Before food gets into your kitchen, before it even gets to the store, it’s on a farm. Almost everything we eat is grown on a farm, an area of land used to raise animals and plants. Farming nowadays can get pretty complicated. Farmers are scientists – agricultural scientists. Farmers work hard to keep their farms healthy. Soil is stirred up to get oxygen to the microorganisms that live in between the grains and to plant roots – that’s called tilling the soil to aerate it. Plants need to be protected from pests with either chemical pesticides or biological pesticides. Animals like bats and friendly insects eat other pest insects (chomp,chomp). Animals are milked, corralled, fed, sheared, slaughtered or cleaned-up after.

Towers, teepees, castles, and condominiums – some kind of planning goes into all buildings, no matter how big or small. Architects are people who design buildings, and the areas around buildings. Usually architects draw on a computer or a big desk (a drawing board). The plans show the dimensions of all parts of a building. Architects try to design with the purpose of the building in mind, but even buildings used for the same thing can look very different.

Worms, squid, clams, and flies are spineless creatures. They’re not afraid, they’re invertebrates – animals that don’t have backbones. Invertebrates are everywhere. You can find invertebrates in the sea, in freshwater, and on land. There are about 30 times more invertebrates than vertebrates on Earth.

Volcanoes are mountains made from molten rock. The Earth’s crust is divided into big slabs, called plates, which are slowly moving all the time. The plates are floating on the Earth’s mantle, a layer of gooey hot rock that flows like maple syrup. Some places in the mantle, the rock gets very hot and nearly liquid. It’s called magma. Sometimes the magma reaches the Earth’s surface and forms a volcano.

Frogs, toads, salamanders, newts, and caecilians (worm-like animals that have backbones) are all amphibians, animals that spend part of their lives in water and part on land. Amphibians are slimy. Amphibians are cold-blooded that means their body temperature changes with the temperature outside. And as amphibians grow up, they go through metamorphosis.

Whales, dolphins, otters, walruses, and orcas are just like us, they’re mammals. Well, they’re not just like us. They live in the ocean. They breathe air, have hair, nurse their babies, and they are warm-blooded. They keep the same body temperature all day. To do that in the ocean isn’t easy. Water soaks up heat, so the ocean is really pretty cold. Marine mammals have all sorts of ways to keep warm. Whales, dolphins, and walruses have thick layers of fat called “blubber.” It’s great insulation. It holds their body heat keeping them warm in the cold ocean. Sea otters have thick layers of fur that cover their whole bodies. Otters fluff their fur to trap air between the hairs. It helps them float, it the air keeps them warm even when they dive deep hunting for food. These adaptations make it possible for marine mammals to live all over the world’s oceans.

Water is massive; rivers are powerful. As rivers flow downhill, they wear away rock and soil to form canyons or winding curves in the land, called meanders. Sometimes rivers fill and overflow their banks. Rivers with too much water create floods that can carry away plants, trees, buildings and boulders. Rivers and streams support most of the ecosystems on land.

Did you know that the Concorde moves 300,000 times faster than a land snail? Or that a giant redwood can be as tall as a 35-story apartment building? The only reason we can make these comparisons is because people have measured these things. We don’t compare jets and snails every day, but we do rely on measurement constantly. When you take your temperature, you find out how it compares to the temperature of someone who is healthy. When you bake brownies, you’ll need to measure the ingredients first to make sure they turn out tasty. Using measurement, we can make useful comparisons of distance, time, mass, and temperature.

How do noses work? Objects give off tiny amounts of tiny molecules into the air. When just a few of these molecules get up your nose, they dissolve in the mucus up there. Some molecules come into contact with special receptors on what’s called your “olfactory membranes.” Each nostril has a membrane, and each membrane is only about the size of a postage stamp. The membranes hold millions of receptor cells, each of which are ready to send messages to the brain about the molecules that go up your nose.

