Balloons in a Car: The Science Behind Why They Move Forward When You Take Off

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In summary, when a car accelerates, the pressure distribution on the outside of the balloons causes them to move forward due to a buoyant force, regardless of whether they are filled with helium or air.
  • #1
yakabod
You are in a stop light and you have plenty of balloons in the back of your car. The light turns green and you proceed all the balloons move forward. Why when you take off in a car the balloons move forward?





Thanks Alot to whoever answers :)
 
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  • #2
The forward acceleration of the car causes a high pressure in the rear of the car and a low pressure in the front of the car, thus the He balloons float to the front of the car.
 
  • #3
Another way of saying the same thing: The balloons are lighter than air (did you notice that FrankR assumed Helium balloons even though that was not specifically stated- if your balloons are blown up with air this won't happen) and so have less inertia than the air in the car. The air moves backward pushing the balloons forward.
 
  • #4
You can do the same thing in a turn. In an American car if the helium balloon is floating above the front passenger seat and you take a left turn, the balloon slaps you in the face...provided the right window is not open!
:wink:

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  • #5
Originally posted by HallsofIvy
Another way of saying the same thing: The balloons are lighter than air (did you notice that FrankR assumed Helium balloons even though that was not specifically stated- if your balloons are blown up with air this won't happen) and so have less inertia than the air in the car. The air moves backward pushing the balloons forward.

Sure it will... (won't it?)

The innards of the balloon are completely separate from what's going on outside.

When the car accelerates, there is an uneven pressure distribution on the outside of the balloon, which pushes it to the front of the car.

How will the the forces sum to zero if you've got air in the balloon, when they won't if you've got helium in it?
 
  • #6
You don't necessarily need helium filled balloons. It works with air filled balloons as well, as long as there is a buoyant force on the balloon caused by a pressure gradient in the car, since the pressure in the balloon remains constant. I've actually tested both helium and air filled balloons, I barrowed balloons from a kid while riding a car to test a physics principle. I found it actually works better with air balloons, the He balloons tend to stick to the roof of the car, with static electricity and friction because they remain stuck to the roof if you don’t grab them. Saying they're filled with He helps to understand the concept. Just understand where the buoyant force comes from and it's fairly easy to grasp.
 

1. How do balloons in a car move forward when you take off?

When a car accelerates forward, the air inside the car also moves forward due to inertia. The air inside the car pushes against the back of the balloon, causing it to move forward in the opposite direction.

2. Why do the balloons only move forward when the car takes off and not when it's already in motion?

When the car is already in motion, there is no change in speed or direction, so there is no force acting on the air or the balloon. However, when the car accelerates, there is a change in speed and direction, causing the air to move and push against the balloon.

3. Do all types of balloons work the same way in a car?

No, the size and shape of the balloon can affect how it moves in the car. Smaller balloons may not have enough surface area to be pushed by the air, while larger or differently shaped balloons may have different air resistance and move in a different direction.

4. Why do some balloons move more than others in a car?

The movement of the balloon depends on the amount of air inside it. The more air inside, the more force it will exert in the opposite direction when the car accelerates. So, a balloon with more air will move more than a balloon with less air.

5. Can other objects in a car also move forward when you take off?

Yes, the same principle applies to other objects in the car. If there is enough force acting on the object, such as air resistance or inertia, it will move in the opposite direction when the car accelerates. This can be seen with loose objects in the car, such as papers or toys, which may shift or move when the car takes off.

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