lew@sri-unix (08/16/82)
Having received two requests for explanation of the Helium-balloon- in-the-accelerating-car effect, I'm posting this. The air in the car sloshes to the back, pushing the balloon to the front. It behaves like a bubble in a sealed bottle of water. More abstractly, in the car frame of reference, the fictitious force which pushes you into your seat adds to the force of gravity (vectorially), creating a force field slanting down and to the back. A Helium balloon, being buoyant, anti-aligns with this force field (assuming it is tethered.) Lew Mammel, Jr. - BTL Indian Hill