Basic Physics lesson-1 : Distance and displacement
Physics is the branch of science in which we study about the nature and properties of material and energy and for all such things formula of Physics are derived for calculation purposes. Physics is deeply related to Mathematics and Chemistry and together threse three subjects make a robust scientific understanding. This is the first article in the series and in this series we will try to understand the basic Physics and its applications. In the present article we will try to learn the distance and displacement. So this is a beginners course but might also interest the science students and scientists to revise their basic concepts.
What do we understand by distance?
When someone says that he or she has walked a distance of 5 km today, what does it mean to us? It simply tells us that he has walked from one place to another whatever path he has chosen among the streets or lanes or may be many rounds in a big park or playground. Whatever path, a straight line or zig-zag one he has followed, the net result is that he has walked a total of 5 km. Can we say in which direction he walked? No, he went sometimes in one direction and sometimes in another so we do not know the direction. It was changing during the course.
So, we know the length of the path he had traversed during his walk and it was 5 km. In Physics, we call such quantities as scaler quantities. They do have a value but do not have a direction.
What do we understand by displacement?
What happens when we add an element of direction to it? Then it becomes a vector quantity. Ler us understand it better with the example of the person who walked 5 km on that day. Let us see how he went on. Suppose in the first leg of his walk he walked 200 m in an Easterly direction. Now this distance of 200 m has got a direction element attached to it. In Physics we call such quantities as a vector - they have a value as well as direction. So this distance of 200 m is known in Physics as a displacement of 200 m in East direction. I can represent it as a line drawn to the scale in East direction. For understanding purpose we put an arrow at the end of it to show the direction which is of course towards East in this particular case.
All the part distances walked by a person in a particular direction can be treated as a displacement vector and can be represented with a value and direction. So the path traversed by him will be a sum of so many vectors annexed with one another.
Let us extend the same example now. As we know that the person first walked 200 m in East direction. Now let us assume that after that he walked 300 m in North-East direction and completed some work there and then went a distance of 400 m Southwards. We can show these three displacement as vectors (diagram-1).
Application - example
Once we understsnd the notion of displacement then we can use it in solving different types of problems related to displacement. Let us take the above example and extend it further. Let us give the names to the different points along his walk.
So the person has already gone 200 m from point A to B in East direction and then 300 m from B to C in North-East direction and then walked 400 m from C to D in South direction. Now let us assume that he further walks 100 m from D to E in West direction to a cafeteria for a cup of coffee.
The problem is to find where the cafeteria lies with respect to the point A from where he started.
To solve this problem one has to draw the displacements on a scale and measure the distance of the point E from A on the same scale and the exact direction can be found with a compass. I have drawn it and found that displacement AE has a value of 365 m and is almost in a South-East direction of the starting point A. The solution is given in diagram-2.
Though the person has walked a total distance of 200 + 300 + 400 + 100 = 1000 m but his displacement from the starting point A is only 365 m.
Distance is a scaler quantity and tells the total length of the path traversed while displacement is a vector quantity which specifies a value and its direction.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2020 Umesh Chandra Bhatt