When a body remains in one position for a long time, it is said to be at rest. For example, the chairs of the dining table are at rest unless and until they are moved, and the flower vase, table, and the blackboard in the class room are all at the position of rest.
The act, process or state of the change in place or positionof a body with respect to time and relative to the observer is said to be motion. For example the blades of a rotating fan, the hands of a working wall clock, a moving car, a spinning top and satellites are all in motion.
Rest and motion are relative terms
A body seems to be at rest with respect to one object, but may appear to be in motion with respect to some other object. For example, a person on a railway platform is at rest with respect to another person on the same platform, but is in motion with reference to a person looking at him from a train crossing that platform. Similarly, a passenger sitting in the train will appear at rest to another passenger on the same train.
Types of Motion
The various types of motion are
Rectilinear motion is the motion of an object that moves in a straight line. For example, a train moving on a track, a parade, coins tossed in the air are all in rectilinear motion.
Circular motion is the motion of an object that moves at a fixed distance from a fixed point. Here, all objects rotate in circular motion. So, circular motion is motion in which the body traverses a circular path. The hands of a clock, a merry-go-round, the blades of a fan, the wheel of a moving vehicle, satellites, a spinning top, are all good examples of circular motion.
Periodic motion is motion that repeats itself at regular intervals of time. Every body executing circular motion can be said to be executing periodic motion. For example, the pendulum of a wall clock moves at regular intervals, the bells in a church, a bouncing ball, a vibrating string and a swinging cradle are all in periodic motion.
Sometimes an object can display combinations of different types of motion:
- A moving car which moves straight on the road displays rectilinear motion but at the same time the wheels of the car which are moving in circles display circular motion. So a moving car displays both rectilinear and circular motion.
- In a sewing machine, the needle is in periodic motion whereas the wheels of the sewing machine are in circular motion. So a sewing machine displays circular and periodic motions.
If a body does not change its position with respect to time, then it is said to be at rest. If a body changes its position with respect to time, then it is said to be in motion. There are different types of motion. Rest and motion are relative terms. If you consider a passenger in a moving train, he is at rest with respect to his co-passengers, but is in motion with respect to an observer on the ground.
There are many examples of bodies that are relatively at rest. Trees, buildings and mountains are some examples of bodies that are relatively at rest with respect to each other. Some examples of bodies in motion are flying birds, moving trains, and the rotating blades of a ceiling fan.
There are different types of motion. They are rectilinear motion, circular motion and periodic motion.
Rectilinear motion is the motion of a body in a straight line. Examples of bodies in rectilinear motion are sprinters in a race along a straight track, the march-past of soldiers in a parade, and a bullet fired from a gun.
When a body moves along a circular path, it is said to be in circular motion. Examples of bodies in circular motion are the rotating blades of a fan, children playing on a merry-go-round, and the hands of a clock.
When the motion of a body repeats itself after a certain time period, it is called periodic motion. The motion of a pendulum in a pendulum clock, and the motion of needle in a sewing machine are some examples of periodic motion.