Rest and Motion
Category : JEE Main & Advanced
If a body does not change its position as time passes with respect to frame of reference, it is said to be at rest.
And if a body changes its position as time passes with respect to frame of reference, it is said to be in motion.
Frame of Reference : It is a system to which a set of coordinates are attached and with reference to which observer describes any event.
A passenger standing on platform observes that a tree on a platform is at rest. But the same passenger passing away in a train through station, observes that tree is in motion. In both conditions observer is right. But observations are different because in first situation observer stands on a platform, which is reference frame at rest and in second situation observer moving in train, which is reference frame in motion.
So rest and motion are relative terms. It depends upon the frame of references.
Types of motion
| One dimensional | Two dimensional | Three dimensional |
| Motion of a body in a straight line is called one dimensional motion. | Motion of body in a plane is called two dimensional motion. | Motion of body in a space is called three dimensional motion. |
| When only one coordinate of the position of a body changes with time then it is said to be moving one dimensionally. | When two coordinates of the position of a body changes with time then it is said to be moving two dimensionally. | When all three coordinates of the position of a body changes with time then it is said to be moving three dimensionally. |
| Ex.. (i) Motion of car on a straight road. (ii) Motion of freely falling body. | Ex. (i) Motion of car on a circular turn. (ii) Motion of billiards ball. | Ex.. (i) Motion of flying kite. (ii) Motion of flying insect. |
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