Motion is the change in the position of an object with respect to its surrounding. Everything in the universe is in motion: even an object that seems still is moving, because the Earth is moving around the Sun. Motion is described in terms of distance, speed, acceleration and time. This lesson covers the types of motion, distance and displacement, speed, velocity and acceleration, graphs of motion, the three equations of motion, free fall, uniform circular motion, and centripetal and centrifugal force.
1. Rest and Motion
- Objects which do not change their position are said to be at rest (e.g. a book lying on a table, the walls of a room).
- Objects which change their position are said to be in motion (e.g. cars and buses running on the road, birds and aeroplanes flying in air).
- Motion is a relative phenomenon: an object appearing to be in motion to one person can appear to be at rest to another. Trees on the road side appear to move backward for a person travelling in a car, but appear to be at rest for a person standing on the road side.