Look no further ... Bill Nye is on the ball - the eyeball. For their small size, your eyes do an important job. By working with your brain, your eyes can tell the difference between thousands of different colors. They can follow a fast-moving hockey puck across the ice. They are even sending messages to your brain about what you're reading right now. Eyes work a lot like a camera. They take in light, focus light, and make images. With help from the brain, your eyes help understand the world around you. Light bouncing into your eye passes through an opening called the pupil. If you look in the mirror, your pupil is the black area in the middle of your eye. The pupil can open or close, depending on the brightness of the light. After passing the pupil, the light is focused onto the back of your eye by the lens, a thin layer of cells. On the back of your eye are special cells called rods and cones that are sensitive to light. These cells send electrical messages to your

Earthquakes happen when pieces of land in the Earth’s crust scrape together. The crust of the Earth is made of big slabs of land called plates that are constantly moving just a little bit. The plates scrape by one another, and sometimes they don’t move smoothly. An earthquake happens when the plates get unstuck suddenly and jerkily slip past each other. The majority of earthquakes occur along plate boundaries such as the boundary between the Pacific Plate and the North American plate. One of the most active plate boundaries for earthquakes is the massive Pacific Plate commonly referred to as the Pacific Ring of Fire. The fire comes from the volcanoes that form near the edge of the plates.

Dirt, sand, and rock from the Earth’s surface gets blown, sliced, torn, swallowed and distributed all over the world. What was yesterday’s hill is tomorrow’s flat plain. The planet looks a lot different than it did when it formed four and a half billion years ago. The force of erosion, the slow wearing away of the land, has never ceased.

The show is way out there, way far away. After all, it's in Outer Space. When you look at the night sky on a clear dark night, you can see thousands of stars. There are far more than you could count. And, they are way out there. They are very, very far away. It's about the hardest thing to imagine about space. Let's talk about the nearest star to us, the Sun. If somehow outer space were not an icy cold vacuum with nothing to eat, drink, or breathe, and we could drive there in a car, to get to the Sun at freeway speed of 100 kilometers/hour (61 miles/hour), it would take171 years of driving without stopping to sleep or get gas out in the near nothingness of space. That's just to the Sun. To get to even the closest star, Proxima Centauri, would take 40,000 years. On top of that, most things, billions and billions of stars, are much, much farther away than that! It is just astonishing. How do we know that everything is so far away? We have watched the sky for centuries.

Dirty water, land, and air are a result of pollution. People are the only animals on Earth that make pollution. Garbage, burning fuel, chemicals, sewage, oil, and pesticides are all human-made things that make the Earth’s atmosphere, water, and soil unclean. Humans are even leaving trash in space, such as broken satellites, pieces of metal, paint from rocket skin, and even cameras and toothbrushes. Much of the junk people make and leave behind hurts plants, animals, you and me.

Bill and actress Candace Cameron use fire to demonstrate what chemical reactions are.

Caves come in all different shapes and sizes depending on how they were formed. Spelunkers (people who explore caves) have plenty of descriptive names for caves and the natural rocky features that form within them – soda straws, fried eggs, popcorn and draperies are just a few. Caves can be as simple as one straight passage with a few stalactites overhead, or as complex as a labyrinth, with many stalagmite-carpeted rooms.

Be sure to get this straight: spiders are not insects, they’re arachnids. Spiders have eight legs, and insects have only six. Spiders have two body parts, a head and an abdomen, while insects have three body parts, a head, a thorax, and an abdomen. Insects have antennae, and spiders do not. Some insects sting. All spiders have fangs and venom. There are almost certainly a few spiders in the room with you right now.

A lot of things spin – bike wheels, footballs, hard disks in your computer, and even the Earth – they’re all twirling around. Spinning things have inertia, which means they keep spinning unless something slows them down. Bike tires keep spinning until you put on the brakes. A football spirals through the air until you catch it. The Earth keeps on spinning 24 hours a day, seven days a week. It’s been spinning for over four billion years.

When you push something, you’re using pressure. Pressure depends on two things – the power of the push and the area that’s being pushed on. A push on a small area makes more pressure than the same size push on a big area. Pushing hard on something creates more pressure than a little nudge, naturally.

Bill Nye's going to use the force to pull you into the world of balance. A force is a push or a pull. You can feel a force when someone pushes you. You can use a force to pull a door shut. Anyone can make forces by pushing and pulling, and you don't need to be Luke Skywalker to use a force. In a game of tug-of-war, if the pull of your team is the same as the pull of the other team, the forces are equal. The two teams are in balance, and the rope doesn't budge. Things are in balance when forces that are pushing or pulling them are equal. If your tug-of-war team pulls harder than the other team, the forces are not equal. The other team falls all over the place. Unequal forces make things move and twist. A lot of things are designed to take advantage of unequal forces. Wrenches, screwdrivers, door handles, and water faucets use forces made by you to do work. A well-balanced science diet starts with Bill Nye.

