You work for a balloon delivery service and you are delivering a single, helium-filled balloon in your car. To prevent the balloon from bouncing around on the ceiling while you are driving you have tied a string with a weight on it to the balloon. The weight is resting on the floor and the balloon is floating just below the ceiling.

When you accelerate, does the balloon stay where it is, move backward, or move forward? What does it do when you make a turn?

Assume all the windows are closed and the vents are turned off so there is no air flow inside the car to affect the balloon.

interesting question you pose...

First you must ask what kind of car it is... I will assume (for my purposes) that it is actually a minivan with the back seats taken out.  this provides ample testing space.  another question is on the mass of the balloon.  The sources of error could go on and on in this situation, but I will say we are working in a perfect testing environment in which the car is actually a minivan.

Because the balloon is tied to a weight only by string, it has somewhere to go.   Because you simply used the term accelerate, I will give acceleration along the horizontal as my working.

Now, because we are working with a perfect test environment, I can safely say that the balloon will do some pretty predictable stuff.  When accelerating from rest, if you are accelerating at a high enough rate, the balloon will noticeably be drawn backward toward the rear end of the vehicle.  If on the other hand, when you are slowing down suddenly (check def. of acceleration this is correct), the balloon will noticeably be drawn toward the front of the vehicle.  If you are using the weight as your frame of reference, then the balloon is moving in those respective directions; however, if the earth is your frame of reference, then the balloon has gone nowhere forward or backward, but the whole length restriction on the string makes it go down.

I am not a professional scientist, I just like to play around with balloons and physics... I haven't tried this one yet.

Posted by John on 2004-12-17 05:48:28