The definition of density, which is scientifically referred to as the volumetric mass density, is the amount of a substance by mass per unit volume. It's understood to be the amount of a particular substance in a fixed measurement, which can be measured in a variety of different units.
The density of a substance changes depending on the temperature and pressure. Solids and liquids don't usually vary that much in their density depending on those factors;the change in density based on temperature or pressure can be dramatically different for gases sinceincreasing the pressure on an object decreases its volume, increasing its density. The correlation is also true that an increase in the temperature of a substance usually decreases its density by increasing its volume.
1. Oil and Water Don't Mix
It's a known fact that oil and water don't mix, but what many people may not know is that the density of oil is what makes it float on top of water. In the kitchen, oil and vinegar don't mix either, and you may have seen a bottle of salad dressing with a slimy-looking layer on top. The oil is less dense than the vinegar, too. But a very serious, real-world application of oil's lighter density than water is in the ocean in the event of an oil spill. We haven't quite perfected the technology, but scientists have already developed clean-up systems that scrape or soak that top layer of oil off the ocean's surface in the event of an oil spill. That oil is still wasted and can cause lasting damage to the environment, but scientists are able to reduce the harmful impacts by removing much of that layer from the top.
2. Helium Balloons
Helium balloons lend a festive air to parties by floating above the ground, a phenomenon which occurs due to helium's density. Since it is less dense than the air around it, the balloon floats. This characteristic is important in weather balloons and at one time was important in dirigible and blimp flights. While helium is the second most abundant element in the universe, its density makes it pretty rare on Earth. We actually dig it out of the ground rather than extract it from the atmosphere.
3. Archimedes and Eureka!
There's a fun legend about the discovery of the principle of density. In ancient Greece, Archimedes had been asked by the king to find out if his crown was solid gold or if the king had been cheated with a gold-silver mixture. But he had to do it without breaking or destroying the crown. Archimedes struggled with the problem, but finally solved it when he got in his bathtub at the end of a long day. When he got in the tub, some of the water sloshed over the side, because he had a greater density than the water. His body pushed that water level higher until some of it overflowed the tub due to density. This same idea is why boats or planks of wood float, but rocks do not.
Icebergs present a unique problem for ocean-going ships that travel into the Arctic and Antarctic circles. Because the density of water changes as the temperature drops, ice floats. Also, icebergs are made of frozen freshwater, whereas the cold water around them is salty sweater; salt water has a higher density than freshwater, so combined with the frozen properties of the freshwater, icebergs float. The problem for these ships is the position of the iceberg in the water. Some estimates say that less than ten percent of the iceberg isactually visible above the surface, and the remainder can extend out dangerously before the ship is closer to the tip. This is the origin of the warning, "That's just the tip of the iceberg."
Current Density Formula
Air Resistance Formula
Current, Resistance, Voltage, and Power
Macroscopic Physical Properties of Matter