Motion in a Straight Line

Explore the fundamentals of Kinematics with a deep dive into motion in one dimension, commonly known as straight-line or rectilinear motion. This segment of physics focuses on the movement of particles along a single axis, providing insights into key concepts such as the position vector and displacement vector, along with the differences between displacement and distance.

In this comprehensive guide, we will explore:

• The essence of motion along a straight line
• Understanding the position of a particle in linear motion
• The concept of particle displacement
• Distinguishing between distance and displacement

Introduction to Motion in one dimension

When we say an object is undergoing motion along a straight line, it can be in any direction as long as it is straight. It can be horizontal, vertical or slanted. Also, any moving object is shown as a particle or a point object. The branch of physics where we study the path of a motion including position, velocity, acceleration etc. is called kinematics.

Position of a particle

The position of a particle is always measured relative to the origin. If the object is on the positive side of the X axis, it is considered a positive position and if it is on the -ve side of the axis, the position is considered a negative position. Also position is a vector and it has magnitude and direction.

Displacement of a particle

Often written as delta x is measured as the difference between the final position and the initial position. Displacement is a vector quantity and so a positive number indicates movement or displacement in the positive direction of X axis and a negative number indicates displacement in the in the negative X direction. So the number indicates the magnitude of displacement, and the sign indicates the direction of displacement.

Magnitude of displacement vs. distance

The absolute value of displacement is always the length of the line connecting the initial point and the final point.. in other words it is the shortest distance between the two points. Distance however is the length covered when moving between the initial and the final position. Distance is a scalar quantity and has magnitude only and no direction.

So displacement and distance are two different measures and the differences between distance and displacement is as has been explained the paragraph above