Tuesday, February 12, 2013

Attractive Forces of Nature Part I: Gravity

It's that time of year again when you and your sweetheart wish to exchange saccharine expressions of your love for one another. Love is a many-splendored incomprehensible thing, so we tend to turn to the "incomprehensible" forces of nature to aid in our descriptions. "I love you like the ocean loves the beach." The ocean touches the beach, but is it really attracted to it? How strong is your love? Is it strong like the gravity that keeps us from floating into space, or is it even stronger than that? We hope this special series: Attractive Forces of Nature will help you express your love and impress your sweetheart this Valentine's day.

We'll begin with gravity. Love can often catch us unawares like an apple to the head, as goes the story of Newton's discovery of gravity. In reality, although Newton said that the falling of an apple inspired his work, the law of gravitation did not come to him instantaneously but after a great deal of thought and work. In fact, even before Newton came along, Galileo had conjectured that all objects are pulled toward the center of the earth with the same acceleration. Newton further fleshed out the law of universal gravitation, which acts on every object on and off the earth.

The force of gravitational attraction between two objects is expressed by:

Where G is the universal gravitational constant, m1 and m2 are the masses of the objects, and r is the distance between the center of mass of the two objects. This force causes the earth and other planets to stay in orbit around the sun. It would cause two objects in solitary space to orbit each other (you and your love in space suits, for example).

You and your sweetheart...  in space.
On Earth, however, it's a different story.  Although you and your love may be able to get closer to each other than either of you could get to the center of the earth, the earth is so much more massive than you that, at least from a gravitational standpoint, both you and your sweetheart are significantly more attracted to the center of the earth than you are to each other.  So you should probably avoid bringing it up, especially on Valentine's day.

Stay tuned. We'll be publishing articles on the other forces from now until Valentine's day!