One sunny morning, Milo, a curious little boy woke up with a big idea. He wanted to explore the world around him and discover what everything was made of. Milo had heard from his wise old grandma that everything in the world is called matter—and matter is anything that has mass and takes up space. “Time to find out!” said Milo, as he put on his tiny explorer hat.

First, Milo found to a giant rock in the garden. He tried to push the rock, but it wouldn’t move. “This rock is so strong!” Milo said. Then, he poked it with his finger. The rock didn’t change its shape or size. “Aha!” Milo said. “This must be a solid. Solids have a fixed shape and a fixed volume, which means they don’t change easily. And no matter how hard I try, I can’t press it!” Milo wrote in his notebook: • Solid: Fixed shape, fixed size, and cannot be compressed.

Finally, Milo felt the wind blowing gently. He held up an empty balloon and blew into it. The balloon puffed up! “Wow!” Milo said. “The air can change its shape and size. When I squeeze the balloon, the air inside gets press!” Milo realized that air is a gas. It has no fixed shape, no fixed size, and it can be compressed. Milo wrote in his notebook: • Gas: No fixed shape, no fixed size, and can be compressed.

At the end of the day, Milo sat under a shady tree and looked at his notes. “Rocks, water, and air are all matter,” he said proudly. “Solids, liquids, and gases—they’re all around me!” Milo smiled, feeling like a real scientist. He closed his notebook and scampered home, ready to share his amazing adventure with his grandma.