Since matter is anything that occupies space and has weight, it can be said that all kinds of matter have certain properties in common. These properties are inertia, mass, gravitation, weight, volume, and density. These properties are briefly covered in this section and are referred to as the general properties of matter.

Inertia of matter is perhaps the most funda-mental of all attributes of matter. It is the tendency of an object to stay at rest if it is in a position of rest, or to continue in motion if it is moving. Inertia is the property that requires energy to start an object moving and to stop that object once it is moving.

Mass is the quantity of matter contained in a substance. Quantity does not vary unless mat-ter is added to or subtracted from the substance. For example, a sponge can be compressed or allowed to expand back to its original shape and size, but the mass does not change. The mass remains the same on Earth as on the sun or moon, or at the bottom of a valley or the top of a mountain. Only if something is taken away or added to it is the mass changed. Later in the unit its meaning will have a slightly different connotation.

All bodies attract or pull upon other bodies. In other words, all matter has gravitation. One of Newtons laws states that the force of attrac-tion between two bodies is directly proportional to the product of their masses and inversely pro-portional to the square of the distance between their two centers. Therefore, a mass has less gravitational pull on it at the top of a mountain than it has at sea level because the center is displaced farther away from the gravitational pull of the center of Earth. However, the mass remains the same even though the gravitational pull is different. Gravity also varies with latitude. It is slightly less at the equator than at the poles due to the equators greater distance from the center of Earth.

The weight of an object is a measure of its gravitational attraction. The weight depends upon the mass or quantity that it contains and the amount of gravitational attraction Earth has for it. Weight is a force, and as such it should be ex-pressed in units of force.

Since gravity varies with latitude and height above sea level, so must weight vary with the same factors. Therefore, a body weighs more at the poles than at the equator and more at sea level than atop a mountain. In a comparison of mass and weight, mass remains constant no matter where it is, but weight varies with latitude and height above sea level.

Volume is the measure of the amount of space that matter occupies. The volume of rectangular objects is found directly by obtaining the product of their length, width, and depth. For determin-ing the volume of liquids and gases, special graduated containers are used.

Density 

The mass of a unit volume of a substance or mass per unit volume is called density. Usually we speak of substances being heavier or lighter than another when comparing equal volumes of the two substances.

Since density is a derived quantity, the density of an object can be computed by dividing its mass (or weight) by its volume. The formula for deter-mining the density of a substance is

where D stands for density, M for mass, and V for volume.

From this formula, it is obvious that with mass remaining unchanged, an increase in volume causes a decrease in density. A decrease in volume causes an increase in density.

The density of gases is derived from the same basic formula as the density of a solid. Pressure and temperature also affect the density of gases. This effect is discussed later in this unit under Gas Laws.

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