Stand very still. You may think you are not moving, but the ground may be moving ever so slightly under your feet. The ground you are standing on is part of Earth’s crust. The crust is the solid surface or outer, rocky layer of Earth. Pieces of Earth’s crust are always slowly slipping and sliding around. The idea that pieces of Earth’s crust move is called the theory of plate tectonics.

The sound of an orchestra playing is a thrilling experience. An orchestra is a group of musicians who play musical instruments. Some orchestras have more than 100 musicians. Yet when they play together, the orchestra sounds like one mighty musical instrument.

Try to jump as high as you can. Bend your knees. Now jump! No matter how hard you try, or how high you jump, you always come back down again.
Something called gravity pulls you back down. Gravity holds you down on Earth. Without gravity, you would fly off into space. You would jump up and just keep on going. That might sound like fun, but you could not live very high up. For one thing, you need to breathe air. The higher you go, the less air there is. You need gravity to keep you down on Earth.

Remember Mary’s little lamb? It followed her everywhere. Lambs follow their mothers. If a newborn lamb loses its mother, it will form a bond with a human being who adopts it. Just like Mary’s lamb, it will try to tag after its human parent. Lambs are baby sheep.

What is love? What is truth? What is justice? Socrates, a philosopher in ancient Greece, asked big questions like these and tried to make people think.
Socrates was born in Athens, Greece, in 469 bc. He devoted his life to philosophy. He taught students, made speeches, and debated with anyone who would listen to him.

Imagine sticking your nose in the air and sniffing the smell of a hamburger cooking a mile away. Some bears can do just that. Bears have a keen sense of smell. They use this sense to help them find food. Bears are meat eaters, or carnivores. But most bears also eat fruits, nuts, and other foods. Bears live in North America, South America, Europe, and Asia. They do not live in Africa, Australia, or Antarctica.

A woman grips a long, slender club and stares down at a small, white ball on the ground. She swings the club back and then forward, striking the ball with a loud CRACK! The ball launches into the distance and comes to rest down a narrow stretch of grass.