Sensor
A part that detects something in the world — heat, movement, sound, light — and turns it into a signal a machine can understand. A thermostat has a sensor for temperature. A smoke alarm has one for smoke.
Signal
Any message sent from one place to another — a radio wave, a flashing light, a sound, a shape on a screen. An engineer's job is often to make sure the signal arrives clearly and on time, even when the world is making...
Span
The distance a bridge, roof, or beam covers between its supports. The longer the span, the harder the engineering — because every extra metre adds more load the structure has to hold up without bending too far.
Steam
Water that has been heated until it turns into a gas. At a volcano, steam rises from anywhere hot water meets hot rock — it's one of the clearest signs the ground underneath is not as quiet as it looks.
Sulphur
A bright yellow element that's very common around volcanoes. When sulphur burns or mixes with water, it makes sulphur dioxide — a gas that smells like struck matches and can make your eyes sting.