Sunday, 1 May 2011

Report Text_Measurements

Measurements

Measure Up!

Measurements help us describe the world and everything in it. Measurements can describe length, volume, weight, time, temperature, and countless other properties. People use measurements whenever they make something, whether it’s a batch of cookies or a 50-story skyscraper.
Weighing animals can be tricky. The panda keepers in China use a big scale that fits the panda and keeper. They subtract the weight of the keeper from the total to find the pandas weight!
Weighing animals can be tricky. The panda keepers in China use a big scale that fits the panda and keeper. They subtract the weight of the keeper from the total to find the pandas weight!
©K.Feng/GLOBIO.org
Without measurement, the world would be a mess. Bridges would end in the middle of rivers if engineers didn’t take measurements before building. You would be late for school constantly without a clock to measure time. 
Your clothes wouldn’t fit if they didn’t match the measurements of your body.  
Without a speedometer, a driver couldn’t stay at a safe speed. Without their built-inthermometers, refrigerators couldn’t keep food cold enough to stop the growth of harmful bacteria. If doses of prescriptionmedicine weren’t carefully measured, a sick person could take too much and become even sicker.
Counting things by hand is an easy way to count and you always have the tools! For things like medicine, counting twice is always a good idea.
Counting things by hand is an easy way to count and you always have the tools! For things like medicine, counting twice is always a good idea.
©Patti Adair

The Need for Standards

You can measure speed in kilometers per hour, miles per hour, or even meters per second. A speedometer is used in cars and other vehicles to measure speed. What are some other things you might measure the speed of?
You can measure speed in kilometers per hour, miles per hour, or even meters per second. A speedometer is used in cars and other vehicles to measure speed. What are some other things you might measure the speed of?
©G.Ellis/GLOBIO.org
People have always needed measurement, but long ago there were no standards or systems. Instead, they used the length or width of their fingers, arms, and feet as units of measurement. The problem, of course, was that everyone’s fingers, arms, and feet were not the same size. So over time, most governments developed standard systems of measurement. That means weights and measures that everyone in a particular place could agree upon.
Today, there are two main systems of standardized measurement in the world: the metric system and the English system.

The Metric System

The metric system is used by most nations for scientific work and in daily life. The scientists who developed the metric system in the late 1700s based it on scientific principles. They established the meter as the base unit of length. They declared the length of a meter to be 1/10,000,000 of the distance from the North Pole to the Equator. (Today scientists define a meter as the distance light in a vacuum travels in 1/299,792,458 of a second.)
Units in the metric system are based on factors of 10. Prefixes added to the base unit tell how many times larger or smaller the unit is. For example, “kilo” means 1,000. So a kilometer is 1,000 times larger than a meter. The chart shows the meanings of some prefixes used in the metric system.
Prefix (larger than base unit)
Meaning
Prefix (smaller than base unit)
Meaning
kilo-
1,000
deci-
10
hecto-
100
centi-
100
deca-
10
milli-
1,000

The English System

In the United States, scientists use the metric system. But another system is most often used for everyday measurements. It’s called the English system. Units in the English system aren’t based on scientific principles like those in the metric system. They’re based on units that developed long ago in England. For example, the unit of measurement called a yard may date thousands of years back to the time of King Henry I of England. A measurement was taken from his nose to the tip of his fingers.
Other commonly used units of measurement in the English system include the foot, yard, mile, ounce, pint, quart, gallon, and the Fahrenheit degree.
Property
Metric Units
English Units
 
Length
millimeter
centimeter
meter
kilometer
inch
foot
yard
mile
Volume
cubic centimeters
cubic meters 
cubic kilometers
cubic inches
cubic feet
cubic yards
Fluid Volume
milliliter
liter

fluid ounce
pint
quart
gallon
Mass
milligram
gram
kilogram
metric ton
ounce
pound
ton
Temperature
degree
Celsius (˚C)
degree Fahrenheit (˚F)
Time
second
minute
hour
day
year
second
minute
hour
day
year

Measuring Length

Tape measures are portable and were invented to make measuring length easier. Measuring tapes are used by builders, scientists, tailors, students, and just about everybody else.
Tape measures are portable and were invented to make measuring length easier. Measuring tapes are used by builders, scientists, tailors, students, and just about everybody else.
©Cumhur Kahveci
People can measure many different properties of an object using various measuring tools. Properties such as length, height, width, and distance are measured with rulers, meter sticks, and tape measures. Choose your tool based on what you are measuring. If you’re measuring something small, like your little finger, a ruler is a good choice. If you’re measuring something fairly large, like the length of a room, a tape measure would be the best tool to use.

