si units of measurements

SI Units Of Measurements•Measurement make sense only, if it has both number and Unit.•ex. 6 inches, 12 dollars.•Some examples of units are inches, feet, pounds, degree Fahrenheit.

•A set of measuring units called SI, or the Inter national System of Units.

•SI is a revised version of metric system, which was originally developed in France in 1791.

•The abbreviation stands for French name System International d’Unites.

Base Units and Derived Units

• SI has 7 metric units known as base units, • which are as follows.

Quantity Unit Symbol

Length meter m

Mass kilogram kg

Temperature Kelvin K

Time second s

Amount of substance

mole mol

Electric current

ampere A

Luminous Intensity

candela cd

Derived Units Additional SI Units, which are made from a combination of base units

ex. Area, Volume, Density etc.

Quantity Unit Symbol

Area Square meter m²

Volume Cubic meter m³

Density Kg per cubic meter Kg/m³

Frequency hertz Hz

wavelength meter m

VelocitySpeed

m/s directionm/s

v v7

Acceleration Meters per second per second

m/s² or m/s/s

Quantity Unit Symbol

Power J /s W

Force Kg.m/s² N

Momentum Kilogram meter per s Kg.m/s

Work Joule J

Energy Joule J

•

1) Length a . The distance from one point to another point. b. Base unit is the meter (m). c. Centimeter or inch ruler is used to measure length

c

2). Mass• a. The amount of matter in a substance.• b. Base unit - kilogram (kg).• The tool used is a triple beam balance. (Grams g)

3). Temperature• a. The amount of kinetic energy a substance has.• b. SI unit is the Kelvin (K).

Volume a. The amount of space a substance occupies.

For regular shaped solids use the equations L X W X H. but for an irregular shaped solid we use a graduated

cylinder and measure how much water is displaced. ( m³ or L ) b. Base unit is the liter (L). 1 L = 1 m³

Temperature• Definition – A measure of the heat of an object

• Thermometer – A device that measures temperature, • usually with mercury.

• There are three temperature scales .• 1) Fahrenheit scale. 2) Celsius scale 3) SI Unit scale or Kelvin scale.

• Some baseline temperatures in the three different temperature scales: Temperature Celsius Fahrenheit Kelvin

Symbol °C °F K

Melting point of ice 0 32 273

Boiling point of water

100 212 373

-273 -460 0

International system of units (SI)– Used in many countries to have a uniform scale of

measurement. – 1. Based on multiples of 10

Common metric prefixes

Conversions: Units based on 10

Conversions

C/100 = (F-32)/180

Celsius = 5/9 X (Fahrenheit -32)

Fahrenheit =( 9/5 x Celsius) + 32

Kelvin = Celsius + 273

• An “Astronomical Unit” (AU) is a convenient way to measure distances in the solar system.

• It is the average distance from the earth to the sun, about 150 million kilometers (1.5 X 108 km or 93 million miles)

• 1 mile = 1.6 km.

• One light year is equal to the distance that light travels through space in one year (9.46 × 1012 km)

Units of distance in space

Accuracy & Precision in Measurement

Precision

•Depends on the How finely tuned your measurements are or how close they can be to each other.

It depends on measuring tool.

•Determined by more number of significant digits.

•If the analog clock is showing 5 minutes and the digital clock is showing 5 minutes 15 seconds, the digital clock is showing more precise measurements.

Accuracy:

– How close you are to the actual value

– Depends on the person measuring

– Even if the digital clock is more precise by showing 5 minutes 15 seconds but if it is running slow. Although the clock is precise to the nearest seconds, the time displayed is not accurate.