Transport science: engines, electric vehicles and safety

A vehicle is an energy converter on wheels, and comparing engines means comparing how they convert stored energy into motion. A petrol or diesel engine burns fuel inside cylinders: the expanding hot gases push pistons, which turn a crankshaft and eventually the wheels. Only a fraction of the fuel's chemical energy becomes motion; much of the rest leaves as heat through the exhaust and cooling system. That waste heat is the main reason internal combustion engines are inefficient, and why their exhaust contains carbon dioxide and air pollutants that must be cleaned by catalytic converters and filters.

An electric vehicle works differently. A battery stores electrical energy chemically and releases it to an electric motor, which converts it into motion far more efficiently than a combustion engine, with no exhaust at the vehicle itself. Electric motors also allow regenerative braking: when the driver slows down, the motor runs in reverse as a generator, recovering some energy back into the battery instead of wasting it all as heat in the brakes. The environmental benefit of an electric vehicle therefore depends on how its electricity is generated — a grid powered by coal gives a smaller benefit than one powered by renewables — and on the energy and materials used to make the battery.

Safety in transport is applied physics. A moving vehicle has momentum, and in a crash that momentum must be removed quickly; the forces involved depend on how fast the vehicle stops. Seat belts, airbags, and crumple zones all work by extending the stopping time and spreading forces over a larger area, reducing the deceleration experienced by occupants. That is also why speed matters so much: because kinetic energy rises with the square of speed, a crash at higher speed involves far more energy to absorb, and why heavy vehicles need greater braking distances.

The future of transport is a systems question, not only a vehicle question. Electric buses and trains move many people with less energy per passenger than private cars; well-designed cities shorten trips so that walking and cycling become practical; and freight shifted to rail or water uses less fuel per tonne than road haulage. Fuels, batteries, roads, and rules interact: a cleaner vehicle on a congested road still wastes time and energy, and a fast train needs tracks, stations, and timetables to succeed. Transport science therefore spans engines, energy, safety, and planning.