ch - 8 Motion
class - 9
Answers
=> Fundamental quantity and derived quantity :
A fundamental quantity is a quantity which does not cares for any other quantity (he is like boss!) . For instance you may take example of time , you would have probably heard that idiom "time waits for non" same way it's clear that time doesn't change with respect to any other quantity . Whereas the derived quantity cares for other quantity and it can be derived from the fundamental quantities . Again for instance you may take an example of velocity . We know that if velocity changes with respect to time it's known as retardation or acceleration .
=> Scalar and vector unit :
Well ! Quantities in physics are classified based on two quantities and we lovingly call them scalars and vectors . Physical quantities which has only magnitude is said to be scalar . Like it's an independent value which don't need the involvement of "direction" in specifying itself . Whereas a vector is somehow a stubborn quantity . It needs both magnitude and direction to specify itself . For instance of scalar you may take mass , distance , time , speed .
And for instance of vectors you may take an example of displacement , force , velocity etc .
=> Distance and Displacement .
The first and the most important
differences between two is distance is a scalar unit . And displacement is a vector unit . Let me explain how . Distance is defined as total path travelled by an ignoring the direction in which the path goes . And displacement is strictly the distance between initial and final position in a straight line . Which is also the shortest distance between initial and final position .
=> Average speed and average velocity .
Average Speed is defined as the average rate by which the particle covers a distance on a given path (scalar unit) . Whereas Average velocity is the displacement of a body in unit time or rate of displacement which is absolutely a vector unit .
=> Motion is relative .
This basically means that motion has no meaning without asking " according to whom ?" Imagine if I'm sitting in a train the passenger sitting in front of me will be at rest for me . But a person standing outsing the moving train will say "hey ! Hey ! The guy is moving" . Same way I will perceive the person standing outside the train moving , but for him , he is at rest . This also boils down to motion has no meaning without asking a question "according to whom ?"