Don't stay in the dark - Bill Nye will help you absorb the science of light optics. Light is energy that normally moves in a straight line, but often something gets in the way. When light runs into something, three things can happen - the light can bounce off, it can go through, or it can be absorbed. Often all three things happen at the same time. Light bounces off mirrors. You see yourself in a mirror when light bounces off your face, into the mirror, and then into your eyes. Light goes through glass. If the glass is bent or curved, the light gets bent on its way out of the glass. The glass in a magnifying glass or a pair of eyeglasses is curved so that it bends light, making things look bigger. More light is absorbed by dark-colored things than by light-colored things. Colors are made when some light is absorbed while other light is bounced back. Black things look black because when light hits them, they absorb almost all of the light.

Are you tense? Need some structure to your life? Then tune in to Bill Nye the Science Guy as he explains the science of structures. All structures give support or create a shape. You can find structures everywhere. Bridges, buildings, chairs, shoes, plants, spiderwebs, tables, and even your own body are all structures. A structure's shape, size, and what it's made of depend on what the structure does and how strong it needs to be. When structures give support, they either experience a pull (tension) or a push (compression). Structures in tension, such as ropes, cables, or blimps are made from stuff that is good at pulling. The materials in tension are usually thin. Structures under compression, such as elephant legs and courthouse columns, are made from hard stiff stuff. Compared to structures under tension, structures under compression are much thicker. When it comes to structures, form (the size and shape) depends on function (what it does). Build support for Bill

Lighten up. It's the ""Light and Color"" episode. Without light, we wouldn't be able to see. It would be like living in a room with no windows, doors, or lamps. There's an old saying, ""We don't see things; we see light bouncing off of things."" We see things, and colors, when light bounces off things and into our eyes. White light, like the light from the Sun, is made up of all the different colors of light blended together. When white light hits something white, almost all of the light bounces into our eyes, and we see the color white. Things are different colors because some light bounces off and other light gets absorbed. An orange is orange because it absorbs all different colors of light except orange light. Grass is green because it absorbs all different colors of light except green light. Bill Nye's lab coat is blue because it absorbs all different colors of light except blue light. All colors, including black, are made in the same way. It's just a matter of ref

Your heart pumps your blood around your body, all hours, every day of the week, to keep you alive. Your heart is about the size of your fist, and it’s made of special muscle called “cardiac” (KAR-dee-ak) muscle. Cardiac muscle lets your heart keep the beat, it can also speed up or slow down, depending on what your body needs. Your heart works like an automatic pump – it squeezes, or contracts, and un-squeezes, or relaxes, to push blood through the four different sections of your heart. Valves, special one-way openings, are like little doors between the sections – making sure your blood moves in only one direction through your heart, to your lungs, back to your heart, and then around your body again.

It doesn't matter if it's spring, summer, winter, or fall - Bill Nye is always in season. Every year, we experience the seasons. Some months have snow and rain, while other months have warmth and sunshine. Temperatures go from cold, to woarm, to cold again – winter, spring, summer, and fall. The cycle of the seasons takes one year, and the Earth takes one year to go around the sun. Coincidence? No way. The Earth's orbit around the Sun is flat, as though our planet were spinning over a tabletop. Compared with flat plane of its orbit, the Earth is tilted. Its axis, the imaginary line between the North and South Poles, is tipped over a bit. In June, the north half of the Earth (the Northern Hemisphere) is tilted toward the Sun, and it's summertime in places like Nye Labs in the United States. Meanwhile, the south half (the Southern Hemisphere) is tilted away from the Sun, and it's winter there, in places like Australia and South Africa. The Earth's orbit isn't quite

Let the moon master Bill Nye teach you the ancient and not-so-ancient secrets of the Moon. Wax on, wax off. The Moon grows bigger (waxes) and smaller (wanes) every 30 days or so. The word ""month"" comes from the word ""moon"". The Moon is the closest thing in space to Earth, and it's one of the most well-studied orbs in our solar system. We know that Moon rocks are rich in calcium and aluminum, that the Moon has no atmosphere, and that there are over a million craters on the Moon's surface. The Moon doesn't glow on its own, it reflects sunlight. Watch the Moon every night for a month as it grows, shrinks, and at one point disappears. The Moon doesn't actually change it's shape. It's the way the sun shines on the part of the Moon we see that makes the phases change. The Earth moves around the Sun, the Moon moves around the Earth. As the Moon moves through its orbit, the Sun shines on bigger or smaller portions of it. If you were looking at the Moon from the Sun, it woul

Ocean exploration is a tricky, risky business since humans can’t naturally survive under the ocean. Ocean explorers are constantly inventing new tools to help them dive deep into the sea. Over the last few hundred years or so, and especially in the last few decades, we humans have come up with all kinds of new ways to study the ocean. Even so, the ocean remains largely unexplored. It’s huge, cold, salty, and deep. Ocean exploration helps us understand our planet, and may help us solve the mystery of how life started on Earth.