Measuring Volume

The amount that a container will hold is its volume. You can use rulers, meter sticks, and tape measures to measure the volume of a rectangular object such as a shoebox. Measure the object’s length, depth, and width and then multiply the three numbers to find its volume. The formula is written as: length (l) X depth (d) X width (w) = volume (v).
To measure the volume of a liquid, pour the liquid into a graduated cylinder that is marked with units such as milliliters or fluid ounces.

Measuring Mass

Biologists often use small, portable measuring tools to help them collect important data. This scientist is weighing a wild lynx. The lynx was first put to sleep with a drug so it wouldn’t be scared or injured.
Biologists often use small, portable measuring tools to help them collect important data. This scientist is weighing a wild lynx. The lynx was first put to sleep with a drug so it wouldn’t be scared or injured.
©G.Ellis/GLOBIO.org
When you hop on a scale, you see a number of kilograms or pounds. But what you’re really measuring is the force of gravity pulling on you. Since the amount of gravity can differ from place to place, when scientists weigh something they prefer to measure its mass. Mass is the amount of matter in something. It stays the same regardless of gravity.
Scales and balances are used to measuremass. Many modern scales and balances aredigital and are very simple to use. Just place an object on the scale or balance and read the display.

Measuring Temperature

Some foods need to be heated to an exact temperature and prepared with specific cooking equipment. This process and measuring makes the food safe and tasty!
Some foods need to be heated to an exact temperature and prepared with specific cooking equipment. This process and measuring makes the food safe and tasty!
©K.Campbell/GLOBIO.org
Temperature is a measurement of heat. Thermometers measure the temperature of a solid, liquid, or gas. Traditional thermometers are tubes marked in degrees that contain a liquid such as mercury or alcohol. When the temperature rises, the liquid expands and rises up the tube. Other types of thermometers measure the amount of infrared radiation (or heat) an object gives off.

Measuring Time

Time is something most of us measure every day. We use many different clocks to tell time. Big Ben is in London England and is one of the world’s most famous clocks.
Time is something most of us measure every day. We use many different clocks to tell time. Big Ben is in London England and is one of the world’s most famous clocks.
©Lieke Voermans
The measurement of time is based on Earth’s movement. A year is the time it takes Earth toorbit the Sun. A day is how long it takes Earth to rotate once on its axis. Other units of time include the hour, minute, and second. People use clocks and watches to measure time.

Accuracy and Estimates

For measurements to be useful, they must be reasonably accurate. Sometimes it’s fine to estimate if a measuring tool is not available. For example, based on what you know about what temperatures feel like, you might estimate that the temperature is between 20 ° C to25 ° C. Even though your estimate is not exact, it is useful because it will let people know that it’s a warm day.

Measurement Mistakes and How to Avoid Them

Most of the time, it is important to use measuring tools to get exact measurements. Even when you use measurement tools, however, errors are possible. You may make small errors in using the tool or reading the measurement. These kinds of errors are random errors. To reduce random errors, take measurements several times. Then divide the sum of all the measurements by the number of measurements you made to obtain a mean value.
Errors also occur if the measuring tool or instrument is not working correctly. These are systematic errors. One way to avoid systematic errors is to use several different instruments of the same type to take measurements. Then find the mean value of the measurements taken with the different instruments.
Calculators can be found just about everywhere. The first calculators were big and only could add and subtract. Today they are digital and fast, and easy to find – on cell phones, PDAs, wristwatches, even built into many computer programs.
The first calculators could only add and subtract but today, they are digital and fast. Calculators can be found just about everywhere, on cell phones, PDAs, watches, and in many computer programs.
©G.Ellis/GLOBIO.org

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