Science & TechFact

A whip crack is a sonic boom.

The whip does not crack because it hits something. A wave runs from handle to tip, and because the cord keeps getting thinner, the energy concentrates: the tip breaks the sound barrier. The crack is the shock wave of that tiny supersonic flight. In 2002 physicists worked out how tension and tapering amplify the pulse.

Useful: The same principle is in a towel snap: the loose corner becomes a fast tip.

Source: journals.aps.org

Akustik PhysikUeberschall

Difficulty:

Related cards

Counting seconds tells you how far away the storm is.Sound moves through 20 °C air at about 343 metres per second; light arrives practically instantly. …
Helium doesn't raise your pitch. Seriously.With helium in your lungs, your vocal cords vibrate at exactly the same rate, so the pitch stays …
A kettle is loudest just before it goes quiet.At the bottom the water reaches 100 degrees while the top is still at 70. Steam bubbles form there …
Underwater, sound travels more than four times faster.In air at 20 °C, sound covers 343 metres per second. In fresh water it is 1,481 m/s, in seawater …
Colder than minus 273.15 degrees is impossible.Temperature measures how much particles move. At −273.15 °C, which is 0 kelvin, thermal motion is …
Every banana is slightly radioactive.Bananas are rich in potassium, and about 0.012 % of it is the radioactive isotope potassium-40. One …
No wind turbine can harvest more than 59 percent of the wind.In 1919 Albert Betz showed that a turbine can't stop the air completely, or it would pile up and …
On Everest, water boils at about 70 degrees.Water boils when its vapour pressure matches the air pressure. At sea level that happens at 100 °C. …

Keep reading

This card belongs to the topic Science & Tech. Every card is short, cites a source and can be saved – due ones come back by themselves later.

About Doomlearn · Projects · Legal notice · Privacy · Terms