Now consider the solar panels on a school roof. They take in sunlight all day.

Tomorrow the Sun shines on the panels again. Nature makes more sunlight every day.

Today the panels take in sunlight. Tomorrow the Sun shines again.

Now consider a river that turns the wheel inside a dam all year.

Rain and melting snow fill the river again, so the river keeps flowing. Nature makes more moving water with every rain.

Today the dam uses the river's moving water. After the next rain, the river is full again.

A dam across a river, with a long lake behind it.

Now consider the logs a family burns in its stove each winter.

In the forest, new trees grow big enough to cut in some years, about twenty.

Today the logs are burned. Some years later, new trees have grown big.

A wood stove burning logs, with a stack of split logs beside it.