Q. What is basic need of SI Units?

Ans: The Importance of Units

Units give numbers a particular meaning. Example: I am 5 feet 10 inches tall. Feet and inches are units. I could have told you that I am five - ten. But you would only understand the information if you could figure out that I am talking about my height and that height is usually reported in the archaic English system of feet and inches. Sometimes you can get away without mentioning the units used to measure whatever you are talking about, science class is not one of those times.

Units can be most helpful when you are converting from one system of measurement to another like English to metric. If I want to convert 300 miles into kilometers,

If you look at each multiplier, you will notice that each is the same as an equation such as 1 mile = 5,280 feet, so each multiplier is the same as multiplying by 1. If you go down the equation and cancel units that appear in the numerator (top) and in the denominator (bottom) you start with 300 miles multiply by 1 five times and end up with kilometers. To find out how many kilometers there are in 300 miles, you have to do what each multiplier tells you to do. First, multiply 300 by 5,280, then multiply by 12, then multiply by 2.54, then divide by 100 and last divide by 1,000 to get 480 km.

Units can also help you catch errors when you write down and substitute numbers into equations. Be very suspicious that you may have forgotten something or inadvertently inverted something if you calculate the length of something and it comes out in sec/meter!