Class 9 Physics Notes & Question Answers |Entrancei
About Class 9 Physics Notes Physics is a basic discipline in the category of Natural Sciences, which also includes other disciplines like Chemistry and Biology. The word Physics comes from the Greek word ‘FUSIS’ meaning nature. Physics is the study of nature and its laws. We expect that all these different events in nature take place according to some basic laws and revealing these laws of nature from the observed events in Physics. Physics is a quantitative science. Here class 9 Physics notes to describe any physical phenomenon, measurements of different physical quantities is essential. Measurement of any physical quantity involves comparison with certain basic, arbitrary chosen, internationally accepted reference standard called unit. Measurement and Units in class 9 Physics Measurement of any physical quantity involves comparison with certain basic, arbitrary chosen, internationally accepted reference standard called unit. To measure a physical quantity we need some standard unit of that quantity. The measurement of the quantity is mentioned in two parts, the first part gives how many times of the standard unit and the second part gives the name of the unit. Thus, suppose I say that length of this wire is 5 metres. The numeric part 5 says that it is 5 times of the unit of length and the second part ‘metre’ says that the unit chosen here is metre. Fundamental and Derived Physical Quantities use in class 9 Physics There are a large number of physical quantities which are measured and every quantity needs a definition of unit. But, not all the quantities are independent of each other. Therefore, the physical quantities which can exist independently are called fundamental quantities. For example length, mass etc. All other quantities may be expressed in terms of fundamental quantities are called derived physical quantities. For example force, density etc.