IIT JEE Blogs

• Imagine flying birds, moving planets, gushing air, flowing water and so on, all these phenomena are happening around us continuously. All the above mentioned phenomena can be summarized in one word “motion”.
• When something moves, there are several factors, which can be observed. If it moves, it will cover some distance, the distance covered may be different in different time periods. It may be moving slow or fast. Further its speed or velocity may be changing with time. All these factors depend on each other and we need to study their relationships.             Various kinds of motion can be systematically grouped under few broad categories. The point of distinction is made on grounds of the velocity vector. On these grounds motion can be:
• one dimensional, where only one dimension is required to describe the motion
• two-dimensional, where we require two dimensions to describe the motion of the particle
• three-dimensional, where three dimensions are required.

Pre-requisite

State of Rest and Motion

• If the position of a particle is changing with respect to its surroundings in a given time interval, we say the particle is in motion and on the other hand if the position particle is not changing with respect to its surroundings, we can say the particle is at rest.

Position

The position of a particle refers to its location in the space at a certain moment. A vector joining the moving particle with the origin can describe the position of that particle at a particular moment.

Displacement

It is the vector joining the initial position of the particle to its final position in a given time interval.

Velocity

The rate of change of position of a moving particle is known as its velocity.

Acceleration

The rate of change of velocity with time is called the acceleration.

Distance and Displacement

• To understand the difference between distance and displacement, we study the motion of vertical throw of a ball with respect to point O to height h.
• After some time it will come again to the same point O. The displacement of ball is zero but there is some distance traversed by the ball. It’s because distance is a scalar quantity but displacement is a vector quantity.

Speed and Velocity

• Speed is the rate of change of distance without regard to directions. Velocity is the rate at which the position vector of a particle changes with time. Velocity is a vector quantity whereas speed is scalar quantity but both are measured in the same unit m/sec.