# Kinematics (1D) I – Introduction to Basic Ideas

Here we are in this world filled with amazing phenomena and activities that we observe every day. For example, we notice airplanes, cars, birds etc. One common thing among them is that they are all examples of motion. What is motion? What causes Motion? How do we study it? Are there types of motion? These questions will be answered in this series on Kinematics.

#### What is Kinematics?

The reasons that explain why or how a particle is in motion are many. When a particle is in motion then the study of that particle under observation is called kinematics.To understand this branch of physics we should be having a very good idea of what is meant by motion, rest, and Frame of reference.

First, if we talk about motion in the simplest of terms, then the change in position of a particle with respect to time is motion. Everyday objects are“extended” objects, meaning they have dimensions or volume. But in kinematics, we treat a large collection of particles or everyday objects as a single point mass. Meaning we treat the body as a single particle. Therefore, it becomes is easier to define and study the motion of that particle.

Let us understand the above by an example. When a ball is rolling on the ground then the ball is in motion. But when the ball is not moving, it is considered to be at rest.  The ball is treated as a point mass. Why? Because the ball is made up of infinitely many particles which are randomly in motion. It is hard to study the motion of all these particles individually.

#### Coordinate system and motion along an axis

The position of a particle is represented using something called the coordinate system. The coordinates of a particle can be represented on a 1 dimensional line, a 2 dimensional plane or a 3 dimensional space. The coordinates (position) of a particle in space are represented using three variables – x, y and z. the position of the observer is usually the origin (where x, y and z, all are 0). the position of the object being observed is given relative to the observer.

Motion is always defined with a comparison between a observer and source. it is compared to the position of observer and the speed of the observer (relative velocity comes into play when both are in motion). When a particle is in motion it can perform 1-D,2-D and 3-D motion. In kinematics, we generally deal with the motion of particle in 1-D which can be understood as the motion along either x or y axis on the co-ordinate system.  This is linear motion – either left and right or up and down. in daily life we come across such type of motion frequently.

#### Atoms and coordinates

When we study a particle at atomic/molecular level, we see that particles (electrons or atoms in this case) have equal probability or tendency to move along x,y and z axis. It has equal chances to move in all the 3 directions these atoms or small particles are capable of performing 3-D motion. A 3-D co ordinate system is very useful to determine the position of a particle in space.