Feeling a little hungry? Then grab a snack and watch Bill Nye the Science Guy's episode on the Food Web. When it comes to eating, all living things depend on other living things. Take a chicken sandwich, for example. The bread came from plants. So did the lettuce and tomatoes. The cheese was made from milk, which came from a cow. To make milk, the cow had to stay alive by eating grass. The meat came from a chicken who once ate seed, and maybe the occasional bug. The animals that helped to make your sandwich depended on other living things to survive. The lettuce, grain (for the bread), and tomato got by fine on their own. Then some animal came along (you). Plants are the only big living things that don't need other living things to survive. All they need are sunlight, carbon dioxide, and water to make their own food. But it doesn't stop them from being eaten -- no way. In fact, plants are great things to eat. All animals need them in some way for food – by the way,

Flowers are an important part of many plants. Plants use flowers to make other plants – to reproduce. Flowers have special parts, called stamens and pistils. When pollen from the stamen finds its way down through the pistil, the flower is pollinated, and seeds start to grow. The seeds eventually find their way to the ground, the seeds sprout, and more plants are born.

Fluids are cool; they ooze and swoosh. Whatever container you put a fluid in, that fluid will take the same shape. Milk poured into a pitcher forms to the shape of the pitcher. If you pour it into a glass, it takes the shape of the glass. You just can’t do that with a boulder. But with the right container, you could pour liquid rock from below the Earth’s crust. Fluids still act like fluids, even halfway to the center of the Earth.

The relationship between the Earth, the sun, the wind and the weather. Guest: "Today" weather reporter Willard Scott.

In this program, Bill points out the different ways in which humans and animals exchange information. He also talks about the ability of humans to store data in computers, books, and on videotapes.

Atoms are reeeeally small. They are so small that you can’t see them with just your eye. It takes as many as 10 million of them side-by-side to measure a single millimeter. In fact, atoms are the smallest pieces of “stuff” that are still considered “stuff.” If you take something and break it into tiny pieces, and then break it into tinier pieces, and keep going, the smallest part you’d be left with (and still have the same substance that you started with) is an atom. Atoms are the building blocks of all matter. Everything is made of only 109 different kinds of atoms, called elements. 92 of these elements occur naturally, but the rest of them – ones like Technetium and Promethium have only been found in distant stars and Californium and Einsteinium – are only made in laboratories. A molecule is born any time two or more atoms combine together. English

The momentum of a moving thing, like you riding your bike, depends on how much mass you and your bike have and how fast you’re speeding down that hill. An elephant on a bike has more momentum than a mouse on a bike moving at the same speed. A mouse on a fast bike has more momentum than a mouse on a slow bike. If there’s an elephant on a fast bike, you’d better get out of the way.

Bill Nye teaches us about reptiles.

Energy, things like light, heat, and sound, moves in waves. You’ve probably seen waves in the ocean, or ripples when you throw a rock in a pond. Moving energy is not like the wave you do with your hand.

Surf's up! Get the current information as Bill Nye explains why oceans are salty and explores the ocean currents. Go with the flow of ocean currents with Bill Nye the Science Guy. Most of the Earth is covered with water - we're talking 71% of the entire Earth, and most of that water is in oceans. It depends how you count, but you can say that there are five oceans on Earth - the Atlantic, the Pacific, the Indian, the Arctic, and the Antarctic. They are all connected into one World Ocean by the flow of ocean currents. Ocean water is moving around all the time. Some of the moving water forms rivers in the ocean. Oceanographers, scientists who study oceans, call these rivers of ocean water "currents". Currents help sea animals move around, they bring up deep ocean water with lots of nutrients for small animals to eat, and they push warm and cold water around, creating different climates in the oceans. As the sea surface gets warmed by the Sun, water evaporates, but salt stays in the sea.

How breathing supplies the body with the oxygen it needs

Wetlands are not just home to different animals and plants, but they also control flooding and help keep the Earth’s water clean. Flood waters move more slowly through wetlands because they have to go through barriers of plants and dirt. Wetlands help stop erosion because the plants stop the soil from washing away. Plants and soil in wetlands slow water enough that bacteria and other decomposer organisms can break down and even absorb some types of pollution. Wetlands are wet. Let’s keep them that way.

