Science Questions for Kids

Why does the moon change shape?

Then ask: Half of the moon is always lit by the sun. What changes about where we are looking from?

Short answer: The moon does not change. As it circles Earth, we see more or less of its sunlit half.

Why do stars twinkle?

Then ask: What does a coin at the bottom of a pool look like when the water moves?

Short answer: Starlight passes through moving air, which bends it a little this way and that, so the star seems to flicker.

Why is it dark at night?

Then ask: The sun does not switch off. Where is it when we cannot see it?

Short answer: Earth spins once a day. At night your side of Earth is turned away from the sun.

Why do we have seasons?

Then ask: Earth is tilted. What happens to the sunlight when your part of the ground leans toward the sun, and when it leans away?

Short answer: Because of the tilt, your half of Earth leans toward the sun for part of the year and gets stronger light and longer days. Half a year later it leans away.

Why does the sun look red at sunset?

Then ask: At sunset the light crosses much more air to reach you. Which color gets scattered out of it first?

Short answer: Low sunlight travels through a lot of air, which scatters the blue out sideways and leaves mostly orange and red.

Why don't we feel Earth spinning?

Then ask: When a car rides smoothly at one speed, can you feel it moving with your eyes shut?

Short answer: We move along with the ground at a steady speed. You feel motion only when the speed or the direction changes quickly.

Why do astronauts float inside a space station?

Then ask: What does your stomach feel at the very top of a swing?

Short answer: The station and everyone in it are falling around Earth all the time. Falling together feels like floating.

Why does the moon have craters?

Then ask: What happens when you drop a pebble into flour or wet sand?

Short answer: Rocks from space hit it. The moon has no wind or rain to wear the marks away, so they stay for billions of years.

Why can we sometimes see the moon during the day?

Then ask: What makes the moon bright in the first place, and is that still happening at noon?

Short answer: The moon is lit by the sun. When it is on our side of Earth during the day, it is bright enough to show through the blue sky.

Why is the sun hot?

Then ask: The sun is not burning like a campfire. What does a fire need that space does not have?

Short answer: The sun is a giant ball of gas. In its middle the gas is squeezed so hard that tiny bits of hydrogen join together, and that gives off heat and light.

Why don't the planets fly away from the sun?

Then ask: When you swing a ball on a string, what keeps it from flying off?

Short answer: The sun's gravity pulls on each planet the way the string pulls on the ball. The planet moves sideways fast enough that it keeps going around.

Why do we hear thunder after we see the lightning?

Then ask: Which travels faster, light or sound? What does a far-off firework tell you?

Short answer: Light arrives almost at once. Sound is much slower and takes about five seconds to cross one mile.

Why does ice float?

Then ask: Does a full bottle of water take up more room or less after it freezes?

Short answer: Water takes up more room when it freezes, so a piece of ice is lighter than the water it pushes aside, and it floats.

Why is the ocean salty?

Then ask: Rivers carry tiny bits of salt from rocks to the sea. When seawater dries up into the air, does the salt go with it?

Short answer: Rivers bring salt washed out of rocks. The sun lifts the water into the air and leaves the salt behind, and this has gone on for millions of years.

Why do we see a rainbow?

Then ask: When you see a rainbow, is the sun in front of you or behind you?

Short answer: Raindrops bend sunlight, split it into colors and send it back toward you. The sun is always behind you when you see one.

Why does the wind blow?

Then ask: What does the air over a hot road do? What moves in to take its place?

Short answer: The sun heats some places more than others. Warm air rises and cooler air flows in under it. That moving air is wind.

Why does a cold glass get wet on the outside?

Then ask: The water did not leak through the glass. Where else could it come from?

Short answer: Air holds water you cannot see. When that air touches the cold glass, it cools and the water turns back into drops.

Why are clouds white and rain clouds gray?

Then ask: How much light gets through a thin curtain, and how much through a thick blanket?

Short answer: A cloud is tiny drops that scatter all the colors of light, which looks white. A thick cloud blocks more light, so its bottom looks gray.

