Motion and Rest
Motion and Rest are relative terms, no one can exist in a state of absolute rest or absolute motion. A body may seem to be at rest with respect to one object but may appear to be in motion with respect to another object. If you consider a passenger in a moving train, he is at rest with respect to his co – passengers, but in motion with respect to an observer standing on the ground.
Motion: A body is said to be in motion if it changes its position with respect to its surroundings.
For example: A car running on a road is in motion with respect to trees on roadside. The passengers sitting in a moving bus are said to be in motion with respect to an observer standing outside the bus, similarly, the blades of a rotating fan, the hands of a working wall clock, a spinning top and satellites are all in motion with respect to a fixed axis.
Rest: A body is said to be at rest if it does not change its position with respect to its surroundings.
For example: A table lying in a room is at rest with respect to the walls of the room, the chairs of the dining table are at rest with respect to the dining table, the passengers sitting in a moving bus are said to be at rest with respect to the driver of the same bus because their positions do not change with respect to the driver.
Types of Motion: There are different types of motion. They are rectilinear motion, circular motion and periodic motion.
Rectilinear Motion: Rectilinear motion is the motion of a body along a straight line.
For example: A train moving on a straight track and a stone falling from a height are in rectilinear motion.
Circular Motion: Circular motion is the motion of a body that moves along a circular path.
For example: Bodies in circular motion are the rotating blades of a fan, a child sitting on a merry – go – round and the tips of the hands of a clock.
Periodic Motion: Periodic motion is the motion that repeats itself at regular intervals of time. Every object executing uniform circular motion can be said to be executing periodic motion. The motion of the pendulum in a pendulum clock, the motion of a swinging cradle and the motion of the needle in a sewing machine are some examples of periodic motion.