The Metric System Basic Training

Introduction The metric system is a group of units used to make any kind of measurement, such as length, temperature, time, or weight. No other system of measurement ever used equals the metric system in simplicity. Scientists everywhere make measurements in metric units, and so do all other people in most countries.

Introduction A group of French scientists created the metric system in the 1790's. Since then, the system has been revised several times. The official name of the present version is Systeme International d'Unites (International System of Units), usually known simply as SI. The term metric comes from the base unit of length in the system, the meter, for which the international spelling is metre.

The Creation of the Metric System In 1790, the National Assembly of France asked the French Academy of Sciences to create a standard system of weights and measures. A commission appointed by the academy proposed a system that was both simple and scientific. This system became known as the metric system, and France officially adopted it in 1795. But the government did not require the French people to use the new units of measurement until 1840.

The Creation of the Metric System In the original metric system, the unit of length equaled a fraction of the earth's circumference. This fraction was 1/10,000,000 of the distance from the North Pole to the equator along a line of longitude near Dunkerque, France; and Barcelona, Spain. The French scientists named this unit of length the metre, from the Greek word metron, meaning “a measure”.

The Creation of the Metric System It is interesting to note that a portion of the earth’s surface was actually measured and the entire distance calculated—assuming the earth was a perfect sphere. Later, an iridium allow bar was cast with two lines etched along the ends. The distance between these lines was the standard meter.

The Creation of the Metric System The units for capacity and mass came from the meter. The commission chose the cubic decimeter as the unit of fluid capacity and named it the liter. A liter is a cube that is one decimeter on each side. The scientists defined the unit for mass, the gram, as the mass of a cubic centimeter of water at the temperature where it weighs the most. That temperature is about 4 °C (39 °F).

Using the Metric System The scientists who created the metric system designed it to fit their needs. They made the system logical and exact. Furthermore, it is necessary to know only a few metric units to make everyday measurements.

Using the Metric System The metric system is simple to use for two reasons. First, it follows the decimal number system--that is, metric units increase or decrease in size by 10's. For example, a meter has 10 parts called decimeters. A decimeter has 10 parts called centimeters. Units in the inch-pound system have no single number relationship between them. For example, feet and yards are related by 3's, but feet and inches are related by 12's.

Using the Metric System The metric system is a decimal system just as are the U.S. and Canadian money systems. In a decimal system, a unit is 10 times larger than the next smaller unit. For example, a meter equals 10 decimeters just as a dollar equals 10 dimes.

Using the Metric System Also, the metric system has only 7 base units that make up all its measurements. The inch-pound system has more than 20 base units for just its common measurements. Inch-pound units used for special purposes add many, many more base units to that system.

Metric Units of Measure Seven base (basic) units form the foundation of the metric system. Nearly all everyday measurements involve only four of these units. The meter is the base unit for length or distance. (2) The kilogram is the base unit for mass, the weight of an object when measured on the earth. (3) The second is the base unit for time. (4) The kelvin is the base unit for temperature. Most people, when measuring in metric units, use Celsius temperatures instead of kelvin temperatures. One kelvin is equivalent to one degree Celsius, but the two temperature scales begin at different points.

Metric Prefixes Most metric units have a prefix that tells the relationship of that unit to the base unit. These prefixes are the same no matter which base unit is used. This uniform system also simplifies metric measurement.

Metric Prefixes Greek prefixes are used to show multiples of a base unit. They make a base unit larger. For example, hecto means 100 times and kilo means 1,000 times. Latin prefixes are used to show the submultiples of the base unit. They make a base unit smaller. For example, centi means 1/100 and milli means 1/1,000.

Length and Distance The meter is used for such measurements as the length of a rope or of a piano or other large object. It also is used to measure the height of a mountain or the altitude of an airplane. A meter is slightly longer than a yard. Short lengths are measured in centimeters, or they may be measured in millimeters. Books, pencils, and other small objects may be measured in centimeters. Photographic film, small hardware, and tiny mechanical parts are measured in millimeters.

