Nearly Alone in the World
Below is a map of the world. Countries that use the metric system are indicated in green. Countries that have not yet adopted the metric system are shown in gray. A cursory examination of this map (you may need to click to enlarge the map) shows that only three countries in the entire world have not adopted the metric system: Burma, Liberia, and the United States of America!
The Metric System
The metric system of measurement is far easier than the English system that most Americans are accustomed to. This is mainly due to the fact that all units are in multiples of 10s, so it is easy to do calculations in your head. Also, working within the metric system, one never has to convert units. This is certainly not true of the English system, in which ounces may need to be converted to cups, miles to feet, acres to square feet, etc. For example, how many feet are there in half a mile? The linear measure, mile-equivalent in the metric system is the kilometer (kilo = 1,000, therefore a kilometer equals 1,000 meters). How many meters are there in half a kilometer? Correct, 500 meters. It’s that easy.
In science, there are really only a few major properties of measurement. These are:
• The dimensions or length of an object (or distance)
• The mass (or weight) of an object
• The space an object occupies (its volume)
• The temperature of an object
• Time
Nearly everything else can be derived from these five measurements. For example, the question “How fast is that object moving?”, really just involves a measure of the distance the object has traveled (first item on the list) divided by the time it has done so (fifth item on the list). You get speeds something like 3 meters per second, 60 kilometers per hour, etc.
Each of the five basic types of measurements listed above rely on specific scientific tools and are reported in a variety of units as shown in the Table below:
In the next several sections, we will briefly discus each of these five types of measurements, but first, lets discus a few suffixes and abbreviations commonly used with the metric system that will greatly simplify the process. The prefixes are derived from the Greek and refer to quantity. While additional prefixes and abbreviations exist to describe extremely small and large measures, the following will suffice for the vast majority of the measures we encounter inLabLearner.
As you will see, these quantitative prefixes and abbreviations never change and are used over and over again in the metric system. In the following sections we will even see that the exact same prefixes and abbreviations are used to describe different types of measures like volume, time, length, and mass.
Length
Key Concepts
•Length and distance are linear measures
•Even though a linear measure, distance doesn’t necessarily have to be in a straight line.
•Length is used to describe the dimensions or size of an object, as well as the distance between objects.
The meter is the basic unit of metric length and is always abbreviated as m. The meter stick is perhaps the most common piece of scientific equipment that most people come in contact with. The meter stick is typically made of a strip of wood that is exactly 1 m long. It is analogous to a yard stick in the English system, but slightly longer. Most meter sticks available in the United States have inches and feet marked on one side and metric marking on the other side. As essentially all of science uses the metric system, we will not discuss the English system further here.
A quick examination of a meter stick tells us much about the logic of the metric system. In the drawing below, we have shown the largest numerals you will see on a meter stick (i.e. 10, 20, 30, and so on). These represent the number of centimeters from the left end of the meter stick as we look at it. We can easily see that there are 100 cm in a meter (notice that the last major mark is 90 rather than 100, which would be at the extreme right end of the stick if it were labeled). At the exact center of the meter stick is the 50 cm mark. If you placed your finger under the meter stick and held it up at this point, you would find it to be perfectly balanced. That is because 50 cm is exactly one half of a meter.
Those who have worked with number lines when either learning or teaching math, will notice that a meter stick is very much like the positive side of a number line. Thus, if you placed your finger at the 40 cm mark and moved 30 cm to the right, you would arrive at 70 cm (40 + 30 = 70). If you start with your finger at the 60 cm mark and move it 40 cm to the left, you would arrive at 20 cm (60 – 40 = 20).
At this point we know that a meter consists of 100 centimeters, equally spaced along its length. To see centimeters better, lets examine the section of a meter stick enlarged between the left end of the stick and the 10 cm mark (below).
In this enlarged view, we see the second largest numbers on the meter stick, representing individual centimeter markings. Since this enlarged section of the meter stick only contains 10 cm, we know that it therefore represents only one tenth of a meter since a whole meter contains 100 cm.
Finally, in order to see the finest units represented on standard meter sticks (millimeters, mm, or 1/1000 m), we will once again need to enlarge our view, this time of the area between the left end of the meter stick and the 1 cm mark (below).
As can be seen, there are exactly 10 equal divisions of the 1 cm section of the meter stick represented here. These are the millimeters (mm). Millimeters are never actually numbered on meter sticks as they are too small. However, for ease of use, the fifth mm in each cm is typically represented as a slightly longer line. Since we can see that there are 10 mm in 1 cm and we know that there 100 cm in 1 m, we know that there are 1000 mm in a meter (10 X 100 = 1,000).
Now that we have discussed the meter, centimeter, and millimeter, all that is left is to discuss the next metric unit of length that is grater than a meter. As briefly mentioned above, a kilometer(km) is equal to 1,000 meters. Thus, if you were to drive in a car at 60 kilometers per hour (60 km/hr), you would travel 60,000 meters in one hour. For very large distances, scientists still use kilometers (often in combination with scientific notation). For example, the distance from New York City to Sydney, Australia is 15,989 km, the distance from the Earth to the Moon is 385,000 km, while the planet Saturn is 1.4 billion km away from the Earth. Thus, we can use the simple units mm, cm, m, and km to measure things as small as the thickness of our fingernail, to the distance of far away planets!
