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.

The "floating" of the balloon forward is manifesting the same behavior as different fluids in a spinning centrifuge. For example, uranium gas diffusion centrifuges (found at Portsmouth OH, Oak Ridge TN, and Paducah KY) routinely separate fissile U-235 from U-238. Granted these accelerations are much higher, but the density difference (0.5%) between the two gases is much lower than the density difference between helium in a balloon and air (83.6%).

Posted by Steven Lord on 2020-12-09 20:31:31