Question

The Galileo thermometer shown in the photograph is based on the dependence of density on temperature. The liquid in the outer cylinder and the liquid in the partially filled floating glass balls are the same except that a colored dye has been added to the liquid in the balls. Explain how the Galileo thermometer works.

Answer 1

Notice that the liquid does not fill each of the floating glass balls. The quantity of liquid in each glass ball is sufficient to give each ball a slightly different density. Note that the density of the glass ball is determined by the density of the liquid, the density of the glass (greater than the liquid’s density), and the density of the air. Since the density of the liquid in the cylinder varies slightly with temperature—the liquid’s volume increases as temperature goes up, but its mass does not change, ergo, different balls will be buoyant at different temperatures.

Liquid volume in glass balls varies, giving different densities due to liquid, glass, and air. Temperature affects buoyancy.