The speed at which a body moves is one of the most fundamental parameters within physics. In terms of linear motion, speed is defined as the distance traveled divided by the time taken. Bodies that rotate, such as wheels, use a different quantity to define rate of rotation. This is often the number of revolutions carried out per minute. It is straightforward to convert between revolutions per minute and linear speed.

Write down the linear speed in units of miles per hour. This example will use a car travelling at 70 miles per hour.

Convert miles per hour to meters per minute. To do this, multiply the number of miles per hour by 1609. Following the example, 70 miles per hour is equal to :

## Sciencing Video Vault

70 x 1,609 = 112,630 meters per hour.

Next, convert this figure to meters per minute. Since there are 60 minutes in an hour, divide the meters per hour by 60:

112,630 / 60 = 1,877 meters per minute.

Calculate the circumference of the wheel. Use the formula: c = 2_pi_r, where c is the circumference, r is the radius, and pi can be approximated by 3.14. Following the example, if the car wheel has a radius of 0.3 meters, then the circumference is equal to:

0.3 x 3.14 x 2 = 1.89 meters.

Calculate the wheel speed in revolutions per minute. To do this, use the formula:

revolutions per minute = speed in meters per minute / circumference in meters.

Following the example, the number of revolutions per minute is equal to:

1,877 / 1.89 = 993 revolutions per minute.