Fluid

A fluid is a substance that can flow: both liquids and gases are fluids. An object falling through a fluid experiences resistance to its motion, called drag. In air, this is usually called air resistance.

Sound travels through a metal rod so quickly that timing its journey with a handheld stopwatch is unsuitable. This core practical investigates how to measure wave speed, frequency and wavelength in a fluid and a solid, and why different equipment suits each measurement.