What makes up density

The gravitational force G of the earth pulls downward and is proportional to the mass of an object. The gravitational force on an object is also called weight. The force due to gravity is greater on objects that are more massive, or weigh more. The buoyant force B of water pushes up. In the third century B. He observed that the volume of water pushed out of a tub, or displaced, by an object was equal to the volume of the object.

The buoyant force of the water is equal to the weight of the water displaced. An object accelerates when the forces on that object are unequal. Although acceleration is commonly used to describe an object that is speeding up, the scientific definition of acceleration means changing speed. An accelerating object can be speeding up or slowing down. An object will always move in the direction of the greater force. An object may accelerate downwards sink or upwards rise in a body of water.

If all of the forces on an object are balanced, there is no acceleration. In this case, the object may not move—like a book sitting on a flat table—or the object may move at a constant speed—like a car traveling at a steady 80 kilometers per hour. In the water, an object might remain still either at the surface or within the water column.

Three cubes of the same size, but with different masses and thus different densities, are placed in three beakers of water Fig. Because the cubes are identical in volume, they displace the same amount of water.

Buoyant force is represented in Fig. These arrows are the same length for each of the cubes, indicating that the strength of the buoyant force acting on each cube is the same.

Because the masses of the cubes are not equal, the gravitational force G acting on each cube is different. Gravitational force is represented in Fig. These arrows are different lengths for each cube, indicating that the amount of the gravitational force is different for each cube. The downward pointing arrow in Fig. The downward pointing arrow is the longest in Fig 2.

The density of the cube relative to the density of water determines if the cube will float, sink, or be neutrally buoyant:. This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. This means the gas is less dense. Density also depends on the material.

A piece of iron with the same dimensions as a piece of aluminium will be heavier because the atoms are more closely packed and each iron atom has much more mass than each aluminium atom. Scientists can measure density by measuring the mass of a certain volume of the material, for example, one cubic centimetre.

Density can be calculated using the equation:. This is when:. What is the density of a material if 0. He realized that the amount of water that spilled was equal in volume to the space that his body occupied. This fact suddenly provided him with a method for differentiating a mixed silver and gold crown from a pure gold crown. Because a measure of silver occupies more space than an equivalent measure of gold, Archimedes placed the craftsman's crown and a pure gold crown of equivalent mass in two tubs of water.

He found that more water spilled over the sides of the tub when the craftsman's crown was submerged. It turned out that the craftsman had been defrauding the King! Legend has it that Archimedes was so excited about his discovery that he ran naked through the streets of Sicily shouting "Eureka! Archimedes had used the concept of density to expose the fraud. Density is a physical property of matter that expresses a relationship of mass to volume.

The more mass an object contains in a given space, the more dense it is. It is important to remember, though, that this relationship is not just about how closely packed together the atoms of an element or the molecules of a compound are. Density is also affected by the atomic mass of an element or compound. Since different substances have different densities, density measurements are a useful means for identifying substances.

For example, how could you distinguish a metric ton of feathers versus a metric ton of bricks, shown in Figure 1, if you could not see them? One metric ton of either feathers or bricks will have an identical mass of 1, kilograms one metric ton. However, a metric ton of feathers will occupy a volume of almost million cm 3 about the size of four tractor trailer trucks , while a metric ton of bricks will occupy only one-half million cm 3 about the size of a large-screen TV. The bricks are denser than the feathers because their mass is packed into a smaller volume.

This relationship between the mass and volume of a substance is what defines the physical property of density:.

Density is defined as the ratio of an object's mass to its volume , as shown in the equation above. Because it is a ratio, the density of a material remains the same without regard to how much of that material is present. Density is therefore called an intensive property of matter. Mass is the amount of matter contained in an object and is commonly measured in units of grams g. Let's look at an example. A typical brick has a mass of 2, g and occupies a volume of 1, cm 3.

Using the equation above, we can calculate the density of the brick:.