the the experiment was flawed by the introduction of air currents or such.
It's all relative.

[jjjnettie (Jeanette)]

party tricks

[Omaroo (Chris Malikoff)]

I had this in my final year HSC physics paper at high school, only if was skewed to a left and right scenario.

If the car swerves left, inertia sees the air wish to continue on the original vector - which with a car swerving left around it would "bunch up" on the RHS of the car. Higher pressure there would see the balloon tend left - towards the direction of travel.

Hence, in the fore/aft version here, under braking we'd theoretically see higher air pressure at the front of the car - pushing the lighter density object away - which is rearwards.

[troypiggo (Troy)]

JJJ - it isn't something that's relative to where you are. If you're in the car and accelerate, the balloon moves to the front of the car. If you're outside the car you can still see the balloon move to the front.

[Baddad (Marty)]

Hi Alex,

He is correct. In laymans' terms: The balloon is less dense than the air. As the vehicle moves forward the air is pushed to the rear. The balloon "floats" forward. Pushed by the denser air.

When retarding the reverse happens.

However a balloon filled with air is different. It rides with the air in the car.

Cheers Marty

[jjjnettie (Jeanette)]

My eyes are starting to glaze over now.
As you can tell, physics isn't my strong point. My problem here is that I'm trying to relate it to those thought experiments that HE did all those years ago.

[AstralTraveller (David)]

All very interesting. But I hope you all understand that if anyone on this forum admits to filling balloons with helium I will have to shoot them.

Helium is a finite and quite rare resource that is vital for science and industry. As I understand, it is extracted from oil wells and the only operational plant is in Texas. When it had some problems a couple of years ago there was a world-wide shortage. In my not-so-humble opinion putting it in party balloons is a travesty up there with putting pineapple on pizza.

[Craig.a.c (Craig)]

I will have to give this a go some day, sounds interesting.

Originally Posted by kinetic

Yep this came up years ago on a Dr Karl session on JJJ radio.
The air 'sloshes' in the car on accelleration so the balloon
goes towards the less dense air.

A few things need clarifying first though Alex,
Is the car owned by a reality TV couple from US?
Is their son hiding in the boot?

Steve

That made me laugh.

[Kevnool (Kev)]

Saw this on discovery chanell they were in a minivan with 3 red and blue balloons when they took off they went in different dierctions.
Cant remember what the show was called tho.
Cheers kev.

[Kevnool (Kev)]

here you go see for yourself the question is answered.

http://www.youtube.com/watch?v=aaFn3...om=PL&index=39

Cheers Kev.

[xelasnave]

I see so it depends on the color of the ballon

This problem caused me to go bush for a couple of days and think exclusively about the situation we are considering here...

AND I wondered ..what if we took our ballons (the correct coloured ones of course) out in to space..the voids..where there is nothing ..no air etc... what would happen.

Well the first problem is it would be reasonable to expect the ballon may expand and burst... well would it I wonder.. or if we had a ballon that could expand without rupture then how big would it grow???

So if we had our new large ballon in a space craft out in the voids and performed a simlar test what would happen... presumably the helium ballon would then be a "heavy" ballon and would perform differently...

Still the first question is how large could we expect the ballon to grow before it reached some sort of equalibrium???

and what shape would it find?

I have been looking at the lectures recomended by Nesti and wouldnt you know it when I came to the "inertial frame of reference" being used to work out our math I found I was having problems because I consider there can be no place in the Universe where we can find a place devoid of any outside influence such being the fundamental requirement of such a reference frame... as there will always be something ..even in the voids there is all the energy of the Universe passing by...

Anyways I did wonder how our ballons may act in such a place?

alex