We say that length and distance are linear measurements in the sense that measured distances can be added together, as we demonstrated through the “finger-walk” along the meter stick above. For example, if you walk 10 m straight out from where you are standing, and then 6 m straight back, you will have walked a total of 16 m, even though you may end up standing only 4 m from the original point.
Length and distance do not rely on straight lines. Thus, we can measure the length around the middle of a basketball with a tape measure to determine its circumference. Even a winding trail in the woods has a specific, measurable distance.
Finally, length can be used to measure the dimensions of an object. For example, a large cardboard box may be 2 m long, 1.5 m wide, and 1.5 m high, while a book may be 26 cm high, 18.5 cm wide, and 2 cm thick. We will later see how such measurements are important for determining volume and density.
Key Vocabulary for Metric Length:
Centimeter: A metric unit of measurement equaling 1/100th of a meter. Abbreviated cm, there are 100 cm in 1 meter.
Dimension: The length, height, width, circumference, etc. of an object.
Distance: The amount of space between two objects or the extent an object moves from one place to another.
English system: A system of measurement used widely in the United States, but not generally used in science, involving units such as inches, feet, miles, gallons, ounces, cups, etc.
Kilometer: A metric unit of measurement equaling 1,000 meters. Abbreviated km.
Length: A distance between two points.
Meter: Basic unit of length in the metric system.
Meter stick: A scientific instrument used to measure length and distance in the metric system.
Metric system: A system of measurement used in science and in most countries of the world.
Millimeter: A metric unit of measurement equaling 1/1000th of a meter. Abbreviated mm, there are 1,000 mm in 1 meter.
Mass and Weight
Key Concepts
•Mass and weight are different, but related.
•The basic unit of mass is the gram, abbreviated g.
•The prefixes milli- and kilo- are used in conjunction with the gram to cover an immense range of masses.
The major potentially difficult concept involving weight is in understanding the simple distinction between mass and weight. Mass is the amount of matter present in an object. Scientists express mass in grams (abbreviated g). Using an instrument such as a triple beam balance(below), one can determine the mass of an object. For example, an apple or a large orange will likely have a mass of about 100 g.
Scientists place the sample (an apple for example) on the pan of the balance and then adjust the counterweights (poises) until the balance is “balanced”. The mass is then determined by the exact amount of counterweights that are required to bring the instrument into balance. A larger, stand-up version of a similar instrument is used in many doctor’s offices to determine the mass of patients.
While mass is a measure of the amount of matter in an object, weight is a measure of the Earth’s gravitation pull on an object. To determine the weight of an object, one can use a spring scale (right). In this case, the 
sample that’s weight is to be determined (an apple again, for example) is hung from the lower hook of the spring scale. This pulls on and extends the spring and the force of gravity exerted on the object is read directly from the markings on the scale. Similar types of scales are used by fishermen to weigh fish on board.
On Earth, the mass (in grams) as determined by a triple beam balance and the weight (also in grams) as determined by a spring scale are identical. Therefore, for measures on Earth, the terms mass and weight are often used interchangeably. However, if the apple, triple beam balance, and spring scale were taken to the Moon and the mass and the weight of the apple was again determine by both instruments, we would obtain a different result than on Earth. We would find that the mass would be the same on the Moon as it was on Earth, as determined by the triple beam balance. However, the weight of the apple would be be six times less on the Moon, as measured by the spring scale, than on Earth. This is because of the Moon’s much small size, which has a gravitational pull on objects on its surface that is approximately six times less than the Earth has. We would not detect a difference in mass using the triple beam balance because the reduced pull of gravity would affect the pull on the sample (apple) to the same degree as the balance’s counterweights. Thus, we would correctly find that the mass of the apple is identical on Earth and the Moon. This makes sense since we have defined the mass of an object to be the amount of matter it is composed of. The amount of matter in the apple would not change simply because it was transported from the Earth to the Moon.
While the mass and weight of an object are the same on Earth, in science it is usually best to refer to an object’s mass rather than weight, particularly since many calculations and equations use the term mass, indicating that a given relationship is the same regardless of where in the universe an experiment is performed.
In the previous section we learned that the basic unit of distance in the metric system is the meter. The basic unit of mass is the gram, abbreviated g. The prefixes milli- and kilo- are very commonly attached to the term gram, with their same meanings as we described in the section on length. Thus, a milligram (1/1000th of a gram) and a kilogram (1000 grams) are used for very small and very large masses, respectively. The term centigram (1/100th of a gram) is rarely used. A milligram (1 mg) is a very small amount of mass (for example, a speck of sawdust has a mass of about a mg, a single gain of sand may have a mass of several mg). One kilogram is the mass of one liter of water. Thus, the popular sized soft drink container, a 2 liter bottle, has a mass of about 2 kg when full. The mass of the Earth, on the other hand, is 1024 kg (1,000,000,000,000,000,000,000,000 kg). Thus, simply by using the prefixes milli- and kilo- in conjunction with the gram unit of mass, allows us to report a range of masses from that of a grain of sand to that of our entire planet!
Key Vocabulary for Mass and Weight:
Gram: The basic unit of metric mass and weight, abbreviated g.
Kilogram: 1000 grams, abbreviated kg.
Mass: The amount of matter an object contains.
Milligram: 1/1000th of a gram, abbreviated mg.
Spring scale: A scientific instrument that measures the force that gravity exerts on an object.
Triple beam balance: A scientific instrument that measures the mass of an object.
Weight: The gravitational pull on an object with a given mass. On Earth, the terms mass and weight are often used interchangeably.