# Conceptual Approach - One Dimensional Motion - Part II

**What
is one dimensional motion?**

As all of you know that, to describe a location of a particle or object we need three coordinates i.e. x, y and z. The motion of a particle is said to be one dimensional if only one of the three coordinates of the particle changes with time. Or in simple terms, the motion of a particle along a straight line is one dimensional motion.

**What
is two dimensional motion?**

The motion of a particle is said to be two dimensional if only two of the three coordinates of the particle changes with time. The motion of a particle in a plane is a two dimensional motion i.e. two of the three coordinate’s changes with time.

**What
is three dimensional motion?**

The motion of a particle in space is generally three dimensional motion i.e. all of three coordinates change with time. The motion of a particle is said to be three dimensional motion if all the three coordinates of the particle changes with time.

**Define
Scalars and Vectors.**

Scalars: A physical quantity which is completely described by magnitude only is called scalar. Examples include time, distance, mass etc. Scalars quantities have only magnitude and no direction.

Vectors: A physical quantity which is completely described if we know its magnitude as well direction is called vector. Examples include force, velocity, displacement etc.

**How
would you describe a motion?**

In order to describe motion we need concepts of displacement, velocity and acceleration. All of these are vector quantities. Or we can say that a motion is described by displacement, velocity and acceleration.

**What
is distance?**

The length of the path travelled by a particle is called the distance travelled or covered by the particle. It is a scalar quantity and is measured in meters in SI units.

**What
is displacement?**

The shortest distance from the initial position to the final position of a particle is called displacement of the particle.

**Important
Point About Distance & Displacement**

Displacement can be positive, negative or zero while the distance travelled is always positive. When a ball is throw vertically upward and it comes down to initial point then the net displacement of ball is zero while the distance travelled by the ball is 2h where h is maximum height where ball reached.

**What
is average speed?**

The average speed of the particle is defined as the total distance travelled divided by total time taken i.e.

*Average speed =
total distance/total time taken*

SI Unit of average speed is m/s.

**What
is instantaneous speed?**

The speed at a particular instant is called as instantaneous speed.

**What
is average velocity?**

The average velocity of a particle is defined as the displacement divided by the time taken for the displacement. It is a vector quantity but we don’t consider vectors in one dimensional motion.

**Speed
vs. Velocity**

In our daily life we often use the words speed and velocity interchangeably. However, the two physical quantities are different in following manner: -

__Speed
is a scalar quantity and has magnitude only. However, velocity is a vector
quantity and has magnitude as well as direction.__

__Speed
indicates how fast something is moving whereas velocity tells us how fast and
in which direction it is moving. __

**What
is instantaneous velocity?**

The velocity at a particular instant is called instantaneous velocity. More precisely it is defined as the average velocity over an indefinitely short time interval.

**Difference
between uniform and non uniform velocity.**

*A
particle is said to move with a uniform velocity if it undergoes equal displacements
in equal interval of time, however small these time intervals may be. It should
be emphasized that when a particle moves with uniform velocity, the magnitude
as well as direction of the velocity remains constant*.

*A
particle is said to move with non uniform velocity or variable velocity if its
speed or direction or both change with time. In such case, we generally specify
average velocity of the particle. *

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