Science Questions to Ask

Why ask it

Sunlight is a mix of every color, and the gas molecules in air scatter the blue end of it far more strongly than the red, so blue arrives at your eye from all over the sky. At sunset the light crosses much more air, most of the blue has been scattered out of the beam, and orange and red are what is left. Anyone who says the sky reflects the ocean has it backward.

Why ask it

Most solids sink in their own liquid. Water is the odd one: as it freezes its molecules lock into an open pattern that takes up more room, so a block of ice is slightly less dense than the water around it. Ask what a pond would be like in winter if ice sank, and the answer leads straight to how fish survive under the surface.

Why ask it

The tilt of the Earth's axis, which leaves each half of the planet leaning toward the Sun for part of the year and away from it for the rest. The common wrong answer is distance. Two facts dispose of it: the northern and southern hemispheres have opposite seasons, and the Earth is closest to the Sun in early January.

Why ask it

Half of the Moon is always lit by the Sun, and as it circles the Earth we see more or less of that lit half. The usual mistake is to say the Earth's shadow covers part of it, which describes a lunar eclipse instead. A ball held at arm's length in a room with one lamp settles it in a minute.

Why ask it

Sunlight bends as it enters a raindrop, reflects off the back of the drop and bends again on the way out, and each color bends by a slightly different amount, which spreads white light into a band. A complete answer adds that the Sun is always behind you, and that the bow is curved because each color comes back at its own fixed angle from the point opposite the Sun.

Why ask it

Rivers are not quite fresh. They carry small amounts of minerals dissolved out of rock, and when seawater evaporates the water leaves and the salts stay behind, so over a very long time they have built up. If the reply is that the sea simply started out salty, ask what happens to a lake that has rivers running in and none running out.

Why ask it

Inside a storm cloud, colliding bits of ice separate electric charge until it jumps as a giant spark, and thunder is the sound of the air along that path heating and expanding almost instantly. The flash reaches you at once and the sound takes roughly five seconds a mile, so counting the gap tells a child how far off the storm is. Exactly how the charge builds up is still being worked out, and a good answer admits it.

Why ask it

Shoes rubbing on carpet pick up extra electrons, and the charge sits on your body with nowhere to go until your hand nears metal, when it jumps the last gap as a small spark. It happens more on dry winter days because damp air lets the charge leak away unnoticed. This is lightning at a size that fits in a hallway, a link worth drawing for a child who has just asked about storms.

Why ask it

Both are at room temperature, and a thermometer would say so. Metal carries heat away from your fingers quickly and wood does not, and skin reports how fast it is losing heat, not the temperature of the thing it touches. When someone insists the metal really is colder, hand them the thermometer.

Why ask it

A soap molecule has one end that is drawn to water and one end that is drawn to oil. The oily ends bury themselves in the grease and the watery ends face outward, so the grease breaks into tiny coated droplets that rinse away. A reply that stops at soap killing germs has skipped the question of why water alone leaves your hands greasy.

Why ask it

Light changes speed when it passes from water into air, and that change turns its path at the surface. Your brain assumes light has come in a straight line, so it places the underwater part of the straw where it is not. Extend it to a swimming pool, which looks shallower than it is for the same reason.

Why ask it

Gravity is the pull every mass has on every other, strong enough to notice only when one of them is the size of a planet. A heavier ball is pulled harder but is also harder to get moving, and the two effects cancel exactly, so both speed up at the same rate. A feather lags because of the air, which is the detail a careful answer mentions without being asked.

Why ask it

Gravity at that height is only a little weaker than on the ground, so 'there is no gravity in space' is the answer to correct. The station and everyone in it are falling around the Earth together, moving sideways so fast that they keep missing it. The moment at the top of a trampoline bounce, stretched out for months, is a fair way to put it to a child.

Why ask it

Energy is hard to define in one line, and an honest reply says so before describing it as a quantity that changes form while its total stays the same. The ball's motion has not vanished: friction turned it into a slight warming of the ball, the floor and the air. Listen for 'used up' or 'lost', which are the words that need a follow-up.

