Moving

It’s an old adage that travel broadens the mind. Moving around enables us to meet new people and make new friends, experience new cultures and new sights and find complete new perspectives on life.

For millennia we relied on walking and running. We searched for food and followed the seasons. We would have dragged large objects on a platform with smoothed runners – a sledge. Wheels would have made life much easier – from around 3500 BC. Moving around began to range from walking, running, riding horseback, wagons, rowing and sailing. Eventually people settled down to farm. The first evidence of humans getting about by riding horses dates from around 3,500 BC – about the same time as the first wheels of solid wood.

People wanted to find a way of moving themselves – it eventually came in the form of a velocipede – pedal power. The story of the evolution of the bicycle is exemplary of the ways in which we collectively engineer inventions. It started around 1817 when German Karl von Drais had the idea of building his draisine (dandy-horse). It was the archetype for a bicycle. The progress was inexorable to the sophisticated lightweight machine on which Chris Froome won his third Tour de France in 2016.

When a solid structure moves, say an aeroplane, ship or car, the separate parts stay together and move together – they obviously do not fly apart or accelerate away from each other. So the parts of a moving structure remain connected by internal forces in a state of dynamic equilibrium.

Samuel Morland in the 17th century experimented with the explosive power of chemicals when he tried to use gunpowder to make a vacuum to suck in water to make a water pump. The very practical need to pump water from mines prompted Thomas Savery in 1702 to build his ‘Miner’s Friend’ – an engine to raise water by the ‘impellent force of fire’. This first steam engine had no piston. Thomas Newcomen used the same idea as Savery, a vacuum from condensed steam, but he used it to pull a piston down a cylinder. The piston was linked to the end of a timber beam which rotated about a central pin. The other slightly heavier end of the beam was connected to a pump within the mine water. As the piston rose and fell, so the beam rotated and the pump rose and fell – bringing water out of the mine. In 1765 James Watt improved Newcomen’s engine by incorporating a separate condenser and then returning the warm condensed water to the boiler. In 1803-4 Richard Trevithick built an engine with much higher steam pressures  and used it to power a locomotive that ran 9 miles from ironworks at Penydarren to the Merthyr-Cardiff canal in South Wales. That presaged the railway age in which our means of moving around changed dramatically. The railway network flourished between 1830 and 1870.

Engines that create useful work from a difference in temperature are called heat engines. An energy source (e.g. chemical or nuclear) creates heat (through combustion) which does work (mechanical or electrical). The science of understanding and designing them is called thermodynamics.

The piston steam engine is an external combustion heat engine since the heat source is external to the cylinder. Cars and trucks have internal combustion engines (IC) because the fuel (hydrocarbons such as petrol – USA gas – and diesel) combusts inside the engine.The two main types of IC are spark ignition engines and Diesel engines. Spark ignition engines work on a thermodynamic cycle – the Otto cycle – named after its German inventor Nicolaus August Otto who patented it in 1876.

Turbines power much of our modern machinery. A turbine takes energy from fluid flow to do useful work. Examples of turbines are waterwheels, windmills (old and new), hydroelectric turbines, tidal energy convertors and steam-turbines to generate electricity and jet engines or gas-turbines. A gas turbine jet engine has the same four stages as an internal combustion piston engine. It is however much more elegant because rather than happening intermittently, the stages occur continuously and are mounted on a single shaft. The pressure and temperature in a piston engine changes quite dramatically with time whilst in a turbine both the pressure and temperature remain constant at steady speeds at given locations in the engine. The gas turbine is a very clever way of manipulating the pressure, volume, velocity and temperature of gas to create the thrust that propels the aircraft. First air is taken in (sucked), then it is compressed (squeezed), the fuel burnt (bang) and the mix is exhausted (blown) out through a turbine. The engine is a working example of Newton’s third law of motion – that for every action there is an equal and opposite reaction.