Please can someone explain the classic helium balloon in a car?

What sorcery is this?!

Thank you!

Motorbiker

x

O_O

Original post by Puddles the Monkey

What sorcery is this?!

Thank you!

Normally when accelerating, you are thrown backwards. I assume the helium balloon goes forwards because it is lighter than the surrounding air, and so the air going back wrt to it makes it go forwards.

Reply 3

Slowbro93

20

Original post by Puddles the Monkey

What sorcery is this?!

Thank you!

Isn't it down to the balloon moving at a slower velocity to the car so as such it's now experiencing the movement in that particular direction? :holmes:

Reply 4

rayquaza17

17

Is this not what normally happens to people in cars, but the helium balloon has less mass and so the effects are more obvious??

Posted from TSR Mobile

Reply 5

JakeW1000

1

Saw this a while back. Hope it helps.
https://www.youtube.com/watch?v=y8mzDvpKzfY

Reply 6

Puddles the Monkey

OP

Original post by rayquaza17

Is this not what normally happens to people in cars, but the helium balloon has less mass and so the effects are more obvious??

Posted from TSR Mobile

I normally get pushed backwards into the seat when a car accelerates. Heavy breaking throws you forwards.

The balloon goes in the opposite direction!

Reply 7

mphysical

14

Air is a fluid so sloshes around with the movement of the vehicle and is still moving when the vehicle stops, more so than the occupants because it is lighter.
As the car accelerates the air is being forced (more dense) into the rear of the vehicle
The balloon moves towards the less dense air in the car (front) because the higher density air forces it that way.

Reply 8

Original post by Puddles the Monkey

What sorcery is this?!

Thank you!

When you brake all the air rushes to the front, pushing the balloon backwards.

Reply 9

Original post by Puddles the Monkey

I normally get pushed backwards into the seat when a car accelerates. Heavy breaking throws you forwards.

The balloon goes in the opposite direction!

You're heavier than air.

The balloon is lighter than air.

Heavier things go forward, therefore logically, lighter things must go backwards.

Reply 10

Motorbiker

Original post by mphysical

Air is a fluid so sloshes around with the movement of the vehicle and is still moving when the vehicle stops, more so than the occupants because it is lighter.
As the car accelerates the air is being forced (more dense) into the rear of the vehicle
The balloon moves towards the less dense air in the car (front) because the higher density air forces it that way.

This is the only explanation i've found that makes sense. It's what i was told yesterday as well.

Reply 11

Original post by Motorbiker

This is the only explanation i've found that makes sense. It's what i was told yesterday as well.

Unfortunately its *******s.

If the air was "sloshing around" as the car moved, you would feel it, wouldn't you. It would be like being outside on a windy day.

Gravity and acceleration are equivalent. Hence anything that rises under the force of gravity is correspondingly going to go in the opposite direction under acceleration.

Reply 12

Motorbiker

Original post by cole-slaw

Unfortunately its *******s.

If the air was "sloshing around" as the car moved, you would feel it, wouldn't you. It would be like being outside on a windy day.

Gravity and acceleration are equivalent. Hence anything that rises under the force of gravity is correspondingly going to go in the opposite direction under acceleration.

Well, air obviously is moving around somewhat as that's how gases work.

That final part makes good sense though.

Reply 13

Original post by Motorbiker

Well, air obviously is moving around somewhat as that's how gases work.

That final part makes good sense though.

If there was no balloon in the air, would the air move? If so in which direction?

Reply 14

Motorbiker

Original post by cole-slaw

If there was no balloon in the air, would the air move? If so in which direction?

Would there not still be a higher density of air briefly in the back of the car during acceleration?

Reply 15

purple-duck

15

Original post by cole-slaw

Gravity and acceleration are equivalent. Hence anything that rises under the force of gravity is correspondingly going to go in the opposite direction under acceleration.

I swear this doesn't make any sense :s-smilie:

The balloon is still pulled down by its weight - it isn't some weird opposite force object!?
By that argument if you blow the balloon (apply a force/acceleration to it) then it should go towards your mouth/where you're blowing from. I don't think that would happen :colondollar:

Reply 16

Original post by Motorbiker

Would there not still be a higher density of air briefly in the back of the car during acceleration?

A very, very slight one. The accelerative force backwards would not override the gas pressure enough to maintain a significant pressure gradient from back to front.

Assuming that some physical objects in the car move backwards during acceleration, the net movement of the air molecules is probably actually forward.

Reply 17