Scientific Measurement

A very important part of science is being able to make very accurate measurements. Since scientists all over the world must be able to communicate their discoveries with each other, it is important that all scientists use the same units of measurement. The system of measurement used by all scientists is The International System of Units, which is abbreviated as the SI system and commonly referred to as the Metric System. The metric system was developed in France about 200 years ago. The metric system is based on repeating units of ten.

The SI (metric) unit for length is the meter. A meter is one ten millionth of the distance from the north pole to the equator. Prefixes are added to the word "meter" to describe things that are much longer or shorter than a meter. Some of these are:

1. centi=1/100th-- A centimeter (cm) is 1/100th of a meter.

2. milli=1/1000th-- A millimeter (mm) is 1/1000th of a meter.

3. kilo=1,000 A kilometer (km) is 1,000 meters

Most people in America don't use the metric units to describe length. Instead, most Americans use the English system which describes length in terms of inches, feet, yards, and miles. The following gives you an idea of how these systems compare with each other.

1. One inch is equal to 2.54 centimeters.

2. One foot is equal to 30.48 centimeters.

3. One meter is equal to 39.37 inches.

4. One mile is equal to 1.609 kilometers.

5. A very common running event is the 5k race. A 5k race is really a 5km race. Five kilometers is equal to about 3.1 miles.

6. 100 meters is equal to about 110 yards.

The amount of space on the surface of something is called its area. The basic SI unit for area is the square meter (m2). Areas which are composed of squares or rectangles are computed by multiplying the length by the width. This is abbreviated by the formula:

A = L X W. The answer is always expressed in "square" units.

A common way that real estate people and appraisers describe the living area of a home is in square feet. A home which is 50 feet long and 30 feet wide would have 1,500 square feet of living area. Carpet and other flooring is sold by the square yard.

Volume is the amount of space something occupies. A cube is a three dimensional container having 90 degree angle walls. Our classroom, for example, is a cube. It has three dimensions (length, width and height) and the walls, ceiling and floor all meet at 90 degree angles. The basic SI unit for volume is the cubic meter (m3). Volume is calculated by multiplying length by width by height. This is abbreviated by the formula:

V = L X W X H. A swimming pool which is 20 meters long, 10 meters wide and 2 meters deep would hold a volume of 400 cm3 of water.

Since the cubic meter is quite large, smaller units such as cubic centimeters (ccm3) are often used to describe volume. However, for things which have a volume between that of a cubic centimeter and a cubic meter, the liter (L) is commonly used. A liter is the volume of a cube 10 cm on each size. Soft drinks are often sold by the liter or two liter bottle. A liter is almost the same as the English unit of volume known as the quart. A quart is 32 fluid ounces and a liter is 33.8 fluid ounces. For very small volumes, the milliliter (mL) is often used. A milliliter is 1/1000th of a liter.

If you want to know the volume of an irregularly shaped object, it is best to place it in a graduated cylinder containing water. The amount of water displaced by the object is equal to the volume of that object.

Mass is the measure of the amount of matter in an object. On the earth's surface, mass is equal to weight. The SI unit for mass or weight is the gram (g). A kilogram (kg) is 1,000 grams. One kilogram is equal to about 2.2 pounds. A milligram (mg) is 1/1000th of a gram.

Density is mass (weight) per unit of volume. If you have equal volumes of gold and styrofoam, the gold will weigh more even though their volumes are the same. The gold weighs more because gold has a greater density than styrofoam. Density is equal to mass divided by volume: D = M/V. The answer is expressed as mass per volume. A common metric expression of volume would be g/cm3, which means grams per cubic centimeter.

The SI unit for temperature is degrees Celsius (C). The scale for measuring temperature is the Celsius scale, a.k.a. the centigrade scale. On the Celsius scale, water freezes at zero degrees and boils at 100 degrees.

The English unit for measuring temperature is degrees Fahrenheit (F). On the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees.

To convert centigrade to Fahrenheit the following formula is used: F = 1.8 X C + 32

To convert Fahrenheit to centigrade the following formula is used:

C = .56 X (F - 32) ***remember to do what is inside of the parenthesis first.

There is another scale for measuring temperature which is often used in physics and chemistry. This is the Kelvin scale. The Kelvin scale is just like the Celsius scale except that you add 273 degrees to degrees Celsius. So on the Kelvin scale, water freezes at 273 degrees and water boils at 373 degrees. The Kelvin scale was designed so that zero degrees Kelvin is absolute zero. Absolute zero is the coldest possible temperature. Absolute zero occurs with the complete absence of heat. Specifically, it is 273.16 C, or 459.7 F.

The SI units for time are seconds, minutes and hours. There are 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day.

Graphing: A graph is a good way of looking at data to find possible relationships. A graph is a picture of data. Graphs usually have these features:

1. abscissa--the horizontal or X axis

2. ordinate--the vertical or Y axis

3. origin--the place where the horizontal and vertical axes meet.

Lab. assignment: In your group, conduct the following experiment and graph the results. With a rubber band attached to the end of a ruler, stretch the rubber band to varying distances. Release the rubber band and allow it to be propelled. Measure how far back the rubber band was stretched and how far it traveled. Graph the results. On the X axis, plot the length which the rubber band was stretched. Stretch it to at least five different lengths. On the Y axis, plot how far the rubber band traveled. This lab. activity is worth 50 points for each student. If another person is shot with the rubber band, a ten point penalty will be deducted from the grade of the shooter each time this occurs. When finished, turn in your graph. Be sure to include the names of all people who participated in the group.

Scientific Measurement Study Sheet