Julius Sumner Miller: Lesson 14 - Pascal's Principle - The Properties of Liquids

MATTER as we know it exists in three familiar "states": Solid-Liquid-Gas. Liquids have strange and wonderful properties one of these being incompressibiiity - they cannot be squeezed together very much. We show this enchanting business in a number of DEMONSTRATIONS. A - PASCAL'S PARADOX: Three glass vessels have different shapes but the same base. We fill these to the same depth with water. And very strangely they have the same pressure on the bottom and the same force on the bottom. Pressure we define as a Force per unit area - that is P = F/A. B - The Hydraulic Press utilizes the dramatic property of the incompressibiiity of liquids and Pascal's Principle which says: A force communicated to a liquid is "felt" without loss in all parts of the liquid. The press is worked by a lever so this machine is a Compound Machine and it has enormous Mechanical Advantage. C - A hypodermic needle has a very tiny point - a point of small area. If we push the piston with the thumb with a force say of ONE pound and the point has an area of ONE THOUSANDTH of a square inch we have at the point end a PRESSURE of ONE THOUSAND POUNDS PER SQUARE INCH. No wonder the needle goes in! D - We show an array of demonstrations of a simple ordinary sort which point up the beauty of these properties of liquids: 1 - We squeeze a flask equipped with a glass tube; the liquid goes UP and it goes DOWN. The glass is highly ELASTIC and the water is highly incompressible. 2 - The Cartesian Diver: The water is incompressible; the air IN the Diver very compressible. 3 - A flask filled COMPLETELY with water can be broken apart by a sharp blow on the stopper. WHY? The water is incompressible. 4 - A flask filled COMPLETELY with water can be used as a hammer to drive nails. WHY? The water is highly incompressible. E - A tin can is filled with water. The can has a TINY hole in the side near the bottom. With the stopper IN the water does not run out! Pull out the stopper and the water runs out! What holds the water IN? Answer: Atmospheric Pressure. F - A U-Tube has mercury in it to a certain level. We add water to one arm. The mercury falls in that arm and rises in the other. A measure of the mercury and water columns reveals a wonderful thing: The ratio comes out to be 13.6 - which is the specific gravity of mercury. We show a picture of Blaise Pascal - that genius of the 17th century who lived a very short life (1623-1662) but one filled with drama. He died as is said -with seven-fold immortality: as a mathematician - a physicist - an inventor -chief creator of his nation's great prose - a theologian - a philosopher - and a fanatic. His sister wrote a biography of him.