GRAVITATIONAL ACCELERATION AT SEA LEVEL
 

The term acceleration can be somewhat confusing to the uninitiated when it is used in reference to gravitation. Isn’t gravity just a force that pulls on things? The answer to this question is both yes and no. Obviously, gravitation pulls things downward toward the center of the Earth. If you were on another planet, you would find gravitation there, too, but it would not pull on you with the same amount of force. If you weigh 150 pounds here on Earth, for example, you would weigh only about 56 pounds on Mars. (Your mass, 68 kilograms, would be the same on Mars as on Earth.) Physicists measure the intensity of a gravitational field according to the rate at which an object accelerates when it is dropped in a vacuum so that there is no atmospheric resistance. On the surface of the Earth, this rate of acceleration is approximately 9.8067 meters per second per second, or 9.8067 m/s2. This means that if you drop something, say, a brick, from a great height, it will be falling at a speed of 9.8067 m/s after 1 s, (9.8067 × 2) m/s after 2 s, (9.8067 ×3) m/s after 3 s, and so on. The speed becomes 9.8067 m/s greater with every second of time that passes. On Mars, this rate of increase would be less. On Jupiter, if Jupiter had a definable surface, it would be more. On the surface of a hugely dense object such as a neutron star, it would be many times more than it is on the surface of the Earth.
The rate of gravitational acceleration does not depend on the mass of the object being “pulled on” by gravity. You might think that heavier objects fall faster than slower ones. This is sometimes true in a practical sense if you drop, say, a Ping-Pong ball next to a golf ball. However, the reason the golf ball falls faster is that its greater density lets it overcome air resistance more effectively than the Ping-Pong ball can. If both were dropped in a vacuum, they would fall at the same speed. Astronomer and physicist Galileo Galilei is said to have proven this fact several centuries ago by dropping two heavy objects, one more massive than the other, from the Leaning Tower of Pisa in Italy. He let go of the objects at the same time, and they hit the ground at the same time. This upset people who believed that heavier objects fall faster than lighter ones. Galileo appeared to have shown that an ancient law of physics, which had become ingrained as an article of religious faith, was false. People had a word for folks of that sort: heretic. In those days, being branded as a heretic was like being accused of a felony.

With all the different systems of units in use throughout the world, the business of conversion from one system to another has become the subject matter for whole books. Web sites are devoted to this task; at the time of this writing, a good site could be found at Test and Measurement World. Click on the “Software” link, and then go to the page called “Calculator Programs.”