Explain why non-standard units fail and why the SI system (metres) is necessary.
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Hook on why body measurements differ.
Padma measured a classroom table and found it was 13 handspans long. Hardeep got 14, and Deepa got between 13 and 14! Did the table change size? No! Their hands are simply different sizes. This is exactly why body parts are not reliable standard units for measurement.
Historical non-standard units used in India.
In ancient times, people used their own bodies to measure the world around them! They used the balisht (handspan), the length of their arm, or even their feet. Farmers often walked and counted their strides to divide their fields.
Visual showing different sized hands measuring the same object.
Because body parts vary from person to person, they cannot be used as reliable standard units.
Introduction to the International System of Units.
When people began travelling across the world, differing measurement units created immense confusion. To solve this, scientists globally adopted a standard set of measurements called the International System of Units or SI units.
Practice metric conversions.
For measuring larger distances, we know that 1 kilometre is equal to metres. The standard SI unit of length is divided such that 1 metre equals centimetres. On a typical 15-cm ruler, the smallest divisions show that 1 centimetre is exactly equal to millimetres. Therefore, if the distance between your home and school is 1.5 kilometres, you will have to travel metres to reach there. In the International System of Units, this base standard unit of length is called the .
Flashcards for key terms in this section.