In our physics classes, we were all exposed to many terms such as inertia, gravity, speed, velocity, and so on. These terms are used to quantify various things, and they all have associated formulas.
So, today we’ll go over some points about speed and velocity. You’re probably wondering what speed and velocity mean, what the formulas are, and how they differ from one another.
Speed:
The distance covered by an object in unit time is called average speed.
Velocity:
The displacement of an object per unit time is called average velocity. Average velocity is a vector and is along the direction of displacement.
Example:
A train named Godavari express starts at 5.00 pm from Visakhapatnam and reaches Hyderabad at 5.00 am the next day.
Let the distance of the entire trip from Visakhapatnam to Hyderabad be 720km. The Journey time is 12 h. What is the distance covered by the train in each hour?
It is equal to 720km/12h = 60 km/h
Can you say that the train has covered exactly 60 km in each hour?
Obviously, the answer is NO, because there may be some variations in distance covered by the train each hour. So we take the average of distances covered by the train for each hour to decide its average speed. We know that the distance covered by the object in unit time is called average speed.
Average speed = total distance / time taken
Let the displacement of the trip in the above example be 360 km due south-west. What is the displacement in each hour?
The displacement per hour = 360km/12h south-west
= 30km/h south-west
The displacement of an object per unit time is called average velocity. Average velocity is a vector and is along the direction of displacement.
Average velocity= displacement / time taken
The quantities average speed and average velocity explain the motion of a body in a given time interval. They do not give any information about the motion of the body at a particular instant of time.
Difference Between Speed and Velocity:
| speed | velocity |
|---|---|
| Definition | |
| The distance covered by an object per unit time | The displacement of an object per unit time. |
| Formula | |
| Average speed = Total distance / Time taken | Average velocity= Displacement / Time taken |
| Positive/ negative | |
| The speed of a moving object cannot be negative. | The velocity of a moving object can be negative, positive as well as zero. |
| Quantity | |
| It is a scalar quantity | It is a vector quantity. |
| When can/cannot be zero | |
| The average speed of a moving object cannot be zero | The average velocity of a moving object can be zero when displacement=0 |
| Rapidity of motion | |
| It gives ideas about the rapidity of motion object. | It gives ideas about the rapidity of motion and also the direction of the object. |
Bottom line:
So when we compare, If the object is moving in a straight line, then its speed and velocity will be the same. Thus it is said that speed and velocity are distance-time graph and gradient of displacement time graph respectively.Â
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