The Why Bank: Quick Answers to Kids’ Why Questions

Air is made of gas particles that are super tiny and spread far apart. Light passes right through them, so air looks like nothing. But you can feel it when it moves, like wind on your face.

A big fan called the blower pushes air through tubes called ducts. The air comes out of the vents, usually in your ceilings. Then it gets pulled back to the machine through the big return grille, usually on a hallway wall or ceiling.

Air that goes into a room needs a way back. Without the return, the machine would run out of air to push. Try it: find the big return grille and check that no furniture, toys or laundry block it.

The sun warms some places more than others. Warm air spreads out and rises, and cooler air rushes in to fill the space. That rushing air is wind.

Moving air carries body heat away from your skin and helps sweat dry. The room isn’t any colder. That’s why fans cool people, not rooms. Turning a fan off when you leave the room is a smart habit.

Cold air particles slow down and don’t push as hard on the balloon’s walls, so the balloon shrinks a little. Warm it up and it grows again. Try it: see the Hot Air Rises lab.

Tiny bits of lint, fur, dirt and crumbs are so light they float. Every time you walk, sit on the couch or shake a blanket, more dust floats up.

It catches the dust, fur and lint floating in your house air. Over weeks, all that dust piles up and turns the filter gray. Grown-ups change it so air can flow easily.

Air pressure changes as you go up or down. Your ears have a little pocket of air inside. When the pressure outside changes, the air inside adjusts with a pop.

When you sip, you lower the air pressure inside the straw. The air outside is still pushing down on your drink, so it pushes the drink up the straw into your mouth.

Moving air pushes on doors. When the heater or AC blows air into a room, a door left open a crack can swing. Wind through an open window can do it too.

Water vapor in the air touches the cold glass and turns back into drops. That’s condensation. The water comes from the air, not from inside the glass. Try it: Cloud in a Glass.

The indoor coil is very cold. Water vapor in your house air condenses on it, drips into a pan and flows out a pipe. Every drop came out of the air you live in.

The water evaporates. Bits of water at the top get enough energy from the sun and air to float off as invisible water vapor. Sun and wind make it go faster.

Clouds are made of drops so tiny that rising air holds them up. When the drops bump together and grow big and heavy, they fall as rain.

The air you blow out is warm and has water vapor in it. When it hits cold air, the vapor condenses into tiny drops, making a little cloud.

At night, grass cools down below the air’s dew point. Water vapor condenses on the blades as dew. The morning sun evaporates it.

As water evaporates from your hair, it takes heat with it. That leaves your head feeling cooler. Try it: Cool by Evaporation.

Winds often blow in from the Gulf of Mexico, bringing air full of water vapor. That damp air makes summer feel sticky.

The glass is colder than the dew point of the air touching it, so water vapor condenses into tiny drops. In winter it’s usually inside the glass. In summer it can be outside.

When water freezes, its particles line up in a pattern with more space between them. That makes ice a little lighter than the same amount of liquid water, so it floats.

It actually moves heat. It takes heat out of your house air and carries it outside. The air left behind feels cool. Read How does an air conditioner work?

Fast-jiggling particles bump into slow ones and speed them up. That passes energy from the hot thing to the cold thing until they’re the same temperature.

Metal is a conductor. Heat travels easily through it, from the soup up to the handle. A wooden spoon is an insulator, so its handle stays cooler.

Dark colors soak up more sunlight and turn it into heat. Light colors bounce more sunlight away. Try it: put a dark and light paper in the sun, wait 10 minutes and touch both. Which was warmer?

A blanket doesn’t make heat. It traps the heat your body makes, so it leaves more slowly. Fluffy blankets trap lots of air, and trapped air is a great insulator.

The AC moves heat at a steady speed. Setting the thermostat much lower doesn’t make it go faster, just like pressing harder on a doorbell doesn’t make it ring louder. It just runs longer.

The sun beats on the roof all day. The roof heats the attic air, and that heat is trapped up there.

Even cold outside air has some heat in it. A heat pump’s outside coil gets colder than the air, so heat flows into it. Then the heat pump carries that heat inside. Read How does a heater work?

Rubbing makes friction. Friction turns the energy of moving into heat. That’s why rubbing your hands on a cold morning feels nice.

Its walls are thick foam, which slows heat from getting in. The ice melts slowly because heat has a hard time reaching it. Try it: Keep It Cold.

A switch inside it flips on or off when the thermostat calls. Switches make a click. A click and then a hum means it’s starting.

The compressor inside is a strong pump. Pumps vibrate and hum while they work. The big fan on top adds a whooshing sound.

Wood and metal shrink a tiny bit as they cool off at night. Those tiny moves make creaks and pops. Quiet nights let you hear them.

