Average vs Instantaneous Speed: Difference and Comparison

Kinematics is the branch of science which deals with the cause of the motion of any object. Kinematics is also referred to as the geometry of objects. It is an important branch of physics. It deals with the forces, motions, etc., which cause an object to move, rotate, oscillate, etc., from its place.

Key Takeaways

1. Average speed is the total distance travelled divided by the total time taken, while instantaneous speed is the speed at any given moment.
2. Average speed is a measure of overall speed during a journey, while instantaneous speed is the speed at a specific point in time.
3. Average speed is lower than instantaneous speed unless the speed is constant throughout the journey.

Average Speed vs Instantaneous Speed

Average speed is the distance travelled by an object over a given time interval, divided by the duration of that interval. Instantaneous speed is the rate at which an object moves at a particular moment without considering any distance travelled before or after that moment.

Average Speed is a constant value and is measured by calculating the speed of an entire trip or journey. For a journey, the body or an object doesn’t need to remain at the average speed.

Sometimes, it may have more value than the average speed or less value than the average speed depending on the path and hurdles.

Instantaneous speed is not constant for an object or a body. And it is measured with the help of the vehicle-installed speedometer. The speedometer tells the exact accurate value of the speed at that particular instant of time.

The value of the instantaneous speed is greater than or equal to zero. Also, instantaneous speed is a scalar quantity.

Comparison Table

Parameters of Comparison	Average Speed	Instantaneous Speed
Definition	It is defined as the total distance traveled divided by the total elapsed time.	It is defined as the speed at a particular instant of time.
Formula	Total distance / Total time	The distance at that instant / Time at that instant
Meaning	Measured by calculating the speed for an entire journey	Measured with the help of a speedometer
Constant	It is constant	It is not constant
Example	A bike traveling with a speed of 40 miles/hour; thus, the average speed is 40 miles in an hour.	A bike traveling at a certain speed at an instant of time can be given by a speedometer.

What is Average Speed?

It can be defined as the total distance travelled by the object or a body divided by the total elapsed time. The formula for calculating the average speed is given below –

Average Speed = Total distance travelled by the object / Total time taken by the object.

It can also be measured by calculating the speed of the entire journey or trip. It is believed that the average speed of an object or body is constant.

While travelling in a vehicle, it is quite difficult to keep the vehicle at a constant or uniform value because of the uneven structure of the road’s brakes need to be applied, which slows down the vehicle.

Thus, the body’s speed is not constant, and the distance travelled divided by time gives us the object’s or body’s average speed during that time.

Consider the given example – If a body or an object travels a distance of 100 km in 4 hours, the average speed is 25 Km/hour. It does not mean that the body is moving at the same speed throughout the journey.

When the road is straight, flat, and free, the speed of the vehicle may be above the average speed, but on a curved road, hills, or in a crowded area, the speed may be slower than the average speed value.

What is Instantaneous Speed?

Instantaneous Speed can be defined as the speed of a body or an object at a particular instant in time. The formula for calculating instantaneous speed is given below –

Instantaneous Speed = The distance at an instant / Time at that instant

Instantaneous Speed can be measured with the help of a speedometer and is believed to be never constant. The instantaneous speed of an object or body is always greater than or equal to zero. It is considered a scalar quantity because it does not have a specific direction of motion.

For a uniform motion, instantaneous speed is considered a constant value. But for a particular given time, instantaneous speed is the magnitude of instantaneous velocity at that time. It is a limit of the average speed as the time interval becomes very small.

Main Differences Between Average Speed and Instantaneous Speed

1. The average speed of an object or a body is stated as the total distance travelled by the object or a body divided by the total elapsed time, while the Instantaneous Speed of an object or a body can be stated as the speed of an object or a body at a particularly given instant of time. 
2. The formula for calculating Average speed mathematically is the Total distance covered by the object or body / Total time taken by the body or object, while the formula used to calculate instantaneous speed mathematically is the distance at a given time / Time at that instant.
3. The average speed of the object can be measured by calculating the speed of the entire journey, whereas a speedometer helps to calculate the instantaneous speed of a given object or body. 
4. The average speed of an object is constant, while the Instantaneous speed of an object is not constant.
5. An example of Average speed is when a person is moving at a constant speed of 50 miles/hour, as average speed is the rate of change in the speed concerning time; thus, there is no change in the speed; therefore, the average speed is 30 miles per hour while considering an example for Instantaneous speed is that the speed of the object while travelling changes concerning that instant time thus it varies and can be measured by the speedometer. 

References

1. https://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-947X(2002)128:2(182)
2. https://ieeexplore.ieee.org/abstract/document/148453