Definition of speed

The definition of speed is the distance an object travels in a given time. For instance, suppose one day it takes you 1 hour to walk to your favorite store that is 2 miles away from your house.

What is your speed? Your speed is 2 miles per hour.

At this pace, you are most likely not running. Any speed higher than 5 miles per hour may require some running.

If you decide to walk with a speed of 5 miles per hour, you might look funny to those looking at you.  

World's fastest man as of this writing is Usain Bolt because he covered a distance of 200 meter in just 19.59 second.

Let's us put this into perspective. This is a speed of about 23 miles per hour.

In reality, no man will be able to cover a real distance of 23 miles in an hour because of fatigue that can happen fairly quick. 

You may have noticed the frequent use of the word ' per ' by now.  The word per means " Divided by."

When we say 2 miles per hour or 2 miles per 1 hour, it is the same as  the following:

2 / 1

Since the number 2 is the distance and the number 1 is the time, we can also write:

d / t

We can then write the formula for the speed as shown below:

Speed =
d / t

Let's extend on the definition of speed by defining two more concepts.

Another definition of speed: Instantaneous speed

An object does not always do the same speed. When you walk, you walk faster or slower depends on what you want to achieve.

When you drive your car, you may do 50 miles per hour, 65 miles per hour, or even 5 miles per hour depending on traffic. What you see on the speedometer is your instantaneous speed or speed at that instant or particular time.  

The speedometer below shows instantaneous speed of 40 miles per hour when the time is exactly 8:45 AM and 30 miles per hour when the time is exactly 11:30 AM

Instantaneous speed

A great example of instantaneous speed is the speed recorded with a radar gun. The officer will come to you and say that you were doing 75 miles per hour, but the speed limit was 60. This was your instantaneous speed may be for a short period of time, sometimes just a few seconds.  

We have instantaneous speed because no one can maintain the same speed during the entire trip. Instantaneous speed can last 1 second, 2 minutes, or even 1 hour if you put the car on cruise control for 1 hour.

Average speed and average speed formula

Suppose you drive your car and you cover a distance of 110 miles in 3 hours. Then, you do another 50 miles in 1 hour. Finally, you cover 80 miles in 2 hours and you get to your destination. You may want to know what your average speed was since the speed varied during your trip. The formula to get the average speed is 

Average speed =
Total distance / Total time

Average speed =
110 + 50 + 80 / 3 + 1 + 2

Average speed =
240 / 6

Average speed  = 40 miles per hour

This concludes our lesson our the definition of speed.

Quiz about speed

This speed quiz will test your knowledge of speed, instantaneous speed, and the average speed.

Some questions will require that you use a paper and pencil.

My recommendation is to first read this lesson about the definition of speed and then take this quiz without using a calculator. 

Objective of the quiz:

  • Explore real life examples of instantaneous speed.
  • Identify the formula for speed.
  • Use the formula for speed and average speed to solve problems.
  • Identify the speed humans are most likely running.

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