Twenty science questions across physics, chemistry and biology, each with three answers and the fact that explains the right one. Play them as a quiz, or read the list with the answers marked.
Pick an answer and the fact behind it appears; the next question waits until you are ready. No clock, no sign-up.
Do you know this one?
Tap an answer, or press 1, 2 or 3; Enter for the next question
The same questions as the quiz, right answer highlighted and the fact under it. Print the page for a quiz night: the print layout keeps the questions and answers only. The Science topic in Lock&Learn holds 109 facts in all.
Why is the sky blue instead of violet or red?
Air molecules scatter blue light the most. Sunlight contains every color, but as it passes through the atmosphere, air molecules scatter short, blue wavelengths far more than red or yellow ones, a phenomenon called Rayleigh scattering. Our eyes are also more sensitive to blue than to violet, which scatters even more, so the sky reads as blue rather than violet.
Source: NASA
Why do sunsets glow red and orange instead of blue?
Sunlight crosses far more atmosphere at dusk. When the sun sits low on the horizon, its light travels through a much thicker slice of atmosphere to reach your eyes. Nearly all the blue light gets scattered away along that longer path, leaving mostly the longer red and orange wavelengths to come through.
Source: UCAR Center for Science Education
What creates a shimmering pool of "water" on a sun-baked road that never gets closer?
Hot air near the ground bends light upward. Air right above a heated road is much less dense than the cooler air above it, and light bends as it crosses between those layers. The bent light tricks your brain into seeing a reflection, so the sky appears pooled on the pavement like water that keeps retreating as you approach.
Source: Encyclopaedia Britannica
Why do stars twinkle in the night sky while planets shine steadily?
Stars are pinpoints easily jostled by moving air. A star is so distant that it reaches us as a single point of light, so turbulent pockets of air in the atmosphere bend that point back and forth, producing a twinkle. Planets are close enough to appear as tiny discs, and light from across the disc cancels out the wobble.
Source: UC Riverside Department of Mathematics
Why does a straw look snapped in half the moment it dips into a glass of water?
Light slows and bends where air meets water. Light travels slower in water than in air, so a ray leaving the submerged part of the straw changes direction right at the surface. Your eyes trace that bent path backward in a straight line, making the underwater section appear to jump sideways.
Source: Encyclopaedia Britannica
Why does your voice turn into a squeaky cartoon chirp after inhaling helium?
Helium changes your resonance, not your vocal cords. Your vocal cords keep vibrating at their usual frequency, but sound travels nearly three times faster through light helium gas than through air, changing how your throat and mouth resonate. That shift amplifies the higher tones and mutes the lower ones, giving your voice a thin, squeaky quality.
Source: University of California, Santa Barbara Physics Department
What causes the sudden thunderclap when a jet flies faster than the speed of sound?
A cone-shaped shock wave collapses all at once. A supersonic aircraft shoves air aside so forcefully that the air can't get out of the way in time, piling up into a cone-shaped shock wave trailing the plane. When that wave sweeps past someone on the ground, the abrupt pressure change arrives as a single boom.
Source: NASA
How can you estimate how far away a thunderstorm is without any equipment at all?
Count the seconds between the flash and the boom. Light from a lightning flash reaches your eyes almost instantly, but sound crawls along at roughly one mile every five seconds. Counting the seconds between the flash and the thunder, then dividing by five, gives a rough distance to the strike in miles.
Source: NOAA
Pull a metal spoon and a wooden spoon from the same drawer, which feels colder?
Metal feels colder than wood at the same temperature. What your skin actually senses is how quickly heat is leaving it, not an object's true temperature. Metal conducts heat away from your hand far more efficiently than wood does, so it feels colder even though a thermometer would show them at the exact same reading.
Source: University of Illinois Physics Van
Why does a black car seat get scorching hot in the sun while a white one stays cooler?
Black surfaces absorb nearly all the light that hits them. A white surface reflects most wavelengths of visible light straight back away, leaving little energy behind to turn into heat. A black surface reflects very little, so nearly all the sunlight's energy gets absorbed and converted into warmth instead.
Source: NOAA
What solid turns straight into smoky vapor without ever melting into a puddle first?
Dry ice turns straight from solid to vapor. At normal atmospheric pressure, solid carbon dioxide skips the liquid stage entirely and sublimates directly into gas at about -78.5 degrees Celsius. That's why dry ice appears to vanish into fog instead of leaving behind any wet residue.
