MOTION ( CLASS 9TH PHYSICS CBSE NCERT) Core Idea Motion is defined as change in position of an object with time . To describe motion, we must compare the position of an object with respect to a reference point . Without a reference point, we cannot decide whether an object is at rest or in motion . Motion is relative , meaning it depends on the observer. Spotlight Reference Point (Origin) A fixed point used to describe position of an object. Also called origin . Example: A school is 2 km north of a railway station → Railway station = reference point Motion is Relative Example: Passenger inside a moving bus: Relative to bus → at rest Relative to road → in motion Same object → different observations Motion Along Straight Line Simplest type of motion where an object moves along a st...
