Convert petagram/liter [Pg/L] to milligram/centimeter³ [mg/cm³] • Density Converter • Mechanics • Compact Calculator • Online Unit Converters (2023)

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Overview

Density indicates how much of the mass of a substance fits in a given volume. The SI unit for density is kg/m³, but alternative measures are also used, like g/cm³ and kg/L, for example. In everyday life the equivalent units of g/cm³ and g/mL are most commonly used.

Factors Affecting Density

Density varies for substances depending on their temperature and pressure. Higher pressure causes the molecules of the substance to become packed more densely within the same volume, increasing the density. Increase in temperature, on the other hand, generally causes the molecules to become more spaced out, thus decreasing the density. This is not always true, however. For example, the density of ice is lower than that of water. When most other liquids solidify, the space between the molecules decreases. When water molecules freeze, the bonds within the molecules change intensity, and form a crystal. Space between molecules increases, volume of the water expands, and the density decreases. Expanded volume of ice is why water that freezes in the house pipes in winter may make the pipes burst.

Density of Water

When materials have higher density than that of water, they sink. Conversely, materials with lower density float. A good example is ice floating in a glass of water. This property is often used in daily life. In most cases hollow objects, made from more dense materials than water for structural reasons, contain air, which is less dense than water. This allows the vessel to float, as long as enough air is carried inside the cavity. In fishing, the weight is made from high density materials such as metals, to make sure that it brings the hook down into the water, instead of having it float at the surface, especially when the bait is low in density and does not sink well.

Oil is lower in density than water, so it floats. This property of oil allows for easier cleanups, when dealing with oil spills that frequently occur in the ocean and damage the marine ecosystem. The tendency of oil and fat to float above water is also helpful when cooking — we can remove the fat that floats in our soup, for example, to reduce the percentage of fat and the calories in the dish. This is especially easy if we refrigerate the soup until the fat solidifies. This is also easy to do on aspics.

When making cocktails or other similar drinks, the ingredients can be chosen based on their density to create layers. To make layers, a lower density liquid is poured slowly above the higher density ones. One can also use a glass stirrer as a guide for the liquid (not for stirring). If done carefully, this technique will prevent mixing, and create a colorful layered drink. It is also possible to do this when making jelly or aspics, although, if time permits, it is easier to refrigerate each layer separately and then pour the next layer on.

In some cases, however, this quality may not be desirable. For example, when the substances containing fat do not mix well with water, they may separate, such as in a poorly blended smoothie, thus making the taste and the look of the food less desirable.

Density of Salt Water

A cherry tomato is suspended on the “border” between the more dense salt water in the bottom, colored in pink, and the less dense fresh water at the top. The density of the tomato is less than that of the salt water, but more than the density of the fresh water — this is why they are suspended in the middle.

The density of water itself changes with the change of concentration of other substances mixed with water. Water in nature is not always found in its pure H₂O form, but is often mixed with other substances such as salt. Ocean water is a good example. For example, salt water in oceans has higher density than fresh water, which means that water with less salt in it floats in salt water. Of course it is difficult to see that with just water, but we can observe this property when we try to float in salt water. Our body consists of 45% to 75% of water, with higher percentage in children, and lower percentage in older and obese individuals. We also have at least 5 percent of body mass consisting of fat. This data is for very lean athletes — the majority of us have at least 10 percent of fat but usually up to 20 in the majority of healthy individuals, and 25 percent or more in overweight and obese individuals.

When we try floating in salt water and then in clear water, we will notice the difference — our body will float easier in salt water. The Dead Sea is famous for having the salt concentration about 7 times greater than that of the world’s oceans, which allows people to float in it without sinking. Even though people cannot sink below the water surface, caution must still be exercised when floating in the Dead Sea. Swallowing the water with such high content of salt causes a chemical burn that in severe cases has to be treated in the hospital.

Density of Air

Similar to water, objects that have lower density than air float. For example, helium’s density is 0.000178 g/cm³, compared to 0.001293 g/cm³ of air. Because helium’s density is lower, it floats in the air, as we can see by filling a balloon with helium and watch it rise up.

As the temperature of air rises, its density decreases. This is what makes air balloon rides possible. The hot air balloon in the archeological site of the ancient Mayan city of Teotihuacan in Mexico (pictured) is lifted up because the air inside it is heated above the temperature of the surrounding air, which, consequently, decreases the density inside the balloon envelope. As the balloons float above the pyramids, the cold morning air cools the air inside of them as well, and the operator has to use the heater to keep the air warm inside the balloon’s envelope.

