Sound, Vibrations & Explosions

Beakman’s World turns the volume up this episode as Beakman takes on a viewer’s question about noise and turns it into a hands on tour of sound, before Lester gets dragged into a countdown of things that get bigger, faster. A balloon stretched over a can reveals the hidden shake of a human voice, and a bottle of liquid nitrogen proves that explosions are simply matter changing size in a hurry.

In this episode you will discover:

• Why sound is really just vibrations moving through the air
• How a homemade sound viewer can make your own voice visible
• How a tin can telephone carries a voice along a taut string
• Why air pressure alone can hold water inside an upside down glass
• What actually happens inside an explosion, from popcorn to liquid nitrogen
• How controlled explosions are sometimes used to help rather than harm

The Same Push, Two Speeds

Sound and explosions turn out to be two speeds of the same basic idea. Both are about something pushing on the air, or the water, around it. Sound is a gentle, repeating push, a vibration that travels outward as a wave until it reaches an eardrum and gets read as noise or music. An explosion is the same kind of push taken to an extreme, a substance suddenly getting far bigger than it was a moment before, whether that is steam bursting out of a popcorn kernel or nitrogen gas escaping a warming bottle. Sitting quietly behind both ideas is air pressure itself, the constant, usually invisible push of the atmosphere that Beakman reveals with nothing more than a playing card and a glass of water.

Beakman’s demonstrations

Beakman builds a sound viewer out of nothing fancier than a balloon, a can and a tiny mirror, shining a flashlight off the stretched balloon so the audience can watch his own voice dance across the studio as a moving beam of light. He shows how the same shaking travels through a tightly stretched string in a homemade tin can telephone, then hands things over to Colonel Corn and a squad of safety obsessed helpers for the main event, popping a kernel of corn to show a small explosion before building up to a full sized one, a bottle of liquid nitrogen dropped into a bin of water that sends a geyser of spray flying as the gas inside suddenly expands.

Try this at home

The tin can telephone test. Ask an adult to help remove one end from each of two clean cans and punch a small hole in the closed end of each. Thread a long piece of string through both holes and knot each end so it cannot slip out. Pull the string tight between two people and take turns talking into one can while the other person listens. The voice makes the air in the can vibrate, which vibrates the can, which vibrates the string, which carries the shaking all the way to the other end.

The playing card test. Fill a glass right to the brim with water and cover the top with a playing card, pressing gently so no air is trapped underneath. Holding the card firmly in place, turn the glass upside down over a sink and let go of the card. Air pressure pushing up on the card is stronger than the weight of the water pushing down, so the card, and the water, stay exactly where they are.

The film canister test. With an adult, drop a quarter of a fizzy tablet and a spoonful of water into a small snap lid canister, seal the lid, set it down and step well back. Carbon dioxide builds up inside faster than the sealed canister can hold it, and the lid pops off with a bang, a small, safe version of exactly the same idea behind Beakman’s much bigger liquid nitrogen blast.