Is the process of burning fuel?

Is a chemical reaction that produces energy?

In an ______________________ engine, fuel is burned outside the engine.

___________ , ______________, and____________ are three kinds of fuel used to produce steam.

When the burning of fuel takes place inside an engine, the engine uses _______________________

_____________ turbines are also used to make electricity.

The _______________________ brothers observed pieces of burning paper rise upward above fire.

The main part of a balloon is called the ________________ .

Large, modern hot-air balloons are made of _______________