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 Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place...The Space and Astronomy Agora Straight Lines Refuse To Be Discriminated Against Forum List | Follow Ups | Post Message | Back to Thread TopicsPosted by Brian Kirk Parquette on September 28, 2001 19:53:18 UTC

The Evolution of Physics by Albert Einstein and Leopold Infeld copyright 1938 page 11- 12
“If a stone is dropped from the top of a tower its motion is by no means uniform; the velocity increases as the stone falls. We conclude: an external force is acting in the direction of the motion. Or, in other words: the earth attracts the stone. Let us take another example. What happens when a stone is thrown straight upward? The velocity decreases until the stone reaches its highest point and begins to fall. This decrease in velocity is caused by the same force as the acceleration of a falling body. In one case the force acts in the direction of the motion, in the other case in the opposite direction. The force is the same, but causes acceleration or deceleration according to whether the stone is dropped or thrown upward.”
“All motions we have been considering are rectilinear, that is, along a straight line. Now we must go one step further. We gain an understanding of the laws of nature by analyzing the simplest cases and by leaving out of our first attempts all intricate complications. A straight line is simpler than a curve. It is however, impossible to be satisfied with an understanding of rectilinear motion alone.”