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**The SI System of Measurement**

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**Objectives Identify the base units for the SI System**

Understand how and when to use derived units. Identify the differences between mass and weight.

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**Le Système International d’Unités (SI)**

Meter Kilogram Kelvin Second Derived Unit

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The SI System Le Système International d’Unités (SI) is a modern version of the metric system based on a decimal system. In 1960, the SI System was a revision of the meter/kilogram/second version of the Metric System. The system has been nearly globally adopted. Three principal exceptions are Burma (Myanmar), Liberia, and the United States. The United Kingdom has officially adopted the International System of Units but not with the intention of replacing customary measures entirely.

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**The SI System Length Mass Weight Time Temperature**

The SI unit for length is the meter (m). Mass The amount of matter in an object is called mass. The SI unit of mass is the kilogram (kg). Weight Weight is a measure of the gravitational force on an object. The SI unit for force is the newton (N). Time Time is the interval between two events. The SI unit for time is the second (s). Temperature Temperature is a measure of the average kinetic energy of the particles that make up a material. The SI unit for temperature is the kelvin (K). Absolute zero is the coldest possible temperature.

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**The SI System Base Units**

Measurement Base Unit Length Meter Mass Kilogram Time Second Temperature Kelvin

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Kelvin Temperature Although Kelvin is the SI unit, in practice we will use the Celsius Scale

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**Derived Units Area Volume Density**

Area is the amount of surface included within a set of boundaries. The SI unit for area is square meters (m2). Volume Volume is the amount of space occupied by an object. The SI unit for volume is cubic meters (m3). Density Density is the measure of the amount of matter that occupies a given space. The SI units for density are expressed in grams per cubic centimeter (g/cm3), grams per milliliter (g/mL), and kilograms per cubic meter (kg/m3).

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Derived Units Other units in the SI are derived (made) by combining units: Quantity Measured Formula Units in Formula Base Unit Other Common Units Area A = l x w A = m x m m2 cm2 Volume Vol. = l x w x h Vol. = m x m x m m3 cm3, mL, L 1 cm3 = 1 mL Density D=m/v D = g/cm3 g/cm3 kg/m3, g/mL

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Larger/Smaller Units The SI system uses prefixes on the base units to make the unit larger or smaller: Prefix Meaning Use Kilo- 1000 times the base unit Kilometers would be used to measure distance between cities. Centi- The base unit divided by 100 Centimeters would be used to measure your textbook. Milli- The base unit divided by 1000 Milligrams are often used for indicating the amount of a certain substance in foods.

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**Practice What unit would you use to:**

measure the distance from your house to the school? determine your mass? measure the length of 5th Block? if you were preparing a weather report? measure the mass of a paper clip?

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**Practice (cont.) What unit would you use if you were:**

measuring the thickness of your pencil/pen? measuring the mass of a penny? writing a density? measuring the volume of this room? measuring the area of the football field?

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