Science Riddles

Because they make up everything. Fact: your body contains roughly 7 octillion atoms, and most of them are hydrogen.

Wordplay on make up, since atoms compose all matter while also meaning to invent falsehoods.

The Sun. Fact: sunlight takes about 8 minutes and 20 seconds to reach Earth.

The Sun radiates heat across 93 million miles and powers photosynthesis that lets plants grow.

Steam. Fact: water expands about 1,600 times in volume when it turns to steam.

Steam is water vapor, less dense than liquid water, so it rises while boiling water stays below.

Mercury. Fact: it's so dense that a cannonball can float on it.

Mercury is the only metal liquid at room temperature and shares its name with the planet.

Refraction, the bending of light. Fact: rainbows appear because raindrops bend and split sunlight.

Refraction bends light through glass and water and splits white light into its spectrum of colors.

A neutron star. Fact: some spin hundreds of times per second.

A neutron star is a collapsed stellar core packed so densely that a spoonful weighs billions of tons.

Fog. Fact: fog is just a cloud that touches the ground.

Fog is a ground-level cloud of water droplets that scatters light and reduces visibility.

A tree. Fact: one large tree can absorb around 48 pounds of carbon dioxide a year.

Wordplay on a tree's bark and growth rings while it absorbs the carbon dioxide people exhale.

Lightning. Fact: light travels about 900,000 times faster than sound, so the flash always beats the thunder.

Lightning's flash reaches you almost instantly while its thunder lags because light far outpaces sound.

The mitochondrion. Fact: mitochondria have their own DNA, separate from the cell's nucleus.

Mitochondria make the cell's energy, the classic biology-class line about the powerhouse of the cell.

Water. Fact: the human body is about 60 percent water.

Water exists as solid, liquid, and gas, covers most of Earth, and makes up much of the body.

Air. Fact: air is about 78 percent nitrogen, not mostly oxygen as many people guess.

Air is an invisible gas you breathe that resists compression and expands when heated.

Gravity. Fact: gravity on the Moon is about one sixth of Earth's, which is why astronauts bounce.

Gravity pulls you down as you stand yet also keeps you anchored to the planet.

Mars. Fact: Mars hosts Olympus Mons, the tallest volcano in the solar system, about two and a half times the height of Everest.

Mars is the reddish fourth planet named for the Roman war god and visited by rovers.

The lens of your eye. Fact: your eye's lens keeps changing shape all day to focus near and far.

The eye's lens changes shape to bend incoming light and focus a sharp image on the retina.

A comet. Fact: a comet's tail always points away from the Sun, pushed by solar wind.

A comet is an icy body that grows a tail pointing away from the Sun as it warms.

A diamond. Fact: both diamond and graphite are pure carbon, just with different atomic arrangements.

Diamond is the hardest natural material, made of carbon just like the graphite in pencil lead.

Sound needs a medium like air to travel, and space is a near-perfect vacuum. Fact: astronauts' radios convert sound to radio waves, which travel fine in a vacuum.

Sound waves need a medium to travel, and space is a vacuum with no air to carry them.

A dinosaur. Fact: birds are living dinosaurs, descended from small feathered theropods.

Dinosaurs ruled for over 160 million years, and modern birds are their living descendants.

Your heart. Fact: in an average lifetime the heart beats more than 2.5 billion times.

The heart is a fist-sized muscle that beats constantly to pump blood through the body.

Iron. Fact: the iron in your blood was literally created by ancient stars.

Iron is magnetic, gives blood its red color through hemoglobin, and forms inside dying stars.

Static electricity (electric charge). Fact: like charges repel, which is why charged hair strands push apart and stand up.

Static electricity builds like charges that repel, so a charged balloon makes hair strands push apart.

A spider. Fact: by weight, spider silk is about five times stronger than steel.

Spider silk is remarkably strong for its weight, and spiders have eight legs.

Pi. Fact: pi has been computed to over 100 trillion digits, and its decimals never repeat.

Pi is the endless non-repeating ratio of a circle's circumference to its diameter.

A lake (or any body of water). Fact: ice floats because water is one of the few substances less dense as a solid than as a liquid.

Water freezes at the surface first because ice is less dense than liquid water and floats.

Hormones. Fact: adrenaline can make your heart rate jump within seconds of a scare.

Hormones are chemical signals sent through the blood by glands, including adrenaline.

Light. Fact: light travels at about 299,792 kilometers per second in a vacuum.

Light is the fastest thing in the universe and reaches your eyes for you to see.