Why is snow white when water is clear?

Then ask: What does a clear ice cube look like after you crush it?

Short answer: Snow is many tiny ice crystals with air between them. Light bounces off all those surfaces in every color, and all colors together look white.

Why does a ship float when a coin sinks?

Then ask: What happens when you push an empty cup down into the bath?

Short answer: A ship is mostly hollow and full of air, so it weighs less than the water it pushes aside, and the water pushes it up.

Why do people put salt on icy roads?

Then ask: Does the ocean freeze as easily as a pond? What is different about it?

Short answer: Salty water freezes at a lower temperature than plain water, so the salt melts the ice unless the day is very cold.

Why is it colder on top of a mountain, closer to the sun?

Then ask: The sun is 93 million miles away. Does one mile closer matter? What else is different up there?

Short answer: The air up high is thinner and holds less heat. Being a mile or two closer to the sun makes no difference.

Why do dogs sniff everything?

Then ask: What do you use most to learn about a new place: your eyes, your ears or your nose?

Short answer: A dog's nose is far more sensitive than ours. Smell is its main way of learning who has been somewhere and what happened there.

Why do leaves change color in the fall?

Then ask: The yellow is in the leaf all summer. What might be hiding it?

Short answer: The green stuff a leaf uses to make food covers its other colors. In fall the tree stops making it, and the yellow and orange show through.

Why do bees make honey?

Then ask: What do bees eat in winter, when there are no flowers?

Short answer: Honey is food the bees store for winter. They make it from the nectar they collect from flowers.

Why don't fish drown?

Then ask: What do we take from the air when we breathe? Could the same thing be in water?

Short answer: Water has oxygen mixed into it. Gills take that oxygen out as the water flows over them.

Why don't birds get shocked on a power line?

Then ask: Electricity needs a path from the wire to somewhere else. Is the bird touching anything besides that one wire?

Short answer: Electricity flows only when it has a path to the ground or to another wire. A bird sitting on one wire gives it no such path.

Why don't spiders stick to their own webs?

Then ask: If you built a trap out of glue, how would you get across it yourself?

Short answer: Only some threads in a web are sticky. The spider walks on the dry ones and touches the sticky ones with just the tips of its legs.

Why can owls see so well at night?

Then ask: What do your own eyes do after a few minutes in a dark room?

Short answer: Owls have very large eyes with wide pupils that gather a lot of light, and many of the cells that work in dim light.

Why do snakes stick out their tongues?

Then ask: A snake's tongue has two tips. What could two tips tell it that one could not?

Short answer: The tongue collects smells from the air and carries them to a sensor in the roof of the mouth. The two tips help tell which side a smell comes from.

Why do plants grow toward the window?

Then ask: What does a plant need in order to make its food?

Short answer: Plants need light to make food. The shaded side of the stem grows faster than the lit side, and that bends the plant toward the light.

Why do bears sleep through the winter?

Then ask: What would a bear find to eat in January?

Short answer: There is little food in winter. A bear eats a lot in the fall, then slows its body down and lives on stored fat until spring.

Why do whales come up to the surface?

Then ask: Whales are not fish. What do they have that fish do not?

Short answer: Whales are mammals with lungs. They breathe air through a blowhole on top of the head.

Why do we get goosebumps?

Then ask: What does a cat or a bird do with its fur or feathers when it is cold?

Short answer: Tiny muscles pull your hairs upright when you are cold or startled. On an animal with thick fur, that traps warm air.

Why do fingers wrinkle in the bath?

Then ask: Car tires have grooves. What are the grooves for on a wet road?

Short answer: Your nerves make the blood vessels under the skin narrow, and the skin puckers. Scientists think the wrinkles may help you grip wet things.

Why do we blink?

Then ask: What happens to your eyes if you try not to blink for a whole minute?

Short answer: Each blink spreads tears over the eye to keep it wet and clean. Blinking also protects the eye when something comes close.

Why do we need sleep?

Then ask: How do you think and feel the day after a very short night?

