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.

Regarding nikki's scuba idea, a large container of water being driven around in a huge vehicle, with a human underwater...

Most humans with a lung full of air are less dense than water, called "positive buoyancy", and float up.  A thin person who empties their lungs as much as possible, would likely sink in fresh water.  An obese person might float even after a full exhalation, since fat is less dense than water.  Salt water is more dense than fresh water, so everyone floats higher in salt water than fresh water.

But a SCUBA diver wears a jacket with air bladders, called a BCD (buoancy control device).  Air can be added or subtracted from the BCD to adjust the diver's buoyancy.  So nikki's experiment could be done by having the scuba diver tethered to the bottom, inflate the BCD, and you have the same situation as the helium balloon in the car.  Only problem would be if the rope breaks and the diver surfaces too fast.... ouch!

Posted by Larry on 2004-12-17 14:34:19