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Speed and Velocity are two terms that we often use interchangeably. These terms are used to explain the motion of an object. For us, the meaning of both the terms is somewhat the same.
But, physics has something else to say. Both mathematics and physics say that both of these terms are very different and have their unique properties. In this article, we will tell you the meaning and key differences of speed and velocity.
Definition of Speed:
Speed is the amount of distance covered by an object over a specific period. It does not consider the direction in which the object was travelling. It is helpful in estimating how fast the object is moving. Since it doesn’t take the direction of the object into consideration it is called a scalar quantity.
A change in speed tells us two things: either the object’s speed has gotten very fast or slow. Increase in the speed of an object is called acceleration. On the other hand, if the speed decreases it is known as deceleration. If the object is not moving at all the speed is zero.
Mainly there are 3 units of measurement for speed:
- meters per second (m/s) (This is the SI unit for speed)
- kilometers per hour (km/h)
- miles per hour (mph)
Formula for Speed:
r = d/t
where,
r: rate or speed,
d: distance covered by the object,
t: time taken by the object to complete the movement.
As you can see the formula helps us in understanding the average speed of an object over an interval of time. The speed of the object may have gotten faster or slower at different points during the time interval but, using this formula we get the average speed.
This formula of speed can be arranged in 2 different ways:
- d = s × t
- t = d/s
To calculate the value of one variable we must know the value of the other two variables.
Definition of Velocity:
Velocity is the rate at which a particular object changes its position in a certain direction. In order to find velocity, we need both magnitude and direction. Velocity is a vector quantity.
At its core, velocity tells the difference between an object’s final and initial positions. In terms of calculus, velocity indicates the first derivative of position with respect to time. It is extremely important to understand velocity.
Velocity helps us to determine how quickly a person or an object will reach its destination from a given location.
Formula for Velocity:
v = d/t
where,
v: velocity
d: displacement
t: total time taken by the object to cover the distance
The SI unit of velocity is meter per second (m/s). The formula of velocity tells us the rate of change in displacement with respect to time. Now, you may ask what is displacement? In simple words, displacement is the difference between the ending and starting positions of an object.
Since displacement takes magnitude and direction into consideration it is a vector quantity. There will be zero velocity if there is no displacement in the object’s position and if the object has not covered any distance.
Constant Velocity V/S Acceleration:
For an object to have constant velocity it must satisfy one condition: move at a constant speed in a straight line. Even if an object is satisfying this condition i.e. it moves in a straight line but changes its directions frequently it won’t have a constant velocity. Let’s understand this with a simple example.
A car which has a constant speed of 25 kilometres per hour moving in a circular path will have a constant speed. But, it won’t have a constant velocity since it is constantly changing direction. Here, the car is undergoing an acceleration.
Difference between Speed and Velocity:
| Speed | Velocity |
| Meaning | |
| Speed is the amount of distance covered by an object over a specific period of time | Velocity is the rate at which a particular object changes its position in a certain direction |
| Quantity | |
| Since, speed doesn’t take magnitude and direction into consideration it is a scalar quantity | Since it takes magnitude and direction into consideration, it is a vector quantity |
| Magnitude | |
| It can be zero, negative, or positive | It can never be negative or zero |
| SI Unit | |
| The SI unit of speed is meters per second (m/s) | The SI unit of velocity is meter per second (m/s) |
| Change of Direction | |
| Even if the direction is changed the average speed will continue to count | The velocity will change if the direction of the object changes and that’s why the object must follow one direction |
| Interrelation | |
| Most of the time speed may or may not equal velocity | An object can have different velocities but the rate of speed would be the same |
Conclusion:
As you can see both speed and velocity have their own unique properties and are very different from each other. The only thing you need to remember is that speed doesn’t take the direction of the object into consideration.
While velocity is the rate at which a particular object changes its position in a certain direction. Both of them are used extensively in physics and have endless applications. We hope that whenever someone uses the words speed and velocity you will better understand what they are saying.