Why ask it

Temperature measures how fast the particles in something are jiggling on average, and heat is energy moving from a hotter thing to a colder one. A spark from a sparkler is far hotter than a bath, yet the bath holds vastly more energy, which is why one stings for an instant and the other warms you through. If the two words are being swapped freely, that pair of examples sorts it out.

Why ask it

Electrons, which were in the wire all along and creep through it far more slowly than you walk; in household wiring they mostly shuffle back and forth in place. The light comes on at once because the push travels around the whole circuit at close to the speed of light, the way water leaves a hose that is already full the moment the faucet opens. A battery or a socket that 'pours electricity into an empty wire' is the picture to correct.

Why ask it

The belief to test is that magnets pull on all metals, and a fridge magnet held to a soda can or a strip of kitchen foil ends it. Every electron acts as a tiny magnet; in most materials they point every which way and cancel, while in iron, nickel and cobalt neighboring atoms line up together in patches. Why those few do it comes down to quantum mechanics, and a teacher who says so is being straight with you.

Why ask it

Neither picture is enough alone. Light spreads, bends around edges and overlaps with itself the way waves do, yet it is always absorbed in whole packets called photons, and the same turns out to be true of electrons. Be cautious of a reply that picks one side, or that has light switching back and forth between the two.

Why ask it

The closer anything with mass gets to light speed, the more energy each extra bit of speed costs, and reaching it would take an unlimited amount. The limit is built into how space and time are connected, so it is not an engineering problem waiting for a better engine. Follow up with what happens to time for a fast traveler, since the clocks on navigation satellites have to be corrected for it.

Why ask it

Sound is a vibration handed from one particle to the next, so it needs something to travel through: air, water, a wall, a steel rail. It moves faster through water than through air and faster still through steel, which surprises people who expect solids to block it. Space has almost nothing between its particles to pass the vibration on, whatever movie explosions suggest.

Why ask it

While it approaches, each sound wave starts a little closer to you than the last, so the waves arrive bunched together and the note is higher; once it has passed they arrive stretched out and the note is lower. The siren itself never changes. A similar stretching in the light of distant galaxies is how astronomers learned the universe is expanding, which makes this a bridge from the street to space.

Why ask it

The wing is tilted and shaped so that it turns the passing air downward, and the air pushes back up on the wing. Many books say air over the curved top has to speed up to rejoin the air underneath, and that part is wrong: nothing makes the two streams meet again. Ask how a plane can fly upside down, which the downward-turned air handles and the other story cannot.

Why ask it

What matters is the whole shape, not the material. A hull encloses a great deal of air, so the ship taken as one object is less dense than water, and it settles until it has pushed aside water weighing as much as itself. A lump of modeling clay that sinks, then floats once it is pressed into a bowl, makes the point without any equations.

Why ask it

A tiny, dense nucleus of protons and neutrons holds nearly all the mass, with electrons occupying the much larger region around it. The drawing of electrons circling like planets is a sketch and not a portrait, since an electron is better described as a cloud of places it might be found. 'Mostly empty' is fair as a first answer, and a careful teacher adds that those clouds pushing on each other are why your hand does not pass through the table.

Why ask it

An element is one kind of atom, a compound is two or more kinds bonded in a fixed ratio, and a mixture is substances sharing a container without bonding. The sign of real understanding is knowing that a compound behaves nothing like its ingredients: a reactive metal and a poisonous gas make table salt. Try the sorting game with gold, water, air and salt water.

Why ask it

Elements run in order of their number of protons, and each column gathers elements whose outer electrons are arranged alike, which is why they react alike. The story that makes it stick is that Mendeleev left gaps in his table and described elements nobody had found yet, and they later turned up much as described. An answer that treats the table as a list to memorize has missed that it makes predictions.

