Little Thunder woke up to a sparkly paddock. Every blade of grass was white and crunchy.

"The grass has turned into sugar!" he shouted.

Suzy trotted over, her breath puffing out in little clouds. "That's frost. It's water that froze overnight."

"But it didn't rain," said Little Thunder.

"The water came from the air," said Spike. "Air has invisible water in it, called water vapour. That's a gas. When the night gets very cold, the vapour freezes onto the grass and turns straight into ice."

Little Thunder tapped a frosty leaf. "So ice is a solid."

"Right," said Suzy. "The tiny particles in ice are packed close together and locked in place. They can only wiggle."

The sun climbed higher. Soon, the frost began to melt, and drops of water ran down the grass.

"Now it's a liquid," said Spike. "The particles warmed up and started sliding past each other. That's why water can flow and take the shape of any container."

Madrid the cow licked a wet leaf. "And by lunchtime, it'll all be gone."

"Where does it go?" asked Little Thunder.

"Back into the air," said Suzy. "The sun heats the water so much that the particles zoom apart and fly off as a gas. That's evaporation. It's the same reason puddles dry up."

Little Thunder thought hard. "So water goes round and round. Gas, solid, liquid, then gas again!"

"Exactly," said Spike. "Solid, liquid and gas are called the three states of matter."

At lunchtime, Little Thunder checked the paddock. The grass was dry and green. Not a drop of water left.

"It's like magic," he said.

"It's science," said Suzy. "But it is pretty magic."