Density and Buoyancy Concept

Demonstrations in Density and Buoyancy

Welch two-pan balance with two 250 mL beakers: left beaker contains a green-and-white superball, right beaker contains green-dyed water at about 150 mL

Buoyancy Balance

A floating superball displaces exactly its own weight in water, demonstrated directly on a two-pan balance. A bonus step shows that the displaced volume of water weighs the same as …
Three-panel photo: (left) brass bucket and cylinder hanging in air, scale reads ~23 N; (center) cylinder submerged in water, scale reads ~20 N; (right) brass bucket filled with water, scale returns to ~23 N

Archimedes' Principle, Bucket and Cylinder

Quantitative verification of Archimedes' Principle: submerging the brass cylinder reduces the scale reading by the buoyant force, and filling the matched bucket with the displaced water's weight restores the original …
Large dial spring scale (20 N, Sargent-Welch) hanging from horizontal rod on bench clamp stand, with brass crown suspended from the scale in air; Pyrex beaker of water on bench to the right

Archimedes' Principle, Crown

Demonstrates Archimedes' Principle by weighing a brass crown in air and in water. Students calculate the buoyant force and determine the crown's density, connecting to the classic legend of Archimedes …
Side-by-side photos: left shows a small brass cylinder with hook on an Ohaus Scout Pro scale reading 100.4 g; right shows the overflow cup on a wooden block with an empty collection beaker beneath its spout, scale reading 12.5 g

Archimedes' Principle, Overflow Cup

Measure the density of an irregular body heavier than water using an overflow cup. Weigh the test body, immerse it to collect the displaced water, and divide the two weights …
Wooden cylinder with horizontal colored bands sitting in a 1500 mL Pyrex beaker, fitting snugly; a graduated cylinder filled with red-brown colored water stands beside it

Battleship in a Bathtub

Buoyant force depends on the depth of displaced water, not the total volume of water in the container. A wooden cylinder floats in a snug-fitting beaker with only 40 mL …
Side-by-side photos of a tall clear acrylic cylinder filled with water, sealed with a neoprene membrane and band clamp. An inverted test tube with a paper clip chain hangs inside. Left: diver floating near the top with chain extended. Right: a hand presses down on the membrane and the diver has sunk lower.

Cartesian Diver

Pressing a neoprene membrane on a sealed water-filled cylinder compresses the air pocket in an inverted test tube diver, increasing its density and causing it to sink. Demonstrates the interplay …
U-tube mounted on a ring stand with clamps. Left arm contains yellow oil, right arm contains red-dyed water. The oil column is visibly taller than the water column. The U-bend at bottom is filled with red water.

U Tube with Water and Oil

Shows that hydrostatic pressure depends on both depth and density. Immiscible fluids in a U-tube reach equilibrium when the pressure at the interface is equal on both sides, so the …
Five glass hydrometers of various sizes laid out on a surface with a ruler for scale
Safety

Hydrometers

Hydrometers float at different levels in liquids of different densities, providing a direct, quantitative application of Archimedes' Principle. Students see how the equilibrium floating position depends on fluid density and …
Clear graduated bucket with two dark bowling balls in water: the lighter ball floats at the surface (partially submerged) and the heavier ball sits on the bottom

Density of Bowling Balls

Two bowling balls of the same size but different masses are weighed, their densities calculated, and then placed in water. The heavy ball (6.6 kg) sinks; the light ball (3.1 …
Tall clear cylindrical glass tank filled with water, with a red Coca-Cola can suspended upside-down at mid-depth by a paper clip chain trailing to the bottom

Neutral Buoyancy

A soda can attached to a paper clip chain achieves hydrostatic equilibrium at a specific depth in a water column. The chain creates a position-dependent weight, producing visible oscillations around …
Diet Pepsi floats at the surface while regular Pepsi sits on the bottom of a large beaker filled with water

Density Sodas

Identical-looking soda cans float or sink depending on their average density relative to water. Students see that small compositional differences — sugar vs. artificial sweeteners — produce dramatically different buoyancy …
Two hollow metal density balls -- one matte and one polished -- photographed on a dark surface

Density Balls

A density ball sinks in plain water but floats after adding salt, directly showing that an object's buoyancy depends on the relative densities of object and fluid. By carefully controlling …