Air squeezing through a narrow space speeds up, and fast air can whistle, like blowing across a bottle top. If a whistle is new or very loud, tell a grown-up.

Sound is a wiggle that passes from particle to particle. Walls wiggle a little too, so some sound gets through. Soft, thick stuff soaks up more sound.

Light travels super fast and reaches you right away. Sound is much slower. Count the seconds between flash and boom. Bigger numbers mean the storm is farther away. When thunder roars, go indoors.

The fridge has its own little compressor and fan. They buzz while they work, then rest when the inside is cold enough.

Loud banging, grinding, squealing or a new sound that doesn’t stop can mean a machine needs a check. You don’t need to know what’s wrong. Just tell a grown-up. See House Sounds.

During the day, cars, voices and TVs hide the sound. At night, those sounds fade, so the steady hum stands out.

Baking cookies send tiny smell particles into the air. Moving air carries them through the house to your nose. Your nose catches them and your brain says “cookies!”

Rain knocks loose oils from plants and stuff from the soil and sends them into the air. Many people love that smell after a dry spell.

Heat helps more smell particles float off things into the air. More particles reach your nose, so the smell seems stronger.

Your nose gets used to smells it smells all the time and stops noticing them. That helps it notice new smells instead. Visitors may notice smells you don’t.

When grass is cut, the blades release smelly particles into the air. That fresh, green smell is the grass’s juices drifting to your nose.

When air doesn’t move, smells build up in one place. Opening a door or running a fan mixes in air from other rooms.

Your nose is a great detector. If you smell something new from a vent, a machine or anywhere in the house, you don’t have to figure it out. Just tell a grown-up right away.

Dogs have many more smell sensors in their noses than people do, and a big part of their brain works on smells. They can notice smells we never could.

The fridge is a closed box. Smell particles from food stay trapped inside and mix together. Covering food keeps smells from spreading.

Austin is fairly far south, so the summer sun shines high in the sky and heats things a lot. Warm, damp air from the Gulf adds stickiness. Some summers have many days that reach 100 degrees.

When the air is humid, sweat dries slowly, so your body can’t cool off as well. The heat index is a “feels like” number that adds humidity to the temperature.

A strong cold front pushes a big mass of cold air down from the north. When it arrives, the cold air shoves out the warm air in a hurry. See Austin Whys.

Damp air holds onto heat, and the ground, roads and buildings soak up heat all day and give it back slowly at night.

The sun heats the ground, and warm, damp air rises fast. As it rises, it cools and the water vapor makes tall clouds. Those can grow into storms.

Moving water can be much deeper and stronger than it looks. Weather experts say “Turn Around, Don’t Drown.” Grown-ups find another way.

Most winters, a few cold fronts bring air cold enough to freeze water. On those nights, grown-ups cover plants and protect pipes.

Sunlight bounces inside raindrops and splits into colors. The light comes back to your eyes at the same angle from every drop, which makes a circle shape. The ground hides the bottom of the circle.

Something is blocking the sun’s rays from hitting you and the ground. Trees are extra cool because water evaporates from their leaves. See Shade Squad.

Inside tall storm clouds, it’s freezing cold high up. Strong winds toss raindrops up and down until they freeze into balls of ice too heavy to stay up.

Dogs don’t sweat like people do. Panting moves air over their wet tongue and mouth, and the evaporating water carries heat away. Give pets shade and water on hot days.

Tile is a good conductor, so it pulls heat away from the cat’s body. Cats are smart about finding the coolest spot in the house.

Their big, thin ears have lots of blood vessels close to the surface. Heat can leave through the ears into the air, helping the jackrabbit stay cool in hot places.

In the warm months, a huge group of bats lives in narrow cracks under a bridge downtown. The tight, dark spaces are cozy and safe for them. They fly out at dusk to eat bugs.

Fluffed feathers trap air, and trapped air is a great insulator. It’s like the bird putting on a puffy jacket.

Lizards can’t make much of their own body heat. They warm up by lying in the sun, then move to shade when they get too warm.

On hot days, honeybees fan their wings to move air through the hive, like a tiny air conditioner. They also spread water that cools as it evaporates.

Standing close together means less of each penguin’s body touches the icy wind. They share warmth and take turns in the middle.

The big grille, called the return, is where the AC breathes in. A pet bed or crate in front of it blocks the air. Try it: check that the grille is clear. See Pet Comfort Patrol.

Like jackrabbits, elephants have huge ears with blood vessels near the surface. Flapping moves air over them so heat can leave faster.

Underground stays cooler in summer and warmer in winter than the air above. A burrow is a cozy home that keeps the temperature steady.