Weight differs as a response to the gravitational pull of the planet, moon, or other body on which it is measured. Given its invariable value, scientists typically speak in terms of mass rather than weight. Thus a person's weight varies according to gravity, and would be different if measured on the Moon mass, on the other hand, is the same throughout the universe. The acceleration component of weight is a result of Earth's gravitational pull, and is equal to 32 ft (9.8 m) per second squared. Weight is a measure of force, which Newton's second law of motion defined as the product of mass multiplied by acceleration. Though the two are relatively convertible on Earth (1 lb = 0.4536 kg 1 kg = 2.21 lb), they are actually quite different.
(kg) is a unit of mass in the metric and SI systems. However, the pound (lb) is a unit of weight in the English system, whereas a kilogram It is understandable why people confuse mass with weight, since most weight scales provide measurements in both pounds and kilograms. In this analogy, mass is equivalent to the apple, and weight the pie, while the acceleration due to gravity is the "something else" in weight. Of course, an apple is an ingredient in an apple pie, but the pie contains something else -actually, a number of other things, such as flour and sugar. Most people who are not scientifically trained tend to think that mass and weight are the same thing, but this is like saying that apples and apple pies are the same. Mass is a measure of inertia, meaning that the more mass something contains, the more difficult it is to put it into motion, or to stop it from moving. To refer again to the laws of motion, in his first law, Newton identified inertia: the tendency of objects in motion to remain in motion, or of objects at rest to remain at rest, in a constant velocity unless they are acted upon by some outside force. The more matter an object contains, the more mass. The form or state of matter itself is not important: on Earth it is primarily observed as a solid, liquid, or gas, but it can also be found (particularly in other parts of the universe) in a fourth state, plasma. Matter, in turn, can be defined as physical substance that occupies space is composed of atoms (or in the case of subatomic particles, is part of an atom) is convertible into energy -and has mass. This, of course, is a statement that belongs to the realm of physics for a chemist, it is more useful -and also accurate -to define mass as the quantity of matter that an object contains. In his second law of motion, Sir Isaac Newton (1642-1727) defined mass as the ratio of force to gravity. Though length is easy enough to comprehend, mass is more involved. In the SI system, density is typically expressed as grams per cubic centimeter (g/cm 3), equivalent to 62.42197 pounds per cubic foot in the English system. Density can also be viewed as the amount of matter within a given area. As its name implies, there are 1,000 milliliters in a liter.ĭensity is the ratio of mass to volume -or, to put its definition in terms of fundamental properties, of mass divided by cubed length.
Volume is usually expressed in cubic units of length -for example, the milliliter (mL), also known as the cubic centimeter (cc), is equal to 6.10237 Volume, then, is measured in terms of length, and can be defined as the amount of three-dimensional space an object occupies. Height, perpendicular both to length and width, makes the third spatial dimension -yet all of these are merely expressions of length differentiated according to direction. Length provides one dimension, while width provides a second perpendicular to the third. Width and height are not, for the purposes of science, distinct from length: they are simply versions of it, distinguished by their orientation in space. The volume of a cube, for instance, is a unit of length cubed -that is, length multiplied by "width," which is then multiplied by "height." Most qualities of the world studied by scientists can be measured in terms of one or more of four properties: length, mass, time, and electric charge. HOW IT WORKS Fundamental Properties in Relation to Volume and Density Measuring density, for instance, aids in determining the composition of a given substance, while volume is a necessary component to using the gas laws. All of these -mass, density, and volume -are simple concepts, yet in order to work in chemistry or any of the other hard sciences, it is essential to understand these types of measurement. Mass, in turn, plays a role in two properties important to the study of chemistry: density and volume. Among the physical properties studied by chemists and other scientists, mass is one of the most fundamental.