All of the Year 7/8 children have been doing Passion Rotations during the past few weeks. They meet up a couple of times a week and get stuck into something they are passionate about. One of the rotations is Science - where the children have been making Putt-Putt boats.

A putt-putt boat is a type of steamboat which was named for the sound that the motor makes. The noise is caused by the boiler expanding and contracting rapidly whilst constantly being heated by a flame of some kind.

The motor works by (after the boiler and the two (or more) tubes leading out of it are filled with water) heating the boiler with a flame, in this case a birthday candle. This heats the water inside to the point where it is almost purely steam. This expands (obviously) and pushes water out of the tubes and boiler, creating a vacuum which sucks in water and the whole process repeats over and over again. This vacuum and then the lack of is the cause of the noise.

Steam engines are typically external combustion engines (external heat source, usually fire). This type of steam engine is incredibly simple with only one moving part. However, by having an open flame much of the heat is dissipated to the surrounding air, and not the boiler. This makes it less efficient than an internal combustion engine (internal heat source, usually fire)of the same power output.

This was written by Declan Farr.