Why ask it

They change partners: bonds break, new ones form, and the substances at the end have different properties from the ones at the start. No atom is made or destroyed along the way, so the total mass stays put. Test that with a burned log, whose missing weight left as carbon dioxide and water vapor, and contrast it with melting ice, where nothing new was made.

Why ask it

Fire is not a substance. It is a fast reaction between a fuel and oxygen that gives off heat and light, and a flame is the glowing hot gas and soot where that reaction is under way. Fuel, oxygen and heat all have to be present, so asking why a candle goes out under a glass, or why blowing can either kill a flame or feed one, checks the idea.

Why ask it

Water as a gas. Many students say air, or hydrogen and oxygen, but boiling does not break water molecules apart, it only frees them from one another. Credit anyone who points out that the tiny bubbles clinging to the pan before the boil are dissolved air, then ask why the water stops getting hotter once it is boiling.

Why ask it

A water molecule is slightly positive at one end and slightly negative at the other, so water can tug the charged particles of a salt crystal apart and surround them. Oil molecules offer no charged regions for water to hold, and the water molecules cling to one another and squeeze the oil out. If a child says the salt has disappeared or melted, let a saucer of salt water dry out and look at what is left.

Why ask it

In water an acid gives up hydrogen ions and a base takes them up, and the pH scale counts how many are loose, with each step a tenfold change. Two beliefs need unpicking: that every acid is dangerous, when lemon juice and vinegar are acids, and that bases are the gentle ones, when strong bases are as harsh as strong acids. Red cabbage juice changes color in lemon juice and in baking soda water, which makes the scale visible.

Why ask it

Rusting is iron reacting slowly with oxygen where water is present, and the flaky product falls away and exposes fresh metal to the same fate. Gold barely reacts with anything in air, which is also why it turns up in the ground as metal. A nice extension is aluminum, which is more reactive than iron but seals itself under a thin, tough layer of its own oxide.

Why ask it

Some nuclei hold an unstable mix of protons and neutrons and settle down by throwing out particles or energy, often turning into a different element as they do. A half-life is the time it takes for half of any sample to change, whether that is a fraction of a second or billions of years. Common slips are the green glow of cartoons and the idea that nothing is left after two half-lives, when a quarter is.

Why ask it

About four and a half billion years. The figure matters less than the method: certain radioactive atoms in rock change into other atoms at a steady, measured pace, so the ratio between the two works as a clock, read in meteorites and in the oldest minerals found on Earth. If only the number comes back, ask how it was measured.

Why ask it

The Earth's outer shell is broken into plates that move about as fast as fingernails grow, and most earthquakes and volcanoes sit along the edges where plates collide, separate or grind past each other. Check the picture of what lies beneath: the mantle is hot solid rock that creeps, not a sea of lava with continents floating on it. A map of recent earthquakes traces the plate edges so neatly that it does half the explaining.

Why ask it

Water evaporates, mostly from the oceans, rises and cools, and condenses onto specks of dust or salt as droplets, which fall once enough of them have merged. A cloud is liquid droplets or ice crystals, not vapor, and it is not weightless: its droplets are so small that they sink very slowly while rising air holds them up. Ask where the water was a week ago to get the whole cycle instead of its last step.

Why ask it

Weather is what the sky is doing today, and climate is the pattern of weather in a place over decades. The mix-up shows when one cold week is offered as evidence against a warming planet, or one hot afternoon as evidence for it. To make it concrete, ask how many years of records a class would want before calling their own town's winters milder, and why one year would not do.

Why ask it

Sunlight warms the ground, the ground gives that energy back as infrared, and gases such as carbon dioxide, water vapor and methane absorb some of it and send part back down. Without any of this the planet would be frozen, so the effect itself is natural and the concern is about strengthening it. The most common muddle is with the hole in the ozone layer, which is a separate problem with a separate cause.

Why ask it

The Moon pulls harder on the side of the Earth facing it than on the far side, and that difference stretches the oceans into two bulges that the planet turns through each day. Explaining the bulge on the far side is the real test, since 'the Moon pulls the water toward it' accounts for only one high tide. The Sun adds a smaller stretch of its own, which is why the range swells and shrinks through the month.

