the Most Important Equation in Physics

Use Newton's second law

= 10 Newtons/kilograms = 10 (kilograms meters/second

= 10 meters/second

When an object moves in a straight line, such as a rock falling vertically, the acceleration is the change in speed per unit time. Hence, the little computation above tells us that the rock increases its speed at 10 meters/second each second. If the rock is initially released without being thrown, its speed starts out as zero. After one second, its speed becomes 10 meters per second, after two seconds its speed reaches 20 meters per second, after three seconds it is 30 meters per second, and so on. The rock is accelerating at 10 meters/second

One can also determine how far such a rock falls. The distance an object travels is the average speed

= (5 meters/second) (1 second) = 5 meters .

How fast does it travel during the first two seconds? The rock's speed at two seconds is 20 meters/second while its initial speed was 0 meters/second. The average of these two speeds is 10 meters/second. So in two seconds, the rock drops

= (10 meters/second) (2 seconds) = 20 meters .

For the case of three seconds, the rock's average speed is 15 meters/second (the average of 0 meters/second and 30 meters/second). So in three seconds, it falls

= (15 meters/second) (3 seconds) = 45 meters .

Note that the rock is falling by successively larger amounts because the speed is continually increasing. The above computations of the distance that the rock falls can be summarized by the formula

and, indeed, this equation provides the result for any time

It turns out that when air friction is negligible, all bodies fall with the same acceleration at the surface of the Earth. This acceleration, which is almost 10 meters/second

Use Newton's second law

= 19500 kilograms miles/hour/second

The units are mixed in the above calculation. To convert to Newtons, one needs to convert hours to seconds and miles to meters. One mile is about 1610 meters and one hour is 3600 seconds. So

19500 kilograms (1610 meters)/(3600 seconds)/second = 8700 Newtons

This force is more than 40 times the force that the rock in example (1) feels due to the gravity of Earth.

To the top of this file.

To the famous equation page.

This webpage was prepared by Stuart Samuel, who has given Jupiter Scientific Publishing permission to use this page and who is the spokesperson for

This web page may NOT be copied onto other web sites, but other sites may link to this page.

Copyright ©2000 by Stuart Samuel

To Jupiter Scientific's Information Page