Motion: Physics for RAS/RTS Mains examination

Motion is a change in position of an object with respect to time. Motion is typically described in terms of displacement, distance, velocity, acceleration, time and speed.

The branch of physics which deals with the study of motion of material objects is called mechanics.

Mechanics is divided into following branches.

(i) Statics : Statics is the branch of mechanics which deals with the study of motion of objects under the effect of forces in equilibrium.

(ii) Kinematics :

It is that branch of mechanics which deals with the study of motion of object without taking into account

the factors (i.e. nature of forces, nature of bodies etc.) which cause motion. Here time factor plays an

essential role.

(iii) Dynamics :

It is that branch of mechanics which deals with the study of motion of objects taking into account the factors which

cause motion.

Rest : An object is said to be at rest if it does not change its position with time, with respect to its surroudings.

A book lying on a table, a person sitting in a chair are the examples of rest.

Motion : An object is said to be in motion if it changes its position with time, with respect to its surroundings.

Example : A bird flying in air, a train moving on rails, a ship sailing on water, a man walking on road are

some of the examples of motion, visible to the eye. Motion of gas molecules is an example of motion, invisible

to the eye.

Rest & Motion are relative terms :

When we say that an object is at rest or in motion,then this statement is incomplete and meaningless. Basically, rest & motion are relative terms. An object which is at rest can also be in motion simultaneously. This can be illustrated as follows.

The passengers sitting in a moving bus are at rest with respect to each other but they are also in motion at the same time with respect to the objects like trees, buildings on the road side. So the motion and rest are relative terms.

Rectilinear motion :

If a particle moves in a fixed direction, the motion of this type is called rectilinear motion or one dimensional motion.For example the motion of an ant on a wire is a rectilinear motion.

Two dimensional motion :

If the motion of a particle is in such a way that its position remains on a fixed plane, then the motion of a particle is called two dimensional motion.