Instantaneous Speed: Definition, Formula & Example

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  • 0:00 What Is Speed?
  • 0:44 Instantaneous vs Average
  • 1:40 Examples
  • 3:03 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll learn about instantaneous speed, the difference between it and average speed, and the formulas for calculating both of them. Examples will be provided, and a quiz will let you test your understanding.

What Is Speed?

As you're sprinting on the track getting your daily exercise, a plane zooms overhead. Cars fill the street, some speeding along, other stuck in traffic. Your friends wander over to the track, waiting for you to finish exercising so you can take the bus home together. What do all these daily occurrences have in common? The answer is speed.

Speed is how fast something is moving, and things in the world are frequently moving. In fact, Earth itself is always moving, although this isn't apparent in our daily lives.

There are two ways we can measure how fast something's moving:

  1. By calculating instantaneous speed
  2. By calculating average speed

Let's explore how these two measurements are different.

Instantaneous vs. Average

When a cop pulls you over for speeding, she clocked your car's instantaneous speed, or speed at a specific point in time as your car sped down the road. 'Instantaneous' comes from the word 'instant' meaning only one specific moment.

This is different than your average speed from the trip, which takes into account how long it took to complete the entire journey and the distance traveled. Be careful, measuring average speed assumes you moved at about the same speed the entire trip.

To calculate instantaneous speed, we need to divide part of the total distance traveled by time. However, we don't want to use the distance of the entire trip, because that will give us average speed. We use a small distance of the trip. The smaller the distance used, the more accurately we can measure the speed for that specific time.

Let's look at some examples to make this concept more clear.


Let's suppose it's a snowy day. You're in a Boeing jet at a New York City airport, taking a trip to Chicago. Your plane is taxiing down the runway when it suddenly stops. There will be a delay as the plane is de-iced for air travel. This adds an extra hour onto your journey.

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