What is the significance of density

This is why even small rocks sink while wooden objects, even large logs, float. As we have discovered more about the concept of density , we the science community have learned to harness this knowledge for our own use. One of the most readily recognized uses of the concept of density is the modern invention: the submarine.

Steel is certainly more dense than water. One could ask the question how a submarine that weighs several tons would be able to float. A submarine takes advantage of air space found within it.

The ship's total density is less than water; therefore, it will remain afloat. The captain of the sub opens the hull to allow water in and causes the sub to submerge into the water. Once the water is released or pumped out , the submarine comes back to the surface. If it is more dense than the fluid, it will sink. This concept explains why some objects float on water while others sink. For example, most types of wood float on water because they are less dense ; steel, by comparison, sinks because it is denser than water.

How, then, can large steel cruise ships stay afloat? Large ships have a tremendous amount of space in them that is filled with air think about it: cabins, movie theaters, onboard casinos, etc.

While steel is denser than water, air is a lot less dense than water see Table 1. Metal ships can float because their total density — steel plus air — is less than that of the water that they float on. When the metal hull of a ship is breached, like when the Titanic struck an iceberg, water rushes in and replaces the air in the ship's hull.

As a result, the total density of the ship changes and causes the ship to sink. The concept of changing density is commonly employed in another type of vessel, a submarine. A submarine has a constant volume but it can vary its mass by taking in water into its ballast tanks. When water is taken into the ballast tanks, the mass and thus density of the submarine increases and the submarine attains negative buoyancy that allows it to submerge into the ocean depths. Conversely, when water is released from the ballast tanks the vessel's density decreases allowing it to surface.

Mixing materials of different densities has predictable results. Have you ever noticed what happens to a bottle of oil and vinegar salad dressing when it is allowed to sit still after it has been shaken? The oil will rise to the top and the vinegar will settle to the bottom of the bottle.

This happens because oil is less dense than vinegar. When materials of different densities are put in contact with one another, their relative densities will determine how they order themselves. This phenomenon, where materials layer themselves according to their density , is called superposition. The density of a material is strongly connected to other intensive properties, particularly temperature see our Temperature module.

Many materials expand when they are heated. Because a material that expands takes up a larger volume , its density decreases. This phenomenon occurs in all forms of matter: for example, solids , liquids , and gases. The tightly coupled relationship between density and temperature explains how hot air balloons work. Concentration determination is also possible if a mixture contains several components and only one of them varies while all other ingredients are constant.

In industries like the petrochemical industry the density of a product is a very important characterization number or quality parameter. Norms including the ASTM norm define a certain density for every product, e. Using density measurement these materials can be characterized and the quality of each product can be defined.

Density is also used in general as a standard parameter in professional academic research to get to know the special physical behavior of a product. In petrochemistry, scientists are used to measuring the density of gasoline at different pressures and temperatures in the laboratory to find out how it will react once injected into an engine.

Another important application of density measurement is quality control, not only in the soft drink or petrochemical industry, but also in the production of alcoholic beverages beer, spirits, wine , fuels including biodiesel and bioethanol , cosmetics, personal care products, pharmaceuticals, and many more. Whereas some products are quantified by their weight, others are filled, paid, or even taxed by their volume.

A well-proven procedure is to measure the weight of a fluid product with a balance, followed by calculating the filling volume by using the density of the sample. This procedure is applied wherever the measurement of volumes is not possible, e. Density measurement is used to specify and describe a pure substance, but also determines concentrations of binary mixtures and therefore gives information about the composition of mixtures. It is, for example, useful during quality control or helps determine the filling volume during the bottling of a product.

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