# average speed

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### noun

the total distance traveled divided by the total time elapsed.

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## Words nearby average speed

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

## HOMEWORK HELP

### What is average speed?

Average speed is calculated by dividing the total distance that something has traveled by the total amount of time it took it to travel that distance.

Speed is how fast something is going at a particular moment. Average speed measures the average rate of speed over the extent of a trip. Average speed is usually applied to vehicles like cars, trains, and airplanes. It is often measured in miles per hour (mph) or kilometers per hour (kph).

Average speed is used in all kinds of fields, including physics, astronomy, and transportation.

### How to find average speed

Let’s slow down and start with an example. If you were to drive 200 miles in two hours, you could calculate your average speed by dividing the total distance (200 miles) by the total amount of time it took (two hours), giving an average speed of 100 miles per hour. (Which means the next thing you’re going to have to calculate is how to pay the speeding ticket.)

Average speed might seem like a basic, obvious concept, but for much of history, people didn’t have much of a practical need for such a calculation (plus there were no speedometers on horses). In the 1600s, physicist and astronomer Galileo Galilei tried to calculate the speed of light by measuring how long it would take a person to see a light from across a field. It didn’t work (light is way too fast to be measured this way), but Galileo did come up with the formula distance/time = average speed. (Others probably discussed the concept before that, but Galileo usually gets the credit.)

Average speed should not be confused with instantaneous speed, which measures the speed of an object at a specific instant in time. Instantaneous speed is a physics term. In everyday life, we just call this speed, which is what the speedometer in your car tells you—exactly how fast you’re going at that moment. Speed is sometimes confused with velocity, but they are not the same. In physics, velocity measures something’s speed relative to its direction of motion.

In practical situations, average speed usually comes up in the context of transportation, such as the average speed of a train or airplane during a trip.

### Did you know ... ?

Light has an average speed of approximately 186,000 miles (about 300,000 kilometers) per second.

### What are real-life examples of average speed?

Average speed is used in physics and other scientific fields, but it’s also used for all kinds of practical applications, especially in transportation. The software that runs your GPS (Global Positioning System) app uses average speed to calculate how long a trip is going to take.

### Quiz yourself!

True or false?

Average speed and average velocity are different measurements.

## Example sentences from the Web for average speed

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