According to renowned mathematician Archimedes, any object that is submerged in fluid is buoyed up by a force equal to the fluid that was displaced by the object. This simple principle explains why ships float in the ocean and hot air balloons rise into the sky.
A popular story relates how Archimedes used his principle to assist King Hieron II of Syracuse in identifying a deception against him. The king had ordered a crown to be made from solid gold, but he suspected that the maker had used other materials. Archimedes submerged the crown in water and measured the displacement. He then submerged equal weights of silver and gold into the water and monitored the displacement. The crown displaced more water than the gold but less than the silver, proving that it had been made of a mixture of the materials.
Recreate this experiment with items of various densities that have identical weights. Beads are ideal for this; they come in a variety of shapes and sizes and can be easily weighed for consistency.
Use several beakers with mL measuring marks on the side. Fill each beaker with an equal amount of water. Insert a different bead into each beaker. Use beads made from glass, wood, pewter, ceramic, plastic and rock. Measure the fluid displaced by each bead by subtracting the original volume of the water from the new volume created by the bead. Test some beads that are made from multiple materials and attempt to determine what the materials are based on the density tests.
The Archimedes Principle also deals with buoyancy. The law states that the buoyant force of the object is equal to the weight of the fluid displaced by the object. Experiment with buoyancy by creating different shapes from materials of a consistent weight and density.
Cut squares from a sheet of tin foil. Make sure that each square has identical dimensions. Tightly crumble one square into a compact ball. Eliminate as much air as possible from the ball to increase density. Fashion another square into a canoe shape. Fold one into a cube. Leave another flat. Experiment with different shapes.
Fill a tub with water. Place each object in the tub and determine its buoyancy. The canoe shape will float best. The ball will sink quickly. This is because the density of each object is different, even though the objects were created from the same exact materials.
The density of the fluid that the object is placed in will affect the buoyancy of the object. Just as people float easier in salt water than fresh water, objects will exhibit different degrees of buoyancy when immersed in different fluids.
Use two items with identical weights, such as a heavy bouncy ball and a toy boat. Fill different tubs or pails with various liquids, such as vegetable oil, pancake syrup, salt water and fresh water.
Gases are also fluids, and therefore are subject to the conditions of the Archimedes Principle. Test a balloon and a feather in a bucket of air to see what happens.
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