Why ask it

The Moon turns once on its axis in the time it takes to go once around the Earth, so the same side stays toward us. It did not start that way: the Earth's pull slowed its spin until the two matched. Listen for two slips, that the Moon does not rotate at all and that the far side is permanently dark, when it gets as much daylight as the side we see.

Why ask it

A star is a huge ball of hot gas held together by its own gravity, and in its core hydrogen nuclei are squeezed together into helium, releasing energy. That is fusion, not burning: no oxygen is involved, and a fire the size of the Sun would have gone out long ago. For younger children the surprise is simpler, that the Sun is a star and the other stars are suns too far away to feel.

Why ask it

Gravity pulls everything toward the center, and once an object is massive enough that pull overcomes the strength of rock and drags it into the one shape with no high corners, a ball. Small bodies lack the gravity to do it, so they keep whatever shape collisions left them. Planets are not perfect spheres either, because spin makes them bulge a little at the equator.

Why ask it

Nothing about Pluto changed. In 2006 astronomers agreed on a definition with three tests, orbiting the Sun, being round and having cleared its path of other bodies, and Pluto, which shares its region with many icy objects, fails the third. It is a lesson in how classification works: people draw the lines, and some astronomers still argue with this one.

Why ask it

A region where so much mass is packed so tightly that inside a certain boundary nothing, light included, can get back out. The largest stars leave one behind when they collapse. The picture to correct is the cosmic vacuum cleaner: from a distance a black hole pulls no harder than a star of the same mass, and what happens at its very center is not understood.

Why ask it

That the universe was once extremely hot and dense and has been expanding and cooling for close to fourteen billion years. It was not an explosion at one spot into empty space, because space itself is what stretches, and the evidence includes the retreat of distant galaxies and a faint glow of leftover heat arriving from every direction. What came before, and whether 'before' means anything there, nobody knows.

Why ask it

No sign of it has been found, and a straight answer starts there. The search goes after liquid water, under the ice of some moons and in the past of Mars, and after gases in the air of distant planets that are hard to explain without something alive. If the reply jumps to radio signals and visitors, bring it back to microbes, which is where much of the looking is aimed.

Why ask it

Most people say the soil, and it is mostly air. A tree builds its body from carbon dioxide taken in through its leaves and water drawn up through its roots, with sunlight for energy and only a small share of minerals from the ground. A Flemish experimenter in the 1600s grew a willow in a weighed tub for five years and found the soil had lost almost nothing.

Why ask it

DNA is a very long molecule, coiled inside nearly every cell of the body, whose four chemical letters spell out instructions for making proteins. A child gets half of the set from each parent, so both sets of instructions are at work in the same body. When the reply talks about 'a gene for' height or cleverness, slow it down: most traits depend on many genes acting together and on how a person grows up.

Why ask it

The leading explanation is an asteroid strike about 66 million years ago, its crater buried at the edge of Mexico's Yucatan Peninsula, at a time when huge volcanic eruptions in what is now India may have added to the damage. The second half has a firm answer that delights most classes: birds descend from one branch of the dinosaurs, so a pigeon is a living one. Careful replies keep the confident part and the debated part separate.

Why ask it

Gills take up oxygen gas that is dissolved in the water, the same oxygen that is in air. The mistake to listen for is that fish pull the O out of H2O, which they do not, and it is why an aquarium needs air bubbled through it. Our lungs fail underwater for a plain reason: water holds far less oxygen than air and is much too heavy to move in and out fast enough.

Why ask it

Working muscles use oxygen and fuel many times faster than resting ones, and the heart is the pump that delivers both and carries off the carbon dioxide, so it has to move more blood each minute. The nervous system raises the rate as soon as you set off, and often a moment before, ahead of any change in the blood. Counting a pulse for fifteen seconds before and after a minute of jumping jacks turns the answer into a measurement.

