Buoyancy Explorer
Laboratory
Find out more about Buoyancy Explorer
What’s behind the Buoyancy Explorer
The Buoyancy Explorer contains density information for 8 liquids and 12 solids. Density is expressed in grams per cubic centimeter (g/cm³). You can predict whether a solid will sink or float in a given liquid by comparing their densities. If the solid is denser than the liquid, such as granite in water or tar in ethanol, it will sink. If the solid is less dense than the liquid, such as pine in water or iron in mercury, it will float.
For floating objects, the greater the difference between the density of the liquid and the density of the solid, the higher it will float. For example, balsa floats higher in water than oak does. Aluminum floats higher in mercury than in bromine.
When you use the Buoyancy Explorer, you can predict how high an object will float by comparing the density of the object with the density of the liquid it is in. For example, oak has a density of 0.75 and water has a density of 1.0. A volume of water three-quarters the size of the block has the same mass as the block. The block sinks into the water until it has displaced that volume of water. Three-quarters of the block is below the waterline, and one-quarter is above it.
Balsa has a density of 0.125 or one-eighth that of water. It floats such that seven-eighths of the block is above water and one-eighth is below.
The heights of the blocks in the Buoyancy Explorer are marked in eighths so you can check this for yourself. The numbers for most of the combinations do not work out as neatly as the two examples above, but you can calculate what portions of a block should be above and below the surface of a given liquid.
For example, the density of granite is about one-fifth that of mercury (2.7 / 13.55 = 0.20 = 1/5). You will see that the granite block floats approximately one-fifth below the surface of mercury and four-fifths above it.
Try other combinations.Here are the data we have used in the Buoyancy Explorer:
| Liquid | Density (g/cm³) | |
|
water olive oil ethanol corn syrup honey bromine sea water mercury |
1 0.918 0.79 1.39 1.43 3.12 1.022 13.55 |
|
| Solid | Density (g/cm³) | |
|
balsa ebony oak pine marble granite aluminum gold iron ice tar butter |
0.125 1.22 0.75 0.425 1.918 2.7 2.7 19.3 7.87 0.917 1.02 0.86 |
(The density information came from the CRC Handbook of Chemistry and Physics [CRC Press, 85th ed., 2004].)
Density of liquids varies somewhat with temperature. These figures are approximately correct at room temperature.
Some of the substances on our list, for example the four kinds of wood, can vary in density. We are using a figure in the middle of the range given in the CRC Handbook. Seawater also varies in density. The number we use here is for water at middle latitudes in the open ocean.