Short answer: While you sleep, your brain sorts and stores what you learned, and your body repairs itself and grows.

Why do baby teeth fall out?

Then ask: Would the teeth you had at age three fit your mouth when you are grown?

Short answer: Your jaw grows and needs bigger teeth. Adult teeth push up from underneath, and the roots of the baby teeth dissolve until they come loose.

Why do we sweat?

Then ask: How does your skin feel when you step out of a pool into the wind?

Short answer: Sweat dries off your skin and takes heat away with it. It is how the body cools itself.

Why do we get dizzy after spinning?

Then ask: When you stir a cup and then stop the spoon, does the water stop right away?

Short answer: Liquid deep inside your ears keeps moving after you stop, so for a moment it tells your brain you are still turning.

Why does your stomach growl?

Then ask: Which sounds louder when you tap it, an empty drum or a full one?

Short answer: Muscles in your stomach and intestines squeeze to move food, liquid and gas along. It is louder when there is little inside.

Why do we have two eyes and not one?

Then ask: Close one eye and try to touch the tips of two pencils together. What changes?

Short answer: Each eye sees from a slightly different spot. Your brain compares the two pictures to judge how far away things are.

Why is blood red?

Then ask: Blood's main job is to carry something from your lungs to the rest of you. What is it?

Short answer: Red blood cells are full of a substance that holds iron and carries oxygen. That substance is red.

Why can't you tickle yourself?

Then ask: What is different about a touch you expect and a touch you do not?

Short answer: Your brain predicts what your own touch will feel like and turns the feeling down. A touch from someone else is a surprise.

Why does metal feel colder than wood in the same room?

Then ask: Both are the same temperature. Which one carries heat away from your hand faster?

Short answer: Metal moves heat away from your skin quickly, so it feels cold. Wood moves heat slowly.

Why does a magnet stick to the fridge and not to a wooden door?

Then ask: Try a magnet on a few metal things. Do all of them stick? What might the ones that stick share?

Short answer: Magnets pull on iron and a few other metals. A fridge door is steel, which is mostly iron. Wood has none.

Why does bread rise?

Then ask: Look closely at a slice of bread. Where did the holes come from?

Short answer: Yeast is made of tiny living things. They eat the sugar in the dough and give off gas, and the gas bubbles puff the dough up.

Why does popcorn pop?

Then ask: What does water turn into when it gets very hot? What if it has no room to get out?

Short answer: Each kernel has a little water inside. Heat turns it to steam, and the steam pushes until the hard shell bursts.

Why does a balloon stick to the wall after you rub it on your hair?

Then ask: What does your hair do right after you rub the balloon on it?

Short answer: Rubbing moves tiny electric charges onto the balloon. That static charge pulls the balloon toward the wall.

Why does a straw look bent in a glass of water?

Then ask: Does the straw feel bent when you run a finger along it? So what is being bent?

Short answer: Light bends when it passes from water into air, so the part of the straw under water seems to be in a different place.

Why does soap get your hands clean?

Then ask: What happens when you rinse greasy hands with water alone?

Short answer: One end of a soap particle grabs grease and the other end grabs water. When you rinse, the water carries the soap and the grease away.

Why do onions make you cry?

Then ask: Your eyes water when smoke gets in them too. What are the tears trying to do?

Short answer: A cut onion gives off a gas that stings your eyes. Your eyes make tears to wash it out.

Why do you hear an echo?

Then ask: Where have you heard an echo, and what was in front of you there?

Short answer: Sound bounces off a hard surface far away and comes back to you a moment later.

Why does an airplane stay up?

Then ask: What does your hand feel when you tilt it in a strong wind?

Short answer: The wings are shaped and tilted to push air downward as the plane moves fast. The air pushes the wings up in return.

Why does a mirror show your face when a wall doesn't?

Then ask: Can you see yourself in a still pond? What about when the wind ripples it?

Short answer: A mirror is so smooth that light bounces off it in order and keeps the picture. A wall is rough and scatters the light every which way.