Atmospheric pressure. Torricelli’s experiment and Pascal’s Principle.

Concept of Pressure

In the first of our online atmospheric pressure measurement simulations, it is possible to observe how the pressure that an object exerts on its base changes when the weight of the object or its contact surface changes.

Torricelli’s experiment

Torricelli’s experiment, performed in 1643, proved the existence of atmospheric pressure. Torricelli filled a glass tube about one meter high with mercury, sealed it and inverted it in a vessel also containing mercury. He observed that the mercury in the tube descended, leaving an empty space at the top, and stabilized at a height of about 76 cm. This phenomenon occurred because the atmospheric pressure pushed the mercury in the vessel upward, balancing the column of mercury in the tube. This experiment led to the invention of the first instrument for measuring atmospheric pressure, the mercury barometer.

Drag the mercury tube into the vessel and see what happens to its level depending on the atmospheric pressure of the planet.

Pascal’s principle

Pascal’s Principle states that a change in pressure applied to an incompressible fluid at equilibrium within a closed vessel is transmitted uniformly in all directions and to all points in the fluid. Pascal’s Principle has a multitude of practical applications in all kinds of hydraulic devices such as presses, brakes, elevators, etc.

In the last of our online atmospheric pressure measurement simulations, you can see how the equilibrium point varies in two connected columns of fluid when the radii of the tubes change.