Why ask it

No. Scans show activity throughout the brain over the course of a day, different regions do different jobs, and damage to almost any part has some effect. It earns its place because so many people have heard the claim, which lets a class practice asking where a 'fact' came from and what evidence would support it.

Why ask it

Nobody has a settled answer, and that is the reason to ask. Ideas include cooling the brain and shifting the body between drowsy and alert, while the old explanation about needing more oxygen has not held up well when tested. It shows a child that 'we do not know yet' is a real scientific answer, even about something our own bodies do every day.

Why ask it

It senses gravity. In the tip of a root, dense starch grains settle to the low side of certain cells, and that shifts where a growth hormone collects, so the root bends down and the shoot bends up, with light taking over once the shoot is above ground. A bean sprouted against the side of a glass jar, then laid on its side for a few days, shows the correction happening.

Why ask it

The limit is the point, because it forces out the essentials: living things vary, some of that variation is inherited, and the variants that leave more offspring become more common over generations. Check two things in whatever comes back. It should be about populations and not one animal changing during its life, and nothing in it should 'try', 'want' or 'need' to change.

Why ask it

It can be settled, at least in principle, by looking: some observation or measurement could show a proposed answer to be wrong. 'Which ice cream is best' cannot be tested, and 'which ice cream melts fastest' can. Use it to help a child rework a big why into something with a measurement in it, which is most of the work of a science project.

Why ask it

The classroom version runs question, hypothesis, experiment, results, conclusion, and it is a fair summary of the logic. Real work loops back, starts in the middle, and in fields such as astronomy and geology leans on careful observation where no experiment is possible. Reciting the steps is fine for a test, and saying how untidy it gets is closer to the truth.

Why ask it

A hypothesis is a proposed answer you can test. A law describes a regular pattern, often as an equation, and a theory explains why patterns hold, backed by a great deal of evidence. The slip to catch is the ladder on which a hypothesis grows up into a theory and then a law: theories do not become laws, and 'only a theory' borrows the everyday meaning of the word.

Why ask it

Not necessarily. Ice cream sales and sunburn climb in the same months because hot weather is behind both, and in other pairs the cause runs the opposite way or the match is luck. Have the class name a third thing that could explain a pair of their own choosing, then say what test would tell the possibilities apart.

Why ask it

If two things change together, nobody can say which one caused the result. A full answer names the three kinds of variable, the one you change, the one you measure and everything you hold steady, and can spot what was left uncontrolled. Give a flawed setup, such as two plants with different water and different windows, and ask what it is able to show.

Why ask it

Outside mathematics, science deals in evidence and confidence more than proof, and every conclusion stays open to revision if better evidence arrives. That does not make everything a guess: some ideas have survived so many tests that doubting them is unreasonable. A good answer avoids both slogans, 'science has proved' and 'nobody can really know'.

Why ask it

New measurements come in, and conclusions are supposed to follow them. It helps to separate the frontier, where findings are fresh and often overturned, from the long-tested core, which changes rarely and usually by refinement. Take it seriously when a child asks with suspicion, because 'they keep changing the story' is a reasonable thing to wonder about.

Why ask it

What was measured, in how many cases, compared with what, and has anyone else found the same thing? Shaky claims tend to rest on one dramatic case, on something for sale, or on a headline that goes further than the finding it reports. Practice on a real example from the week's news, with the class deciding together what they would need to see.

Why ask it

Expect candidates such as what dark matter is, how life first got going, how a brain produces experience and whether the laws of physics can be joined into one account. Stronger replies also say why each is hard, which separates someone repeating a list from someone who has thought about it. Younger students tend to be surprised, and pleased, that there is work left for them.

Why ask it

Keep this one ready for any moment a child asks why. Often the answer is a kitchen test: which things float, what melts ice fastest, whether a seedling bends toward a window. Even when the real experiment is out of reach, working out what you would have to measure is science, and it lasts longer in the memory than being told.