Length and Distance Long distances, such as those between cities, are measured in kilometers. A kilometer equals about 5/8 of a mile. A short distance, such as that between two buildings on the same block, is measured in meters.

Measuring Area Surface measurements tell how much area something covers. For example, the amount of carpeting needed to cover a floor is measured in square units. Most areas are measured in square meters. A square meter equals the surface covered by a square one meter long on each side. It is slightly larger than a square yard. Smaller areas may be measured in square centimeters or square millimeters. Large land areas, such as cities and countries, are measured in square kilometers.

Volume and Capacity Volume and capacity measurements tell how much space something occupies or encloses. A volume measurement tells the size of a box, and a capacity measurement tells how much the box can hold. Volume and capacity are both measured in cubic units, such as cubic meters or cubic decimeters. The volume of a box with each side 1 meter long equals 1 cubic meter. A cubic meter contains 1,000 cubic decimeters.

Volume and Capacity Most capacity measurements for liquids are made in units called liters. A liter equals a cubic decimeter and is slightly larger than a liquid quart. Smaller units include the deciliter (1/10th of a liter) and the milliliter (1/1000th of a liter). A milliliter equals a cubic centimeter.

Weight and Mass The mass of an object is not really the same as its weight because its weight changes with altitude. However, the two measurements are equal at sea level on the earth. The kilogram is a unit of mass. But most people who use the metric system think of the kilogram as a unit of weight.

Weight and Mass A kilogram is equal in mass to a liter of water. The amount is used to measure larger weights. The gram is used for small weight measurements. A gram equals 1/1,000 of a kilogram. For extremely small amounts, the milligram is used. The dose of an aspirin tablet and other medicines are measured in milligrams.

Time The metric system measures time just as the inch-pound system does for measurements longer than a second, For such measurements, the metric system does not follow the decimal system. For example, 60 – not 100 – seconds equal a minute, and 60 minutes equal an hour. Time measurements in both systems use a decimal arrangement for units longer than a year. Ten years equal a decade, 10 decades are a century, and 10 centuries are a millennium.

Time The metric system follows a decimal arrangement for time measurements shorter than a second. Scientists and others who work with electronic equipment, including computers and radar, use such measurements. For example, some electronic computers perform mathematical operations in microseconds and nanoseconds. A microsecond is 1/1,000,000 of a second, and a nanosecond is 1/1,000,000,000 of a second.

Temperature Most people who use the metric system have thermometers that are marked in degrees Celsius (°C). Water freezes at 0 °C and boils at 100 °C. The normal body temperature of human beings is 37 °C. Celsius has been the official name of the metric scale for temperature since 1948. But many people still call this scale by its old name of centigrade scale. The word centigrade means “divided into 100 parts.” The Celsius scale has 100 degrees between the freezing and boiling temperatures of water.

Temperature Scientists do not know of any limit on how high a temperature may be. The temperature at the center of the sun is about 15,000,000 °C. However, nothing can have a temperature lower than –273°C. This temperature is called absolute zero. It forms the basis of the Kelvin scale used by some scientists. One degree Celsius equals one Kelvin. Because the Kelvin scale begins at absolute zero, 0 K equals –273°C, and 273 K equals 0 °C.

Comprehension Questions Which nation first proposed the metric system. (slide 3) Which years in history was the metric system designed? (slide 3) What is the formal name for the metric system? (slide 3) How is the meter related to the earth” (slide 5)

Comprehension Questions 5. How heavy is a gram? (slide 7) How many base units make up the metric system? (slide 11) Name four of these base units? (slide 12) How does the metric system show larger multiples and smaller fractions of the base? (slide 13, 14) What units are used to measure small lengths? (slide 14)

Comprehension Questions 10. How is volume different from capacity? (slide 18) 11. How does the metric system define a liter? (slide 7, 19) 12. What is the relationship between a milliliter and a liter? (slide 19) 13. What is the relationship between a milliliter and a cubic centimeter? (slide 19)

Comprehension Questions What is the relationship between a kilogram and a gram? (slide 20) 15. What two scales are used to measure temperature in the metric system? (slide 24, 25) 16 What is the lowest possible temperature? (slide 25)