Distance, Displacement, Speed and Velocity
Introduction
Kinematics is the science of describing the motion of objects using words, diagrams,numbers, graphs, and equations. Kinematics is a branch of mechanics. The goal of any study of kinematics is to develop sophisticated mental models that serve to describe (an ultimately, explain) the motion of real-world objects.In this lesson, we will investigate the words used to describe the motion of objects.Thatis, we will focus on the language of kinematics. The hope is to gain a comfortable foundationwith the language that is used throughout the study of mechanics. We will study such termsas scalars, vectors, distance, displacement, speed, velocity and acceleration. These words are used with regularity to describe the motion of objects. Your goal should be to become
very familiar with their meaning.
Mechanics : The branch of physics which deals with the study of force and motion their relatationship is called mechanics.The study of mechanics is divided into three parts.
i) Statics: the branch of mechanics which deals with objects at rest is called statics.
ii) Kinematics : Kinematics which is derived from a Greek word kinema meaning motion, is a branch of physics,the branch of mechanics which deals with the motion of objects onlywithout considering the cause of motion is called kinematics.
iii) dynamics: the branch of mechanics which deals with the cause of motion is calleddynamics.
Rest: A body is said to be at rest if it does not change its position with respect to thereference point. The objects which remain stationary at a place and do not change theirposition are said to be at rest.The position of a body with respect to surroundings does not change with time, the body is said to be in the state of rest.
Ex: A chair lying in a room is in the state of rest, because it doesn’t change its positionwith respect to the surroundings of the room.A tree, An electric pole, our house, our school....... etc.
Motion: A body is said to be in motion if it changes its position with respect to the
surroundings with the passage of time. All moving things are said to be in motion.All movingthings are said to be in motion.
Ex: A moving car, a moving train, a flying bird ...etc.
Rest and motion are relative terms : Rest and motion are relative terms. A body can be at rest as well as in motion at the same time.
For example, when a bus moves on a road, then the bus as well as the passengers sitting in it change their position with respect to a person standing on the road side. So the bus and the passengers sitting in it are in motion with respect to the person standing on theroad side. However, the passengers sitting in the bus do not change their positions withrespect to each other. It means, the passengers sitting in a moving bus are not in motion withrespect to each other. Ex : A person sitting in the compartment of a moving train is in the state of rest, withrespect to the surroundings of compartment. Yet he is in the state of motion, if he compares himself with surroundings outside the compartment
Scalars:The physical quantities which have only magnitude but not direction are called scalars.
Ex: Mass, length, distance, time, area, volume, density, work etc
Vectors: The physical quantities which have both magnitude and direction are called vectors.
Ex: Displacement, velocity, acceleration, force etc.