The speed and velocity of an object are often confused as the same quantity by a lot of students, but they do have some underlying differences. The speed of an object is measured in terms of distance, which is a scalar quantity.
However, the velocity is measured in terms of displacement, which is a vector quantity. To understand what is Speed & velocity and this difference in a more elaborate fashion, we will take a look at these concepts in this article.
What Is Speed
Speed is the rate of change of distance of a moving object. It is a scalar quantity. As speed is a scalar quantity, it is directionless and has only magnitude. The formula of speed is distance time or d/t. The standard unit of speed is a meter per second.
What Is Velocity
Velocity is the measurement of the rate of change of displacement. It is a vector quantity, which means that it has both magnitude and direction. The unit of velocity is the same as that of speed. The standard unit of velocity is meters per second. The formula of velocity is – change in the displacement change in the time
or x/t, where delta denotes the relative change in the value of the quantity.
Suppose a person is moving in a circular path, where they return to the starting position. This may be considered as some activity, but during this activity, the velocity of that person will be zero. This is because, in the end, that person comes back to the point where he/she has started, and thus there is no change in the value of displacement.
Hence, the velocity of that person becomes zero.
A Comparative Study Between Speed And Velocity
| Serial No | Category | Speed | Velocity |
| 1. | Definition | It is the rate of change of a body in any direction | It is the rate of change of displacement of an object in a particular direction. |
| 2. | Quantity | It is a scalar quantity | It is a vector quantity |
| 3. | Magnitude | The value of speed can never be zero or negative | Velocity can either be negative or positive. Its value can also become zero. |
| 4. | Direction Of Motion | If the body changes its direction, the average speed of that body will be still counted. | If a body changes its direction, velocity will not be counted because the “ velocity of the object changes with the change in direction”. So the velocity of an object can be only in one direction. |
| 5. | Standard unit | It is measured in meters per second, i.e., m/s.
Commonly it is measured in km/hr. |
Velocity can also be measured in meters per second or km/hr. However, velocity also carries a vector sign with it to indicate direction. |
| 6. | Formula | Speed = distance/ time or d/t. | Velocity = x/t, where is delta. In this, x denotes the change in displacement, and t denotes the rate of change of time. |
Types Of Speed
There are different types of speed which are as follows –
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Instantaneous Speed
When a body is moving at different speeds, then at any instant of time, the speed of that particular body is called instantaneous speed.
We can find this speed on the speedometer of our vehicles. Mathematically, it is said to be “the magnitude of instantaneous velocity that is the derivative of position concerning time”.
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Average speed
Average speed is the total distance travelled by a body in a particular period. To calculate the average speed, you can divide the total distance covered by an object by the total time taken by it to cover this distance.
Hence, the formula of average speed is
Average speed = Total Distance/ Total time taken
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Rotational speed
The rotational speed of a body, which is rotating along an axis, is calculated by dividing the number of turns made by it by the total time taken by the object. The rotational speed is measured as revolutions per minute, cycles per second, or radians per second.
Rotational speed = Number of rotations/ Total time taken
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Uniform speed
If a body covers an equal distance at an equal interval of time, then the speed by which that particular object is moving is called uniform speed. Uniform speed is indeed a hypothetical concept, and such conditions cannot be achieved in reality because a lot of external factors can also affect the speed of a vehicle.
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Relative speed
Relative speed is a term used to compare the speeds of two moving objects. The relative speed of two bodies travelling in opposite directions is the sum of their speeds.
Thus, the formula of relative speed becomes,
Relative speed = S1 plus S2, where S1 is the speed of the first body and S2 is the speed of the second one.
When both the bodies move in the same direction, the relative speed will be the difference in their speed.
Relative speed = S1 – S2.
Types of Velocity
Just like speed, velocity can also be classified into various types.
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Tangential Velocity
It is the velocity of a body that is travelling in a circular path. If the tangent on any point on its path indicates the direction of the object, so its tangential velocity is a product of the angular velocity and the radius of the circular path of the object.
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Instantaneous Velocity
The velocity of an object at any instant of time is called its instantaneous velocity.
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Uniform And Non-Uniform Velocity
When there is an equal displacement of a body at an equal interval of time, the body is moving with a uniform velocity. Whereas, if there is an unequal displacement of the body over an equal period of time, it is travelling with a non-uniform velocity.
Key Things To Remember
The key difference between speed and velocity is that speed is a scalar quantity, whereas velocity is a vector quantity. This means that while calculating speed, you will be finding the rate of change of ‘distance’, whereas, while calculating velocity, you will be calculating the rate of change of ‘displacement’.
Speed and velocity can be classified into various types. One thing that makes both of them similar is that they both have the same SI unit, i.e., m/s or km/hr.
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