Accelerate quickly in your car and any objects or people inside will be forced backwards, but a helium balloon actually goes forward. Why?
The reason you are lunged against the back of your seat when you slam on the gas is because the vehicle is suddenly moving much faster than you were at a resting state. Alternately, slam on the brakes and you and anything in your car will fly toward the front. Seat belts, they’re important!
However, inflate a helium balloon and put it in that same vehicle and it will do the exact opposite of you and every other loose object in the car.
It’s perplexing to see, until you begin to understand the simple reason that it happens.
Smarter Every Day host, who we’ll call Destin (because that’s his name), explains what is going on with the helium balloon in his minivan demonstration.
Every other object in the van moves under the laws of physics, but the helium balloon and the invisible air around it are actually acting under the laws of fluid dynamics.
In the video, Destin fills a mason jar with water, leaving an air bubble at the top. As the jar is propelled forward, the heavier water sloshes toward the back, which pushes the much lighter air bubble to the front. The lighter air bubble is simply at the mercy of the behavior and force of the heavier water.
The exact same thing is happening with the helium balloon in the minivan, except we can’t see the heavier force in this instance like you could the water because the heavier force is now the air.
As we all know, helium balloons float because helium is lighter than air. So when the van is propelled forward, the heavier air is forced toward the back of the van just the same way the water was in the jar. This pushes the lighter helium balloon forward.
So technically, the helium balloon is not actually moving forward, rather, it’s being pushed forward by the invisible force of the air sloshing behind it.
There you have it. Now, if you’re ever bringing helium balloons with your kids to a party, you can impress them with your knowledge during the ride!
Source: SmarterEveryDay