Q. Describe SI System and Standards

Ans:

What units you will you use science class? Long ago people decided that the "foot" must be standardized so that when I measure a cow and tell you about it, you can use this information so that you know the exact size of the cow. Originally this standard was the King's foot, but that would change with each new "ruler." Someone then had the brilliant idea of a standard length for a foot. Then all measurements were made compared to this "standard foot" which was not subject to growth or death. This system of measurements had the drawback of making the math hard - 12 inches to a foot, 3 feet to a yard, 5,280 feet in a mile and so on.

Beyond the basic meters, kilograms and seconds, we define some secondary or derived standards like amperes, moles, and candela. They are defined in terms of meters, kilograms and seconds.

But we find that there are some combinations of units that pop up a lot so we give them names like newtons or joules which are equivalent to a particular product/quotient of the basic three units, meters, kilograms and seconds.