# Physical Quantities and System international units

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#### Students’ Learning Outcomes

·         Define a physical quantity with examples.
·         Apply the prefixes (mile, kilo, and cent) and interpret the units.
·         Inter convert smaller units and bigger units.
·         Interpret S.I. units in the daily life.
·         Investigate why it is desirable for scientists to use the S.I. units in their work.

# Concept Map

·         Measurement is a different phenomenon from counting, even though both associate with numbers.
·         A physical quantity is a quantity that can be measured or it is a physical property that can be qualified. Length, mass, time & volume etc. are the examples of physical quantities. They are measured in suitable units such as meter, kilogram, second, liter, and meter etc.
·         Value of physical quantity is expressed as the product of a numerical value and a unit of measurement.
·         S.I. is an abbreviation of System International or International System: our metric system of measurements. It is an internationally standardized system, giving a common language between nations and between the different branches of science and technology.
·         At the international conference on weights and measures in 1960, a coherent system of metric units known as international system of units was adopted. It is officially abbreviated as SI in all languages.
·         One meter is the distance traveled by light in vacuum during a time of 1/299,792,458 second.
·         A standard kilogram is the mass of platinum and iridium alloy cylinder kept at the “international Bureau of Weight and Measures” near Paris.
·         A second is the duration in which the cesium-133 atom completes 9,192,631,770 vibrations.
·         In calculations we must be careful that the entire unit are S.L units with same multiples or sub multiples of the basic units. The terms used internationally for the multiples and sub multiples for various units are called prefixes.
·         Standard measurement helps us in different fields of life. These values always give us accurate results which are accepted by everyone. Most countries today use the metric system. Buying and selling between countries is much easier if everyone uses the same system.

# Material / Resources

Charts of S.I. units and pictures of measuring instruments from different science books, newspaper etc., two buckets, stopwatches and graduated cylinders

#### Sum up / Conclusion

·         Complete the lesson by showing S.I. chart to the students. Ask them the following questions:
Q1. What is the basic unit of length?
(Expected response: Meter)
Q2. What is the basic unit of time?
(Expected response: Second)
Q3. Write one multiple and one sub multiple units of length.
(Expected response: Km, Cm,)

#### Assessment

·         Assess the students by asking the following questions:
Q1. How many seconds are there in an hour?
(Expected response: 3600 seconds)
Q2. What is the appropriate mass of your school bag?
(Expected response: 4-5 kg)