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Physics 1 | English Medium

Physics is a really easy and an enjoyable subject once you get hold of it. But you have to remember that not just listinig to the teacher and reading physics note is not enough for you to master O/L physics, you have to practice doing problems again and again. Now lets get to the lesson.

1.) Firstly lets iunderstand the different between the two terms 'Distance' and 'Displacement'.

In the diagram shown above there are three lines drawn between the points A and B. Out if them the black line is a straight line while the brown and the green lines are two randomly drawn lines connecting A and B.
Now consider drawing a line between A and B such that the length of that line is equal to the shortest distance between A and B, you will realize that line is non other than the black line itself. All the other lines that connect A and B are lnger than the one and only straight line that can be drawn connecting A and B. That straight lines length or in other words the shortest distance between two points is called the displacement betwwen them!


In summary Displacement is the shortest Distance between two points. Distance is  the length of any of the curved lines drawn between two points.

Now lets look at the the characteristics of Distance and Displacement


The quantities (measurements) taken when we study physics are called physical quantities. There are two types of physical quantities mainly.
1.) Vector quantities
2.) Scalar quantities

Vector quantities have a magnitude and a direction whereas scalar quantities only have a magnitude and no well difined direction.

Distance is a scalar quantity while Displacement is a vector qunatity. So it goes without saying when you answer a question which is about the concept of Displacement you should keep in mind to answer it with both the magnitude and direction.
Now the next thing is how do you state the direction of a displacement given? In physics the to define a direction we need two points. For an example if a man walks from town A to town B on a straight line drawn between them, if the shortest distance between the town is 50km, his displacement can be stated as, 50km to thee direction of AB. Another way of stating direction is using the direction map of  a compass, meaning you state the direction as North, South,..... or 15 degrees from North to East, 12 deggrees from South to West which is covered in O/L Maths.

Next we will learn the graphical represantation of a vector.
A vector is represented by a straight line with an arrow head. The length of the line should be directly propotional to the magnitude of the vector while the arrow should point to the direction of the vector.
The SI unit for Displacement is meters, 'm' .

2.) Now lets understand the concepts of Speed and Velocity.

Speed is a scalr quantity and Velocity is a vector quantity, meaning Speed does not have  a well difined direction while Velocity does. As an example when the direction of a moving object change which is goin on 25km per hour it has a constant Speed of 25km per hour but it does not have a contant Velocity because its direction changes.

Speed and Velocity are difined as below (simplified for O/L level),

Speed = Distance/ Time taken

Velocity = Displacement/Time taken

The SI unit for Velocity is meteres per second, 'ms-1'.

Written by : Uncle

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2 දෙනෙක් අදහස් කිවුවා:

වකා - WAKA said...

Great!!

ආගන්තුක යා said...

Thankx Waka
(behalf of Uncle)

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