Pascal’s law and its applications
The French scientist Blaise Pascal (1623–1662) formulated in 1653 the following law: an external pressure applied to a liquid or gas is transmitted unchanged to every point of the liquid or gas and equally in all directions. You can see it in a bottle of water or a closed rubber ball: wherever you press the ball, it swells equally on all sides. Solids transmit force only in the direction of the force, but liquids and gases transmit pressure in all directions because their molecules are mobile. Machines such as the hydraulic press, hydraulic brakes, car lifts and excavators are based on Pascal’s law. A hydraulic press has two connected cylinders with pistons of areas S₁ and S₂. As the pressures are equal, F₁ : S₁ = F₂ : S₂, so F₂ : F₁ = S₂ : S₁: the force gain equals the ratio of the areas.
“Syringe hydraulics”: connect two plastic syringes (thin and thick, with NO needle) with a water-filled tube; press one and watch the other move. Safety: use only syringes with the needle removed, work under adult supervision and wipe up spilled water.