Dear Tom and Ray:

The other day my kids had a helium-filled balloon in the car. Whenever I stepped on the brakes, all the passengers were pushed forward, but the helium filled balloon went backwards. Why is this? -- Jeff

Tom: Great question, Jeff. I guess this was one of those laws of physics that Newton never got around to writing.

Ray: The reason the helium-filled balloon goes backwards when you step on the brakes is because everything else in the car -- including the air -- goes forward.

Tom: According to our buddy Isaac Newton, when your car is in motion and you step on the brakes, your passengers and the air around them "remain in motion" -- that is, they go forward. And when the air "goes forward," it pushes the helium (which is lighter than air) out of the way, or toward the back of the car.

Ray: It's the same reason we say "hot air rises." Hot air doesn't actually "rise." Cold air sinks! Cold air is heavier, so it drops down toward the floor and displaces the warmer, lighter air, which gets pushed up to the ceiling.

Tom: The more interesting question, Jeff, is what happens when you suck in the helium, and then -- in a helium-induced Mickey Mouse voice -- ask an unsuspecting toll-taker to "take me to your leader, earthling."

Changing your oil is the cheapest insurance you can buy for your car, but how often should you change it? Find out by ordering Tom and Ray's pamphlet Ten Ways You May Be Ruining Your Car Without Even Knowing It! To order, send (check or money order) to Ruin, P.O. Box 536475, Orlando, FL 32853-6475. You can also order online.

© 1996 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

Back to the May 1996 index