A volcano. Fact: the Hawaiian islands were built entirely by volcanic eruptions over millions of years.

A volcano is a mountain that erupts lava, and repeated eruptions can build whole islands.

Carbon dioxide

Plants take in the carbon dioxide that animals breathe out, driving photosynthesis.

The Sun

The Sun is by far the closest star to Earth at about 93 million miles away.

Starfish (star + fish). Biology bonus: a starfish has no brain and no blood, yet it can regrow an arm it loses to a predator.

Emoji rebus combining star and fish makes starfish, the tide-pool sea creature.

Firefly (fire + fly). Nature bonus: its glow comes from a chemical reaction called bioluminescence, which gives off light with almost no heat.

Emoji rebus combining fire and fly makes firefly, the beetle that glows by bioluminescence.

A black hole.

A black hole's gravity is so strong that not even light can escape past its edge.

A magnet.

A magnet's like poles repel, so pushing two north ends together makes them shove apart.

DNA.

DNA is the twisted double-helix molecule in cells that stores genetic instructions.

Saturn.

Saturn is the ringed planet whose bright rings are made of ice and rock particles.

Chlorophyll.

Chlorophyll makes leaves green and captures sunlight to power photosynthesis.

A bat.

Bats navigate in darkness using echolocation, reading echoes of their own calls.

Salt.

Table salt forms from reactive sodium metal and poisonous chlorine gas bonded together.

A snowflake.

Snowflakes grow six-sided from ice crystal geometry, each one uniquely shaped.

Helium.

Helium is the second lightest element and lifts balloons while raising voice pitch.

A tornado.

A tornado is a violent spinning funnel of air stretching from storm cloud to ground.

A compass.

A compass needle aligns with Earth's magnetic field but nearby magnets throw it off.

The Milky Way.

The Milky Way is the spiral galaxy of hundreds of billions of stars that holds our Sun.

A battery.

A battery stores chemical energy and converts it to electricity when a circuit connects.

An electron.

Electrons are the negatively charged particles orbiting an atom, and their flow is current.

A tardigrade.

Tardigrades are microscopic animals that endure extreme heat, cold, and the vacuum of space.

A fossil.

A fossil is stone that preserves the shape of an organism from millions of years ago.

The Moon

The Moon produces no light itself and shines only by reflecting sunlight toward Earth.

Oxygen

Oxygen is the gas animals breathe in and that plants release during photosynthesis.

Inertia

Inertia is an object's resistance to any change in motion, so your body keeps moving when the car halts.

Density

Whether an object floats depends on its density compared to water, not its size or weight alone.

Absolute zero

Absolute zero is the lowest possible temperature, about minus 273 Celsius, where atomic motion almost stops.

A half-life

A radioactive isotope's half-life is the constant time for half its atoms to decay, regardless of sample size.

Plasma

Plasma is the fourth state of matter, superheated ionized gas that forms stars and most visible matter.

Sublimation

Sublimation is when a solid turns directly into gas without passing through a liquid phase.

Antimatter

Antimatter mirrors normal matter and annihilates into energy the instant it meets its counterpart.

Dark matter

Dark matter is invisible mass detected only through the gravitational pull it exerts on galaxies.

Nuclear fusion

Nuclear fusion merges hydrogen nuclei into helium, releasing the energy that makes stars shine.

A superconductor

A superconductor carries electricity with no resistance once cooled below its critical temperature.

An enzyme

Enzymes are biological catalysts that accelerate reactions without being used up in the process.

A virus

A virus is a non-living particle that can replicate only by taking over a living host cell's machinery.

A neuron

Neurons are nerve cells that pass information as electrical signals through the brain and body.

An octopus

An octopus has three hearts, copper-based blue blood, and taste receptors along its arms.

An axolotl

The axolotl is a salamander famous for regrowing limbs, organs, and even parts of its brain.

The immortal jellyfish

The immortal jellyfish can revert its adult cells back to a juvenile polyp stage, effectively restarting its life.

An electric eel

The electric eel is actually a knifefish that generates powerful shocks to stun prey and defend itself.

Rust

Rust forms when iron reacts with oxygen and moisture, a slow oxidation that weakens the metal.

Ozone

Ozone is a molecule of three oxygen atoms that shields Earth by absorbing ultraviolet radiation.

The aurora

Auroras glow when charged solar particles collide with gases high in the atmosphere near the poles.

A solar eclipse

A solar eclipse happens when the Moon passes directly between Earth and the Sun, blocking its light.

The tides

Tides are the daily rise and fall of the sea caused mainly by the Moon's gravitational pull.