Calculating Density

Pre-calculated density values are available for many substances under the standard conditions for temperature and pressure, which are 0 °C and 100 kPa. Sometimes, however, we might want to calculate the density by hand, especially if the calculations are not done under the standard conditions. To do this we can divide the mass by the volume, and we need to know these two values for the substance. We can measure the mass using a scale. The volume can be calculated based on the geometric shape of the object for simple solids, by using devices like a measuring cup or other measuring vessels for liquids and gases. If the shape of the solid is too complex for the geometry-based calculations, we can find its volume using the volume displacement method.

Volume Displacement

We can do these calculations for objects of complex shapes by pouring water in a measuring cup or a similar vessel and measuring this initial amount of water. We then submerge our irregularly shaped object under water completely and measure by what amount the water has been displaced. This displaced volume is equal to the volume of the submerged object — an observation supposedly formulated by Archimedes. Using this method is only possible with objects that do not absorb water or that cannot be damaged by water. We would not use it to measure a volume of a camera or an article of clothing, for example.

According to legend, truthfulness of which is debated, Archimedes was given a task by the king Hiero II of Syracuse to check if the crown that the king commissioned a goldsmith to make, was made of gold. The king suspected that the goldsmith substituted the gold, that the king gave him, by a cheaper alloy, profiting from the difference. Archimedes could determine this by calculating the density of the crown and comparing it to the density of gold, known at the time. Melting the crown was not a possibility, therefore he had to find a way to calculate the volume without altering its shape. The story has it that he wondered and puzzled about what to do, and a solution came to him when he took a bath and submerged himself in the water. He suddenly realized that he could measure the volume of any object by measuring how much water it displaces when fully submerged.

Substances with Voids

Some substances found in nature or manufactured are either hollow inside or are similar to liquids in their properties but consist of particles that are big enough to allow voids between them even if the substance is packed densely. Some examples of the latter include sand, salt, flour, grains, snow, and gravel. The void space can be filled with air, water, or other substances. It could also be empty, in which case there is vacuum in the space between particles. Density calculations for such substances can be done in bulk, including the void, or by estimating geometrically the volume of the void space and subtracting it from the total volume, if the particles have relatively uniform shape.

There are some substances that may be packed more loosely or more compactly and have more or less space between the particles, depending on how they were poured or packed to attain their current state. This makes density calculations for them more difficult, because it is harder to estimate the void volume.

Density of Common Substances

Density and Mass

In some industries, for example in aeronautics, it is paramount to use materials that are as light as possible. For the same volume, the lower the density of the material, the lower its mass. When the mass needs to stay low, materials with low density are used. For example, density of aluminum is about 2.7 g/cm³, while density of steel ranges between 7.75 to 8.05 g/cm³. This is why aluminum and its alloys are used for about 80% of the airframe of the aircraft.

Composite materials replace metal components in airplanes because they exhibit desirable physical properties including light weight and high elasticity. Propellers of this Bombardier Q400 are all composite.

Black Holes

Conversely, as the mass increases, so does the density. Black holes are an example of bodies with very high density because their mass is extremely large while the volume is negligibly small. Such conditions create an astronomical body which absorbs light and other objects, waves, and particles that are at a close enough distance to it — the largest of these are called supermassive black holes.

References

This article was written by Kateryna Yuri

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Online Unit Converters Mechanics

Mechanics

Mechanics is the branch of physics, which studies the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment.

Density Converter

The mass density or density of an object is a scalar value, which is equal to its mass per unit volume. In other words, density is the measure of the relative “heaviness” of different objects having a constant volume.

The SI unit for density is kilograms per cubic meter (kg/m³).

Using the Density Converter Converter

This online unit converter allows quick and accurate conversion between many units of measure, from one system to another. The Unit Conversion page provides a solution for engineers, translators, and for anyone whose activities require working with quantities measured in different units.

You can use this online converter to convert between several hundred units (including metric, British and American) in 76 categories, or several thousand pairs including acceleration, area, electrical, energy, force, length, light, mass, mass flow, density, specific volume, power, pressure, stress, temperature, time, torque, velocity, viscosity, volume and capacity, volume flow, and more.
Note: Integers (numbers without a decimal period or exponent notation) are considered accurate up to 15 digits and the maximum number of digits after the decimal point is 10.

In this calculator, E notation is used to represent numbers that are too small or too large. E notation is an alternative format of the scientific notation a · 10^x. For example: 1,103,000 = 1.103 · 10⁶ = 1.103E+6. Here E (from exponent) represents “· 10^”, that is “times ten raised to the power of”. E-notation is commonly used in calculators and by scientists, mathematicians and engineers.

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• Enter the value (for example, “15”) into the left From box.
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