Physical+Quantities+and+Conversion+of+Units

Physical Quantities and Conversion of Units

Physical Quantities __**﻿**__There is a system of measurement that has been agreed internationally and it is called the System International of Units (SI). It defines 7 base quantities and units. The 7 base and quantities and units are shown in the picture below.

The definitions are based on specific physical measurements that can be reproduced in laboratories around the world. However, the only exception to that is the kilogram. All other quantities other than the base quantities are known as derived quantities. Both the quantity and its units are derived from a combination of base units, using a defining equation.

__Prefixes__
Prefixes are used for very large or very small numbers. We can use standard prefixes with the base units.The main prefixes that we need to know are in the picture below.

While converting units, prefixes are very helpful tools. Some examples are as follows:
 * When you want to convert 56000000J to a unit easier to write down, you can use the prefixes and change it to 56MJ
 * When you want to convert 35mg to g, you can use the prefixes to convert 35mg to 0.035g
 * When you want to convert 0.035g into kg, you can use the prefies and hence convert 0.035g into 0.000035kg.

Reflection
After learning about how to convert units and also learning about physical quantities, I find some of it very useful to me. By learning about the SI units, I am able to note what kinds of units I should use in the future when taking down notes during lab lessons. For the conversion of units, it is also very useful to me. Try to imagine that you need to write a zero 10 times. I'm betting that you will even miscount the number of zeros. With this tool of converting units, I can decrease the number digits but still get the same value. Thus, I feel that this lesson is very useful to me.