'Pressure applied to a confined fluid is transmitted equally and undiminished in all directions.' This is:

Pascal's law, also called the principle of transmission of fluid pressure, was stated by the French mathematician and physicist Blaise Pascal in 1653. It states that when pressure is applied at any point in a confined (enclosed) fluid at rest, the pressure is transmitted equally and without loss to every part of the fluid and to the walls of the container.

Pascal's law is the basis of hydraulic machines. In a hydraulic system, two cylinders of different sizes, each with a piston, are connected and filled with a liquid such as oil. When a small force is applied to the small piston, it creates a pressure in the liquid. This same pressure acts on the large piston. Since force = pressure × area, the force on the larger piston is much greater. In this way, a small force can lift a very heavy load. This is called force multiplication.

Applications of Pascal's law:

• Hydraulic lift, used in car service stations to lift vehicles.
• Hydraulic brakes in cars, buses and trucks, in which pressing the brake pedal transmits pressure through brake fluid to all wheels equally.
• Hydraulic press, used to compress cotton bales and make metal sheets.
• Hydraulic jacks, used to lift vehicles.
• Excavators, cranes and dentists' and barbers' chairs.

The SI unit of pressure, the pascal (Pa), equal to one newton per square metre, is named after him. Blaise Pascal also invented one of the first mechanical calculators, the "Pascaline", in 1642, and contributed to probability theory and mathematics (Pascal's triangle).

Related facts: pressure in a liquid at rest increases with depth (P = hρg), and it is the same at all points at the same depth. This is why dams are built thicker at the bottom.

Why not the other options?

• ✗Archimedes' principle explains buoyancy (upthrust).
• ✗Bernoulli's principle relates pressure and speed of a moving fluid.
• ✗Boyle's law relates the pressure and volume of a gas at constant temperature.