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Welcome to the Greenwood.Net Curiosity Corner
Can\'t Live Without It
Feb 08, 2010
Question: What causes gravity? (A condensation of several questions from Bob Skutt, Greenwood, S.C.)
Reply: One thing you can depend on is gravity. It causes things to fall, keeps planets in orbit and tries to halt an expanding universe, among other things. There are two theories explaining or describing gravity – classical and modern.
In classical physics, gravity is a fundamental force. “Fundamental” describes our ignorance. We don’t know what it is — only what it does. The classical interpretation is Newtonian physics. Isaac Newton (1642-1727) formulated a universal law of gravitation, an equation to calculate the force between two masses. (Universal because it is believed that it applies everywhere in the universe.)
Gravity is an attractive force between two objects (masses), just as the electrical force between unlike (opposite) charges is attractive. Two like charges experience a repulsive force, but gravity only attracts. Without Newton’s law and the description and understanding of how gravity acts, there would be no space program putting satellites in orbit or sending spaceships to the moon.
Let’s distinguish between mass and weight, which are commonly confused. Mass is a fundamental property that describes matter – the greater the mass of an object, the more matter it contains. The weight of an object is the downward gravitational attraction that the Earth exerts on an object – the more mass, the greater the weight. (If you are overweight, you are overmassed.) However, on the moon, where the gravitational attraction is 1/6 of that on the Earth (because the moon is less massive), the same object would weigh 1/6 as much, but the mass would be the same – something fundamental doesn’t change.
One other thing: The electrical force between charged particles can be shielded. That is, a barrier can be put between the particles and the force stopped. Gravity can’t be shielded — nothing stops it.
Einstein’s theory of general relativity (which is very complicated) brought forth a modern view of gravity. Here it is pictured as a gravitational field, something like space being an invisible fabric. Gravity is caused by a warping of space. For example, imagine the massive Earth on a rubber sheet of space. It would make a depression, and anything moving toward the Earth would fall into the depression – hence attractive gravity. If an object were moving near the Earth, it would follow around the depression, giving rise to a gravitationally curved orbit. That’s a quick explanation, but a detailed one would take a few weekly columns, and I have a feeling you would want to be curious about something else.
C.P.S. (Curious Postscript): I’m allergic to gravity. I turn it off before going to bed. ~JDW
Curious about something? Send your questions to Dr. Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC, 29649, or for e-mail, www.curiosity-corner.net. Selected questions will appear in the Curiosity Corner. © JDW
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