SI System Units of Measurement

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Information about SI System Units of Measurement

Published on August 18, 2008

Author: acurry26


THE SI system and units of measurement : THE SI system and units of measurement Units of Measurement Measurement : Measurement Measurement is used to measure quantities. Quantity is something that has magnitude, size, or amount (volume). A quantity is not the same as a measurement. SI system of measurement : SI system of measurement In the late 18th century, scientists used the metric system. The metric system is a forerunner to the SI System. Scientists all over the world use a single measurement system called Le Systeme International d’Units, abbreviated SI. It was adopted in 1960 and has both base units and derived units. SI Base units : SI Base units The most common base units that we will study include: Length : Length The SI standard unit for length is the meter. A distance of 1m is about the width of an average doorway. To express longer distances, the kilometer (km) is used. One kilometer is equal to 1000 m. To express shorter distances, the centimeter (cm) is used. One centimeter is equal to 1/100 of a meter. Length can be measured using a meter stick or rulers. Mass : Mass Mass is a measure of the quantity of matter. The standard unit for mass is the kilogram (kg). The gram (g), which is 1/1000 of a kg is used for measuring masses of small objects such as flasks and beakers. Mass is typically measured using a balance. Mass is different from weight. Weight is a measure of the gravitational pull on matter. The weight of an object increases as gravity acts on it. The weight of an object on the moon is about 1/6th of its weight on Earth. So, a human on Earth who weighed 126 lbs. would weight how much on the moon? Time : Time The standard unit of measurement for time is the second (s). Time can be measured using stop watches, clocks, count down timers, and other time pieces. Larger amounts of time are measured in minutes and hours. There are 60 seconds in one minute. There are 60 minutes in one hour. Given that there are 24 hours in one day, how many seconds are there in one day? Temperature : Temperature The standard unit of measurement for temperature is degrees Kelvin (K). Temperature can also be measured in degrees Celsius (°C) and degrees Fahrenheit (°F). To convert degrees Celsius (°C) to degrees Fahrenheit (°F) multiply by 1.8 and then add 32. To convert degrees Fahrenheit to degrees Celsius, subtract 32 and then divide by 1.8 ° K= °C + 273 Temperature is measured using a thermometer. (measures the degree of heat or coolness) Derived units : Derived units Derived units are combinations of base units. They are produced by multiplying or dividing standard units. The derived units we will study include: Area : Area Area is length times the width. It is expressed as square meters. Area can also be expressed as cubic centimeters. What is the area of a rectangle that has an a length of 6 cm and a width of 16 cm? 16 cm 1 6 cm 11111cmam Volume : Volume Volume is the amount of space occupied by an object. The derived SI unit for volume is cubic meters. The cubic meter is rather large, so a more common unit of cubic centimeters is more commonly used. Non-SI units are also used to measure volume such as the milliliter (mL) and the liter (L), which is 1000 cm3. There are 1000 mL in 1 L. Beakers, flasks, and graduated cylinders are often used to determine the volume of liquids. density : density Density is the ratio of mass to volume, or mass divided by volume. It can be written: density=mass/volume or D=m/V Density is a characteristic physical property of a substance that does not depend on the size of the sample. As the mass of an object increases, its volume increases. * Question: Are raisins, more or less dense than soda water? Let’s see!

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