# Motion Class 9 Physics Lesson – Motion

Motion of an object is change in its position with respect to its surrounding. An object is said to be in motion if it is changing its position from one place to another place with respect to surrounding in certain time. There are following important categories of motion,

i) Translational motion

ii) Rotational motion

iii) Vibrational motion

iv) Random motion.

The important parameters to discuss the motion are

a) Distance: The actual path travelled by body during its entire motion is known as the distance or path length.

SI unit of distance or path length is meter

b) Displacement: Displacement is the shortest and straight line distance between initial and final position of object.

SI unit of displacement is meter

### Some important points:

• Distance can never be zero, negative but displacement can be zero, negative or positive.
• If initial and final position of object is along same line, then the magnitude of distance and displacement is same.
• Distance is scalar while displacement is vector quantity.

Updated: August 4, 2021 — 8:10 pm