Geography & Places · Video 1:19
Why Is the Dead Sea So Salty?
The Dead Sea is so salty because water leaves only by evaporation, leaving the salt behind. See how salty it is, why people float and why its level is falling.
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Short videos and clear, sourced articles that explain how the world works, one question at a time.
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Health & Body
Why Do We Yawn?
Why do we yawn? See what happens in a yawn, why the oxygen idea failed, what brain-cooling studies found and what research says about contagious yawning.
People
Who Was Albert Einstein?
Albert Einstein's 1905 papers and general relativity made him famous. Why his Nobel Prize cited the photoelectric effect, and his 1939 letter to Roosevelt.
Arts & Culture
Why Did Van Gogh Cut Off His Ear?
Van Gogh cut off his left ear in Arles on 23 December 1888 during a mental breakdown after a row with Gauguin. What is known about it, and what remains unclear.
Food & Drink
Why Do Onions Make You Cry?
Cutting an onion lets two enzymes make syn-propanethial-S-oxide, a gas that stings eye nerves. Learn the chemistry, tearless onions and why sharp knives help.
Language & Words
Where Does the Word Robot Come From?
Robot first appeared in Karel Čapek's 1920 play R.U.R. His brother Josef suggested it, from the Czech robota, forced labour. See how it reached English.
Ideas & Beliefs
Who Were the Twelve Olympian Gods?
The twelve Olympians were the chief gods of ancient Greek religion. See who they were, what each was god of, their Roman names and how Greeks worshipped them.
Sports
Why Is Tennis Scored 15, 30, 40?
Tennis counts love, 15, 30, 40 and game, with deuce at 40-all. See how games, sets and tie-breaks work, and why nobody knows where the odd numbers came from.
Society & Government
What Does the United Nations Do?
What the United Nations does: why it was founded in 1945, how its six main organs and the Security Council veto work, plus its peacekeeping, aid and funding.
History & Places
People
Who Was Ada Lovelace?
Ada Lovelace, Lord Byron's daughter, wrote the 1843 Notes on Babbage's Analytical Engine, including what is often called the first computer program.
History
Who Built the Pyramids of Giza?
The Giza pyramids were built for kings Khufu, Khafre and Menkaure. A workers' town and tombs point to organized, well-fed Egyptian crews rather than slaves.
Geography & Places
What Is the Tallest Mountain in the World?
Everest is the highest mountain above sea level at 8,848.86 m, but Mauna Kea is taller from base to peak and Chimborazo's top is farthest from Earth's centre.
History
How Long Is the Great Wall of China?
The Great Wall of China is 21,196.18 km long, according to China's official survey of walls from all periods. The Ming dynasty wall alone is 8,851.8 km.
Science & Nature
Earth & Environment
What Causes Earthquakes?
Earthquakes happen when stress stored along a fault is released as sudden slip, sending out seismic waves. How faults work, magnitude, and where quakes strike.
Nature & Animals
Why Do Cats Purr?
Cats purr as their vocal folds vibrate at about 25 to 150 Hz. They purr when content but also when stressed or hurt, and some hide a cry in the purr to get fed.
Health & Body
Why Do We Need Sleep?
Why do we need sleep? Learn the stages of sleep, how it helps memory and the body, the debate over brain cleaning, and how much sleep experts recommend.
Space
How Hot Is the Sun?
NASA puts the Sun's core at about 15 million °C and its surface at 5,500 °C, yet its outer corona reaches 2 million °C. Here is why, and how the heat is made.
Technology
Technology
How Does Wi-Fi Work?
Wi-Fi links devices to a router by radio on the 2.4, 5 and 6 GHz bands. See how the bands trade range for speed, what Wi-Fi 4 to 7 mean and how WPA3 works.
Transportation
How Does a Car Engine Work?
A car engine burns fuel inside its cylinders. See how the four strokes work, how pistons turn the crankshaft, how diesels differ, and where the energy goes.
Technology
How Do Touchscreens Work?
Resistive touchscreens sense two layers pressed together; capacitive ones sense a finger's effect on an electric field. How each works, and why gloves fail.
Transportation
How Do Electric Cars Work?
Electric cars run on a traction battery that powers an electric motor. How the main parts work, regenerative braking, hybrids, charging levels and efficiency.
Society
Language & Words
Where Did the Alphabet Come From?
The alphabet began about 4,000 years ago, when Semitic speakers reworked Egyptian hieroglyphs. Follow it through the Phoenicians, Greeks and Romans to English.
Ideas & Beliefs
What Is Utilitarianism?
Utilitarianism judges actions by their consequences for overall happiness. Learn Bentham's calculus, Mill's higher pleasures, act vs rule views and objections.
Business & Economy
How Does Netflix Make Money?
Netflix earns almost all its revenue from monthly membership fees, with ads a small but growing extra. Here are its 2025 results by region and its biggest cost.
Society & Government
How Does a Bill Become a Law in the U.S.?
How a U.S. bill becomes law: introduction, committee work, House and Senate votes, the filibuster and cloture, and the President's signature, veto or override.
Culture & Leisure
Entertainment
Why Do Movies Play at 24 Frames per Second?
Movies run at 24 frames per second because early sound films needed one fixed, faster speed. See how the standard arose and why TV and HFR films differ.
Arts & Culture
Who Painted the Sistine Chapel Ceiling?
Michelangelo painted the Sistine Chapel ceiling in fresco for Pope Julius II from 1508 to 1512, with nine Genesis scenes and prophets and sibyls around them.
Food & Drink
Where Does Coffee Come From?
Coffee beans are the seeds of the coffee cherry. See how arabica and robusta differ, how coffee spread from Ethiopia and Yemen, and where it is grown today.
Sports
How Does the Offside Rule Work in Soccer?
Under Law 11, being in an offside position is not an offence until a player joins in play. See what counts, when offside can't happen and how VAR checks it.
Daily Life
Everyday Life
Why Are There Seven Days in a Week?
No natural cycle sets the week. Seven days came from Babylonian, Jewish and Roman traditions and seven visible planets, and survived French and Soviet reforms.
Everyday Life
Why Do We Have Daylight Saving Time?
Daylight saving time moves clocks ahead one hour to shift daylight to the evening. Learn where it began, how U.S. law works and whether it saves energy.
Everyday Life
Why Do We Have Leap Years?
Leap years add February 29 because Earth's orbit takes about 365.2422 days. See how the four-year rule and the century exception keep the seasons in place.
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