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We answered! Experts reveal the shocking truth behind the mysteries of science

Why does my voice sound funny after I suck on a helium balloon?

Luis Zambrano, 12 Maracay, Venezuela

You've probably noticed how helium balloons float, while the ones you blow up fall to the floor. That's because helium, a gas, is seven times lighter than the air you puff into a balloon. This difference in air density (mass of molecules in a given space) makes you squeak like a cartoon character, explains Kenneth Stevens, a professor of electrical engineering at Massachusetts Institute of Technology--he studies how humans produce and perceive speech sounds.

Sounds are really waves that move in air. When you speak, sound waves form from air traveling through the larynx (voice box), vibrating at the vocal cords (small muscular folds), and then resonating (echoing) in the vocal tract (mouth, cheeks, tongue, teeth, and lips). Since helium is lighter than regular air, it vibrates faster, creating faster-moving sound waves. The velocity (speed) at which a sound wave travels determines its frequency (pitch). The quicker the waves move in the vocal tract, the higher the pitch you hear.

Sounding like Mickey Mouse may give your pals a good laugh, but inhaling heavy doses of pure helium (found in balloon tanks) is dangerous. "When we do experiments, we use a helium-oxygen mixture," Stevens says, because if you don't get enough oxygen, you can pass out, damage your lungs, or even die! That's nothing to squeak at.

How come leg hair grows faster than head hair?

Jessica Whalen, 12 Des Plaines, Illinois 

One reason leg hair appears to grow faster than head hair is because it's easier to spot hair sprouting on bare or shaven skin than on a full head of hair. "If you shaved your head, you'd probably notice the growth too," says Michael Holick, professor of medicine and dermatology (skin science) at Boston University Medical Center.

Basically, your age, gender, race, health, environment, and genes (traits you inherit from your parents) play a big role in determining how fast hair grows on your different body parts. So everyone's different!

The 5 million hair follicles (bunches of skin cells that make hair) on your body and scalp (about 100,000 on your scalp alone) go through cycles of growth, rest and re-growth.

On average, head hair grows between 1.5 and 3 centimeters (0.5 to 1 inch) per month and can grow from two to six years before it stops growing and falls out (don't worry, it starts again).

The growth cycle for leg hair isn't as long (19 to 26 weeks). "In fact they cycle faster," says Holick, offering another reason for what seems like speedier growth. "If not, you'd see two feet of hair streaming down your legs," adds Holick. Aren't you glad that doesn't happen?!