Copyright © 2007 Dorling Kindersley
Vehicles use engines of different kinds to move people and cargo from place to place. Most cars and motorbikes have petrol engines, but vans and trucks use larger diesel engines. A diesel engine produces more power than a petrol engine by compressing the air and fuel much more. Petrol and diesel engines produce large amounts of pollution. ELECTRIC CARS are less polluting.
Trucks have big diesel engines that produce more power than a car engine, but they also use more fuel and produce more pollution. A truck is heavier and moves with more momentum (force) than a car travelling at the same speed. This is why a truck needs much more powerful brakes than a car and takes a longer distance to come to a stop.
Electric cars use batteries or fuel cells instead of engines and petrol. Batteries have to be charged up every so often, from the mains or from an engine, and the car then runs until the batteries are flat. Fuel cells work in a different way. Like an engine, a fuel cell takes in a steady supply of fuel, usually hydrogen gas. Like a battery, it produces a constant stream of electricity that powers an electric motor.
The world’s fastest solar-powered car, Nuna II, has a top speed of 160 kph (100 mph). It is built in plastic and covered in solar panels. These convert the Sun’s energy into electricity and store it in batteries, so the car can also drive in the shade. The body, solar panels, and batteries were originally developed for spacecraft.
Petrol engines are good for driving at constant, higher speeds on open roads. Electric motors are good for stop-start driving in city centres. They have lower top speeds than petrol engines. Hybrid cars have both a petrol engine and an electric motor. The car automatically switches between the two to suit varying traffic conditions.