Source: Encyclopaedia Britannica
Is there an actual limit to how cold something can ever get?
Absolute zero is the coldest anything can ever get. Absolute zero sits at 0 Kelvin, equal to -273.15 degrees Celsius, the point at which a system's particles hold the least possible energy. Physicists have chilled atoms to within a fraction of a degree of that mark in the lab, but it has never been reached exactly.
Source: NIST
Why can't climbers on Mount Everest brew a proper cup of tea at the summit?
On Everest's summit, water boils at about 70°C. Boiling happens when a liquid's vapor pressure matches the surrounding air pressure, and air pressure atop Everest is only around a third of what it is at sea level. That lets water boil at roughly 70 degrees Celsius instead of 100, never getting hot enough to steep tea the usual way.
Source: CK-12 Foundation
Earth's gravity barely weakens 400 kilometers up, so why do astronauts float aboard the space station?
Astronauts float because they're in constant free fall. At the station's altitude, gravity is still roughly 90 percent as strong as it is on the ground. What looks like weightlessness is really nonstop free fall, since the station moves forward so quickly that it perpetually falls around the curve of the planet instead of straight down.
Source: NASA
What happened when an astronaut dropped two very different objects together on the airless Moon?
A hammer and a feather landed at exactly the same time. With no atmosphere to slow a falling feather down, both objects accelerated at the identical rate during the Apollo 15 demonstration and struck the lunar surface together. On Earth, it's air resistance alone that makes a feather drift down slower than a hammer.
Source: NASA
Why do most coastlines see the ocean rise and fall twice within a single day?
The Moon's pull stretches Earth's oceans into two bulges. The Moon's gravity tugs hardest on the ocean facing it, pulling that water into a bulge, while inertia leaves a second bulge on the exact opposite side of the planet. As Earth spins through both bulges every day, most coasts experience two high tides and two low tides.
Source: NOAA
Who was the first human to break the sound barrier without any engine at all?
A skydiver broke the sound barrier with his own body. Felix Baumgartner jumped from a balloon nearly 39 kilometers above Earth and reached an estimated 1,357.6 kilometers per hour during his fall, becoming the first person to go supersonic using gravity alone. The single jump set eight world records in one afternoon.
Source: Guinness World Records
How does NASA give astronauts a taste of weightlessness without ever leaving the atmosphere?
NASA fakes zero gravity with a plane flying giant arcs. A specially modified aircraft climbs steeply, then dives along a curved path that matches the pull of gravity, putting everyone aboard into free fall for about 25 seconds at a stretch. The plane repeats that arc dozens of times per flight, which is how it earned the nickname "vomit comet."
Source: NASA
Why does ice float instead of sinking to the bottom of your glass?
Frozen water is less dense than liquid water. As water freezes, its molecules lock into an open hexagonal lattice that takes up more space than they occupied as a liquid, making ice about 9 percent less dense. Most substances get denser when they solidify, but water's odd behavior is exactly why icebergs and ice cubes float.
Source: Encyclopaedia Britannica
How do some insects stroll across a pond without ever breaking through the surface?
Water striders stand on water's surface tension. Water molecules cling tightly to one another, creating a taut film known as surface tension. Water striders have long, water-repelling legs that spread their weight across this film, letting them stand and glide on top of the water instead of sinking into it.
Source: USGS
This page has 20, each with three answers and the fact that settles it. They are the first 20 of the 109 facts in the Science topic of Lock&Learn, which holds the rest.
Yes. Read them out, print the page (the right answers are marked) or play the quiz on a shared screen. Each question has one right answer and two plausible wrong ones, and the fact under it gives you something to say after the reveal. Please do not republish the questions elsewhere.
Every fact names its source under the answer, from space agencies and museums to encyclopedias and published research. Lock&Learn writes each one as a teaser question with three answers, and the fact that settles it.
Install Lock&Learn, then touch and hold your Lock Screen, tap Customize, tap the widget area and choose Lock&Learn. A question waits on every screen-wake; you guess, tap, and reveal the verified fact behind the answer. Pick the topics you like and the widget rotates through them.
Yes. Lock&Learn is free on iOS: every topic opens with a free preview and another question unlocks daily. Lock&Learn+ is an optional upgrade that opens every topic in full.