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Speed

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Author:
Nathan Lampson

This lesson will explain what speed is, including the difference between average speed and instantaneous speed, showing how to calculate both. It will also show the common units used to represent speed.

Tutorial

When objects travel a distance during a certain amount of time, the rate of travel of the object is called the object's speed. Speed is commonly expressed as meters per second (m/s) or kilometers per hour (km/h).

The speed of an object can be calculated with the equation:

Speed=Distance/Time

Example:

If a car is car travels a distance of 60 meters after driving for 3 seconds, what is the cars speed?

Distance=60 meters (m)

Time=3 seconds (s)

Speed=Distance/Time

Speed=60m/3s

Speed=20 m/s

Average speed is a measurement used to calculate the speed of a moving object that isn't moving at a constant rate. To calculate average speed, divide the total distance traveled by the total time an object is in motion.

Average Speed=Total Distance/Total Time

Example:

A car travels a total distance of 600 kilometers over the course of 6 hours, what is the average speed of the car?

Total Distance=600 kilometers

Total Time=6 hours

Average Speed=Total Distance/Total Time

Average Speed=600 km / 6 h

Average Speed=100km/h

Instantaneous speed is a measurement that is used to calculate the exact rate an object is moving at a given time.

Calculating instantaneous speed of an object is very difficult. If a race car completes a race with an average speed of 140km/h, the instantaneous speed of the race car at the end of the race will be faster than 140km/h. When the race car begins the race, it will be traveling at very low speeds. At the end of the race, the race car will be traveling much faster.

Instantaneous speed can be estimated by calculating the average speed of an object over a very short time. For the race car, finding the average speed of the car during the last few seconds of the race can give a better idea of the instantaneous speed of the car at the end of the race.