The air that surrounds Earth is called the atmosphere. Compared to the size of the Earth, the atmosphere is very, very thin. It’s made from gases – mainly nitrogen, oxygen, and water vapor, with a little argon, carbon dioxide, xenon, neon, helium, and sulfur. The atmosphere does a lot for Earth. It blocks ultraviolet light and burns up a lot of meteors. It traps in heat, keeping Earth cozy. Even clouds are formed in the atmosphere – keeping the Earth wet with rain.

It's time for Bill Nye to shed a little light on electricity. Electricity might seem mysterious, but once you understand the science the light goes on (so to speak). You flip a switch, and the lights turn on. You push the play button, and your personal stereo starts playing music. When you flip the switch or push play, you start a flow of electrons. Electricity is the flow of electrons, and electrons are very tiny charged particles. Electrons are found in atoms, the tiny pieces that all stuff is made from. We can make electrons flow in two ways. Batteries make electricity by mixing up chemicals -- making a chemical reaction that forces electrons to move in a path from the battery to the personal stereo and back to the battery. Electricity that turns on lights in your home is made by power plants. Most power plants use big machines called generators to make electrons by twirling wire in a magnet. The magnet makes electrons in the wire move around, creating electricity.

Join Bill Nye as he counts down the hits from the Soundtracks of Science. Along with the music, Bill does a few new experiments on the lab bench. You’ll see the grunge band Nyevana’s classic “Air Pressure,” Momentisey’s “The Faster You Push Me,” and divas En Lobe’s “Whatta Brain.” There’s even a special appearance by Mudhoney, a real band from Seattle. But if you want to know who’s the number one artist from Not That Bad Records, you’ll have to tune in.

Every time you look at something, hear something, touch something, smell something, or taste something, your brain collects a little information about the world around you. You may even have a scrapbook to store memories of some of that information. There’s a lot out there though. How do people sort out the valuable information from the not-so-valuable?

In Bill Nye the Science Guy: Forests, Nye shows students the levels of a forest, which include the canopy, the under story, and the floor. His special guest is Nalini Nadkarni, who has no qualms about going high up in the canopy to check out the wildlife and other happenings there

Actress Elaine Miles and Bill Nye explain why static electricity makes clothes stick together.

There are lots of different climates all over the world. Deserts are warm and dry. Temperate forests are cold and wet. Tropical rain forests are warm and wet. Animals and plants live in climates that are good places for them to live. Cacti wouldn’t grow too well in the Arctic, just like polar bears would over heat in the desert.

Music is the art and science of expressing ideas and feelings through sound. A sad song can say more about how someone feels than most words, and a familiar song can make crowds clap together and feel like one happy family. Whatever the emotion, music seems to have a way to communicate it. The music we listen to today is the result of years of experimentation with sounds. As people figured out what they liked best, they invented instruments that could play their favorite tones and developed popular rhythms, or patterns of beats. Each note of music, and every tone of each instrument is a sound wave. Some sound waves sound great together. Some not so good. Getting the exact soundwaves in the pattern you want – now that’s science.

You can't see them, but they're everywhere even inside Bill Nye. This is not science fiction, it's the science of cells. All things that live are made from cells. You can't see them, but every part of your body, including everything inside your body, is made from cells. Cells eat, they grow, and they make more of themselves (what scientists call replicate). There are millions of different types of cells. Dog cells are different from fish cells. Bird cells are different from your cells. And inside your body, there are many different cells, each one doing a different job to keep your body going. Cells may be tiny, but without them, we'd be nothing.

In this show, you can Bone up on Muscles. When you clicked on the Nye Labs web site to read this, you used your bones and muscles. Without them, you can't click, surf, or even sigh. Bones and muscles work together, or you aren't going anywhere. Muscles always pull, even when you push on something like a door somewhere in your body your arm and leg muscles are in tension. They are all attached to bones, and those bones are pushing; they're in compression. By pulling on bones you can breathe, talk, and move all over the world. Your bones support your weight like beams of steel or wood. They're stiff and strong. Rigid as they might seem though, they do flex. And, if you bang one hard enough, it swells up. You have a lump. That's because bones are full of blood vessels. Bones are not solid like rocks or skeletons in a dinosaur museum. Bones flex and grow. In fact, putting healthy amounts of stress on your bones is good for them.

