physical science

The diagram below shows the four steps in a four-stroke engine: 1. Intake: In this first stroke, the piston moves down and the intake valve at the top of the cylinder opens to allow air and fuel to enter the cylinder. 2. Compression: The piston moves back up and compresses the air/fuel mixture. 3. Combustion: The spark plug gives off a spark which causes an ignition and a controlled combustion of the air/fuel mixture. As a result, pressure is created which forces the piston back down. 4. Exhaust: The exhaust valve opens and the piston moves up, resulting in the exhaust gas being pushed out of the cylinder. This cycle repeats so the engine is able to produce power.