Posts
At first people used their own strength to work the machines they built. Next they used animals. Then they found out how to use the power of the wind when it blows, and of water when it flows. They built machines to catch this power stores as engines to work their other machines. This power 'catchers' were the sails and waterwheels which drove the mills.
Soon people found out how to make steam work their engines. Steam engines were very powerful and could be used anywhere to drive bigger and better machines. Some steam engines were use in the first cars. But today our cars have a much more powerful engine, the petrol engine. It uses petrol as fuel. The engine uses the energy from burning petrol to turn the car wheels.
The petrol engine has hundreds of different parts. There are several pistons and cylinders. The petrol burns in the tops of the cylinders and make hot gases. The hot gases push the pistons down. This movement makes a rod, or shaft, turn. Then gearwheels and other shafts carry the movement to the wheels.
We use other kinds of engines to turn the machines that make our electricity. One spins when water flows through it and is called a water turbine.
