Your body, your house, your dog, the Earth: all these things are made of matter. Matter is the name that scientists give to all of the substances in the universe.

Is water a kind of matter? Yes, water is a kind of matter called a liquid. Other kinds of liquid include milk and the gasoline we pump into our cars. Water is by far the most common form of liquid on Earth, though — most of the Earth’s surface is covered by water.

Wave your hand through the air. You can feel the air wooshing past your hand. Is the air made of matter? Yes, air is a kind of matter called a gas.  Other kinds of gasses include carbon dioxide (which plants breathe) and helium (which is used to make toy balloons float).

Most of the things you can see or touch are made of matter. Even things you can’t see (like the air) are made of matter. Are there things in this world that aren’t made of matter? Yes: some things are made of energy, which is different than matter. There are lots of ways to see energy in the world. Sunlight is a kind of energy. When a bolt of lightning hits the Earth during a storm, that’s energy too.

People and most animals have tongues. Your tongue is good for three things:

• Helping you eat food
• Helping you taste food
• Making funny faces

We taste food with our tongues to see if the food is good to eat or not.

Did you ever notice that your tongue is bumpy? The bumps you feel on your tongue are called taste buds. They’re the part of the tongue that lets you taste things.

You have about ten thousand taste buds on your tongue. There are different kinds of taste buds for different kinds of tastes: sweet, salty, savory, bitter and sour.

When you take in a breath, what happens? If you take a big breath, you can feel air going into your body through your mouth. But why do we breathe? We breathe because our bodies need something in the air called oxygen. Oxygen is like food for our blood. You can’t see oxygen, but it’s there in the air, and people and animals need it to live.

Your body changes oxygen into a different gas called carbon dioxide. Carbon dioxide is what comes out of your body when you breathe out. You breathe in oxygen, and you breathe out carbon dioxide.

Trees and plants don’t breathe oxygen as we do. They take in carbon dioxide and they put out oxygen — just the opposite of people and animals. So having lots of plants around is good for people and animals — plants and trees make the oxygen that we need to breathe.

You may be learning to write letters and numbers in school. But how did ancient people figure out writing, in the days before we had schools?

People didn’t always write. Cavemen didn’t write. People started writing about six thousand years ago. To keep track of information, people would make little marks in soft clay using a tool called a stylus. Over time, people began to agree on what the marks should mean.

Different people write things in different ways. In this picture you can see the Rosetta Stone, which is carved with ancient writings. The Rosetta Stone is important because it shows three different kinds of ancient writing. Scientists were able to figure out a lot about what the ancient writing meant by comparing the letters on the stone to information they knew about these ancient languages.

The Rosetta Stone was created more than 2,200 years ago and was discovered in the year 1799 in Egypt. It is currently stored at the British Museum in London.

Years ago, dinosaurs roamed the Earth. But while there are no dinosaurs alive today, there are creatures that are related to dinosaurs — reptiles such as snakes and alligators, as well as some fish, plants and other creatures.

We know that dinosaurs died out millions of years ago, but where did today’s reptiles come from?

The world was very different when the dinosaurs were alive — it was much hotter and wetter. Over time, the world changed and it became harder for dinosaurs to survive. Some scientists believe that an asteroid (a large rock from space) may have hit the earth in the time of the dinosaurs, causing the temperature to drop suddenly.

When big changes like this happen, some creatures are well suited to survive, and others aren’t. Creatures that are not well suited to survive in the world will die out. A creature that is well suited to survive will have lots of babies that will often be even better suited to survive.

After the earth cooled during the time of the dinosaurs, most dinosaurs died out. Those few who survived had babies who were smaller, smarter, and quicker. As time went on, those babies had babies of their own, and over the course of thousands of years, these creatures didn’t look like dinosaurs at all anymore. They had changed into new kinds of animals, and these animals were well suited to survive in the changed world.

All types of creatures change slowly over time. Scientists call this process evolution.

Here is a video from NASA, the American government agency that is responsible for the space shuttle and other rocket launches. The video shows the space shuttle’s solid boosters returning to earth. The solid boosters are two of the space shuttle’s gas tanks. When the space shuttle is high enough off the earth, the boosters break off from the space shuttle and land in the ocean. This video takes about five minutes to watch. It follows the boosters from the time the break away from the space shuttle to the time they splash down in the ocean. Be sure to watch all the way to the end to see a surprise.

A volcano is a special kind of mountain. Volcanos are special because they can erupt. When a volcano erupts, it can sent hot lava, steam, ash, and rocks into the air.

The heat from a volcano comes from deep within the earth. Many miles underground, the earth is hot. Rocks beneath the earth are so hot they turn into a liquid called lava. When a volcano erupts, the steam and ash is caused by lava that is forcing its way toward the surface of the earth.

We don’t find volcanos in every part of the world. In the United States, most of the volcanos are in Hawaii and Alaska. There are quite a few volcanos in Asian countries such as Japan. The largest active volcano in Europe is called Mount Etna, in Italy.

You don’t have to be worried about being hurt by a volcano. Volcanos erupt very rarely, and most volcanos don’t hurt anybody when they erupt.

Doctors know a lot about how to help people who are sick or injured. But how do they learn how to help people? It takes years of special schooling to learn how to be a doctor. In medical school, doctors learn about peoples’ health from books and classroom discussions, but they also learn by doing experiments, just like other scientists.

To really learn about what’s inside our bodies, student doctors sometimes cut up dead bodies. Bodies that are used by student doctors are called cadavers. Before they die, people sometimes give permission to medical schools to use their bodies to teach doctors. Cutting up a dead body may seem gross, but doctors become accustomed to it. Using cadavers is the best way for a doctor to learn what goes on inside our bodies.

You’ve probably noticed that sometimes when you cut yourself, blood comes out. But what is blood, and why does it come out when we cut ourselves?

Blood is made of many different parts. These parts of the blood are tiny — smaller than you can see. One part of blood is made of red blood cells which carry the air you breathe throughout your body. Red blood cells also give blood its red color.

You can see what blood cells look like under a microscope in the picture at right. (Because this picture was taken by a microscope, which makes tiny things look much larger, the cells look bigger than they do in real life.)

When you get a cut, sometimes tiny creatures that are too small to see can try to get inside your body through the cut. If some of these creatures get into your body, they can cause an infection, which makes the cut hurt a lot more. Your blood helps keep those bad creatures out. There’s another part of your blood, called white blood cells, which help keep the bad guys out of your body. Like red blood cells, white blood cells are also too tiny to see. The job of a white blood cell is to prevent bad creatures from coming into your body through a cut and infecting you.

Whenever you cut yourself, you should get help from an adult (like one of your parents or a teacher) to clean the cut and put a bandage on it.

Getting a cut is no fun, and you probably don’t like to see blood come out when you cut yourself, but remember that the blood is there for a good reason.

Have you ever seen a shooting star? Sometimes late at night you can see a streak of light blaze across the sky, as in the picture at right.

Is a shooting star really a star? Not really. Real stars (including our sun) are giant balls of fiery gas. Shooting stars are actually much smaller than real stars, and they’re made of rock or metal. They look like stars because they fly through the air so quickly that they become hot and glow. You can see how this works by rubbing your hands together. The same force that makes a meteor hot as it flies through the air is what makes your hands hot when you rub them together. This is called friction.

Scientists have a special name for shooting stars: they call them meteors.

You don’t have to worry about being hit by a meteor. Most meteors burn up before they hit the earth.