Velocity VS Speed : Brief Comparison
What Is Mechanics?
Velocity and Speed are one of the basic terms used in the world of Physics. Here we will learn about these scientific terms, but before that, we will have to take a dig at the subbranch of science which deals with the study of these terms i.e Mechanics.
The Mechanics is the branch of science that deals with the motion of physical objects. It means that all the science behind the movement of physically existing objects in this universe comes under the scope of Mechanics. For example, the motion of your car, the flight of an aeroplane or even the walking of a person will also be studied under the scope of Mechanics.
As I have said that the Mechanics deal with the motion of objects and when the motion of objects is considered the velocity and speeds are the first things to be learned. These terms are used to calculate the rate at which the moving object is changing its position with respect to some static point taken as reference in a given period of time.
Velocity
The Velocity is one of the basic terms used in the Mechanics branch of Physics. Here is the definition:
"Velocity may be defined as the rate of displacement of an object in the two or threedimensional space in a particular direction" or
"The velocity may also be defined as the rate of change of position of an object with respect to some static point or reference in a particular direction"
It is calculated by the formula Velocity = Displacement/Time taken
Here we have come to know about the term displacement. The displacement is the distance between the initial and final position of the object during the movement of the object.
For example, if you are driving your car in the straight forward direction and at time 10.00 AM your car is at point A(100 metres away from your initial position) and at 10.15 AM you reach at point B(1600 metres away from the initial position) as shown in the image given below.
The total displacement (the change in the position of the car) will be = Distance of point B from the reference point(refer image given below)  Distance of point A from the reference point(refer image given below)
= 1600  100 = 1500 metres
So total displacement = 1500 metres
Time taken by the car = (10 A.M. to 10.15 A.M.) = 15 minutes or 15x60 = 900 seconds
Applying the formula of velocity = Displacement/Time = 1500m/900s = 1.66 m/s(metre per second)
So the velocity of the car is 1.66 metre per second and if we want to calculate the same in kilometre per hour then we will have to take the time in hours and displacement in kilometres.
As we know 1500 metres = 1.5 kilometres
and 15 minutes = 0.25 hour
so the velocity will be = 1.5 km/ 0.25 hour = 6 km/hour
Please note that the velocity is a vector quantity so it has both the magnitude and direction.
Speed
We have learned about the term velocity in the previous section and now we will discuss about the speed. Here is the definition :
"The speed may be defined as the rate of covering the distance by a moving object in one unit of time"
There is no need for some reference point to be taken into consideration as we have taken in case of velocity.
For example, if you are driving your car with such speed that it is covering a distance of 20 metres in 1 second then its speed will be 20 metres/second.
It is worth noting here that the speed is a scalar quantity, therefore it has just the magnitude and no direction.
Difference between speed and velocity
Although the speed and velocity appear to be the same thing; there are differences, and now we will discuss the same. Both the speed and velocity are the units of measurement of the rate of change of displacement of an object. The difference is that the speed is measured without considering the direction of the movement while the velocity with the consideration of the direction of movement of the object.
Let's take an example of breeze flowing at the rate of 20 kilometres per hour in a direction 60° NorthEast to the horizontal axis line as shown in the image given below.
In this case, the speed can be easily calculated that is 20 km/hour.
So the speed of flow of wind is = 20 km/hour
When we will calculate the velocity of the breeze, we will have to take the following two things in the consideration:
 Reference point
 Direction of measurement
The reference point is the point of intersection of both the axis lines. The velocities will be different in different directions and we will calculate them as follows :
V(East) = Magnitude x Direction
= 20 km/h x Cos 60°(refer trigonometry)
= 20 km/h x 0.5
V(East) = 10 km/h
Similarly, Velocity in North direction:
V(North) = 20 km/h x Sin 60°(refer trigonometry)
= 20 km/h x 0.865
V(North) = 17.3 km/h
The breeze will hit the object in east direction with the velocity of 10 km/h and in the north direction with 17.3 km/h. So we can see that there is a difference in the velocity of an object while being considered in different directions but the speed will remain the same.
Velocity
 Speed


Velocity is a vector quantity
 Speed is a scalar quantity

It has both the magnitude and direction
 Speed has magnitude only and no direction

Velocity can be zero or negative
 Speed cannot be zero or negative

Velocity can be different in different directions for the same object
 Speed cannot be different in different directions for the same object

Scope
The speed is used to get an estimate about how fast an object is moving but the velocity is used to have an idea about the direction and magnitude of various forces making the object to move. For example, the speed of a moving car can be calculated by the revolutions per second of its tyres so it will indicate how fast the car is moving but the velocity will be calculated to find out the force required to maintain its movement in a particular direction and the momentum of the car as well(for study of unfortunate situations like accident or brakes failure etc.)
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.
© 2019 Sourav Rana
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