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# Lesson_Text_1.1 - 1 Lesson 1.1 1 Units and Unit Conversion...

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1 Lesson 1.1 1. Units and Unit Conversion Physical quantities are identified by their magnitudes and units. The unit of a physical quantity identifies the type of quantity that is measured. In this course we will be using SI system of units. In this system: The unit of length is the meter (m) The unit of mass is the kilogram (kg) The unit of time is the second (s) The units of many other physical quantities are obtained by combining the units of length, mass and time. For this reason, the units of length, mass and time are called the fundamental units . Units obtained from fundamental units are called derived units . For example: The unit of area is the m 2 . The unit of volume is the m 3 When solving problems, all units must be converted to SI. If length is measured in centimeter (cm), it must be converted to m; if mass is measured in gram (g), it must be converted to kg. 1 m = 10 3 mm 1 m = 10 2 cm 1 m = 10 6 μ m 1 m = 10 9 nm 1 m 2 = 10 4 cm 2 1 m 3 = 10 6 cm 3 1 km = 10 3 m 1 Mm = 10 6 m 1 kg = 10 3 g 1 min = 60 s 1 hr = 3600 s 1 mm = 10 -3 m 1 cm = 10 -2 m 1 μ m = 10 -6 m 1 nm = 10 -9 m 1 cm 2 = 10 -4 m 2 1 cm 3 = 10 -6 m 3 1 g = 10 -3 kg Example 1 : Convert:

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2 km m 25 to hr s Solution : 3 1 25 10 25 6.94 6.94 . 3600 km m m m s hr s s - = = = Example 2 : Convert 2.2 cm 2 to m 2 . Solution : 2.2 cm 2 = 2.2 10 -4 m 2 = 2.2 x 10 -4 m 2 Example 3 : Convert 66 mm 3 to m 3 Solution: 66 mm 3 = 66 10 -9 m 3 = 6.6 x 10 -8 m 3 Example 4: The wavelength of red light is 625 nm. Write this in m. Solution : 625 nm = 625 10 -9 m = 6.25 x 10 -7 m Example 5 : Express: 3 3 g kg 3.5 in cm m Solution : 3 3 3 3 6 3 3.5 10 3.5 3.5 10 . 10 kg g cm kg m m - - - - = = × Example 6 : A wire has a diameter 0.5 cm and a length 12 cm. Compute the volume of this wire in m 3 .
3 Solution : A wire is a right circular cylinder and its volume is given by 2 V r l π = where r is its radius and l, its length. Here m x cm cm d r 2 10 25 . 0 25 . 0 2 5 . 0 2 - = = = = and l = 12 cm = 0.12 m. Therefore, ( 29 2 2 6 2 0.25 10 0.12 2.4 10 V m - - = × = × Example 7 : The radius of the earth is 6700 km. Find the volume of the earth and express it in m 3 . Solution : Earth is spherical and the volume of a sphere is given by: 3 4 3 V r = Here r = 6700 km = 6700 10 3 m = 6.7 x 10 6 m. Therefore, the volume of the earth is: ( 29 3 6 21 3 4 6.7 10 1.26 10 3 V m = × = × 2. Significant figures. Measured physical quantities are always approximate and cannot be expressed in exact numbers. Measurement always involves a level of uncertainty and we use significant figures to deal with this uncertainty. Significant figures

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## This note was uploaded on 05/01/2011 for the course PHY 2048 taught by Professor George during the Fall '10 term at Edison State College.

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Lesson_Text_1.1 - 1 Lesson 1.1 1 Units and Unit Conversion...

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