Pressure measurement is the measurement of an applied force by a fluid on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure mechanically are called pressure gauges, vacuum gauges or compound gauges. The widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.
Example of the widely used Bourdon pressure gauge
Checking tire pressure with a spring and piston tire-pressure gauge
Natural gas pressure gauge
silicon piezoresistive pressure sensors
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a nearly constant volume independent of pressure. It is one of the four fundamental states of matter, and is the only state with a definite volume but no fixed shape.
The formation of a spherical droplet of liquid water minimizes the surface area, which is the natural result of surface tension in liquids.
A lava lamp contains two immiscible liquids (a molten wax and a watery solution) which add movement due to convection. In addition to the top surface, surfaces also form between the liquids, requiring a tension breaker to recombine the wax droplets at the bottom.
Cavitation in water from a boat propeller
Surface waves in water
