Things That Float or Sink in Water

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Things That Float or Sink
Whether something floats or sinks depends on its density and its buoyancy.

Identifying things that float or sink in water is a common science assignment. The project is straightforward enough for young children, but predicting whether a substance or object floats can become complicated because it involves both the density of the material and the buoyancy of an object. For example, ice floats on water. Steel is dense, so it typically sinks, yet ships made of steel sail on the seas every day.

Here is a list of substances that float or sink on water, based on density, and a look a how buoyancy lets even dense materials float.

List of Things That Float or Sink on Water (Density)

Density is the mass per unit of volume of a substance. The more mass there is in a volume, the higher the density. The density of water is about 1 gram per milliliter (g/ml) or 1 gram per cubic centimeter (g/cm3). So, things that are less dense than water float on it, while substances that are more dense than water sink in it. For numerical values, consult a list of densities of common substances. Otherwise, the list of things that float are all materials with a density less than 1 g/ml, while the list of things that sink all have a density greater than 1 g/ml.

List of Things That Float

  • All gases: Air, oxygen, hydrogen, nitrogen, carbon dioxide and other gases float on water. Even the densest gas, tungsten hexafluoride, has a density of 0.0124 g/ml and floats on water.
  • Ice
  • Oil
  • Gasoline
  • Alcohol
  • Lithium metal
  • Sodium metal
  • Wood
  • Cork
  • Plastic
  • Rotten eggs

List of Things That Sink

  • Dishwashing liquid
  • Milk
  • Blood
  • Corn syrup
  • Heavy water
  • Heavy water ice cubes
  • Honey
  • Shampoo
  • Fresh eggs
  • Coal
  • Concrete
  • Magnesium metal
  • Aluminum foil
  • Diamond
  • Steel
  • Iron
  • Granite
  • Lead
  • Steel
  • Brass
  • Bronze
  • Gold
  • A black hole

Does Poop Float or Sink?

Human feces (poop) either sink or float, depending on a few different factors. Mostly, poop is denser than water and sinks. However, it floats if a person’s diet is high in fiber or the stool contains a lot of gas or fat. While not necessarily indicative of a medical condition, floating poop can be indicative of an infection, pancreatitis, or irritable bowel syndrome.

Buoyancy

Even a dense object floats its shape gives it buoyancy. Buoyancy is the upward force exerted on an object submerged in a fluid (liquid or gas) that opposes the weight of the object. This force is due to the pressure difference between the top and bottom of the object, which creates a net upward force.

According to Archimedes’ principle, the buoyant force on an object equals the weight of the fluid displaced by the object. If the weight of the fluid displaced is greater than the weight of the object, the object floats. If the weight of the fluid displaced is less than the weight of the object, the object sinks.

Note that it does not matter how much water is below an object (assuming it is not touching the bottom). An object floats equally well in shallow water as in deep water. Also note that adding more weight to a floating object changes the balance of forces. So, if you pile enough mass onto a floating object, it eventually sinks.

A good example of a dense object that floats is a metal ship. Despite being much heavier than water, steel cargo ships and tankers float because the shape of the hull displaces a large volume of water, creating a buoyant force that supports their weight.

Prove It For Yourself

While it’s counterintuitive that heavy objects float if they displace enough water, it’s easy to prove it for yourself. Take a sheet of aluminum foil and crush it tightly into a ball. It sinks if you throw it into a bucket of water because aluminum is more dense than water. But, if you fold up the edges of a sheet of foil to form a makeshift boat, the aluminum floats.

Common Misconceptions About Floating

There are several common misconceptions about how floating works. The following statements are false:

  1. Light objects float and heavy objects sink, regardless of their size or shape.
  2. A floating object is completely above the surface of the liquid.
  3. Objects only float because they contain trapped air.
  4. Objects float better in deep water than in shallow water.

References

  • Bolz, Ray E.; Tuve, George L., eds. (1970). “§1.3 Solids—Metals: Table 1-59 Metals and Alloys—Miscellaneous Properties”. CRC Handbook of tables for Applied Engineering Science (2nd ed.). CRC Press. ISBN 9781315214092.
  • Lima, Fábio M. S. (2014). “A downward buoyant force experiment”. Revista Brasileira de Ensino de Fisica. 36 (2): 2309. doi:10.1590/S1806-11172014000200009
  • OECD (2012). “Test No. 109: Density of Liquids and Solids”. OECD Guidelines for the Testing of Chemicals, Section 1. ISBN 9789264123298. doi:10.1787/9789264123298-en
  • Serway, Raymond; Jewett, John (2005). Principles of Physics: A Calculus-Based Text. Cengage Learning. ISBN 0-534-49143-X.