A plant’s recipe for food has only three main ingredients: sunlight, carbon dioxide, and water. When plants make their food, they give off what animals need – oxygen. Without oxygen, animals like us wouldn’t be able to breathe. If plants weren’t here on Earth, we wouldn’t be here.

A hot-air balln ride and a trip to the aquarium help Bill Nye explain why things float

More than 22,000 different species of fish live in the oceans, lakes, and rivers of the world. Fish come in all shapes and sizes. Some eat water plants, some eat other fish. Lampreys and some jawless fish suck onto other fish for food. Stone fish live on ocean bottoms and camouflage themselves as rocks. Puffer fish blow themselves up like a balloon, only they’re covered with spines. There are tons of strange and cool-looking fish everywhere.

Probability is a way to measure how likely it is that something will happen. Probabilities are predictions. They’re often just very careful guesses. When a scientist wants to calculate a probability, she or he gathers data and then uses the data to make her or his guess. Probabilities are between 100% (it’s definitely going to happen) and 0% (forget about it, pal, it’s not going to happen). Most things have a probability somewhere in between.

The color of your eyes, the shape of your nose, and the straightness (or curliness) of your hair depend on your genes. Not jeans the pants, but genes, the long strands of chemicals in your cells. Genes are like a blueprint for your body, and your cells follow the blueprint to build you. All living things have genes in their cells. You get your genes from your parents – half from your mom and half from your dad. Your parents got their genes from their parents, your grandparents. Living things pass down their genes from generation to generation. Genes from a mother’s egg cell mix with genes from a father’s sperm cell to make a complete set of plans for a baby. Baby humans, baby dogs, and baby plants all grow up to look like their parents because of genes.

Things can appear to be moving, when they really aren’t. Sometimes an object might seem to be at rest, even when it is in motion. It’s all relative. Relative motion, that is. How things appear to move depends on how you, or any observer, happens to be moving. So, if you’re on a bus looking out a window into another bus, and your bus begins to back up slowly, you may think the other bus is moving forward, when really it’s not moving at all. That’s motion in motion. It happens all around us all the time.

Things that fly need air. Even though we walk through it, breathe it, and sneeze it, air seems to be a whole bunch of nothing. But air is there, and it's powerful. Balloons inflate because air presses on the insides and outsides of the balloon. Air pressure in tires supports the weight of bikes, buses, trucks, cars, and planes. But air doesn't need to be inside something to exert pressure. Air that moves around pushes, too. What do birds, planes, kites, Frisbees, and helicopters have in common? They fly because moving air creates lift, or a push up. Airplane wings are shaped to push air down. The momentum of the air going down pushes wings up. Air above the wing gets going faster than the air underneath. Fast-moving air zips along, without pushing as hard side to side or up and down. The slow air pushes up from below harder than the fast air pushes down from above ... and you're airborne! Every flying thing, from the tiniest flying insect to the biggest airplane, us

About 70% of the Earth’s surface is covered in water, and almost all of that water has been around since the Earth formed billions and billions of years ago. That means a glass of water you drink today could be water that a dinosaur once sipped. Water is constantly recycled on Earth as rain, snow, sleet and hail. It makes its way in and out of oceans, lakes, streams, hail, and glaciers. Scientists call the recycling of water the water cycle (not that bad, huh?).

Friction is a force that slows moving things down and turns the moving energy into heat energy. When two things rub together, like your bike tires and the road, friction between them slows you down. There’s also friction in the metal parts of the wheel’s hub – at the center. There’s even friction between the fibers and rubber of the tires themselves as they flex and roll. That’s why you eventually stop rolling when you stop pedaling. Rough things make more friction than smooth things. Rubber shoes on a clean wooden basketball floor create more friction than do hard metal skate blades on smooth ice.

Don’t panic, but germs are all around you. Germs are bacteria, viruses, protozoa, and fungi, very small one-celled organisms. Your skin keeps most of these organisms from ever getting into your body. If germs slip inside, your body has some powerful weapons to attack and destroy them. And not all germs are bad; there are good germs, too, like the ones that live in our stomach and intestines – our guts.

Each planet is different. They are all different sizes – Pluto’s the smallest, and Jupiter’s the biggest. They come in a variety of colors – Mars is covered with rust, so it looks red; the methane (cold natural gas) in the atmosphere of Uranus makes it look blue; and Saturn’s colorful rings are made of icy rock. As far as we know now, Earth is the only planet in our solar system that is home to living things.