Universal Law of Gravitation
What Really Happened with the Apple?
Probably the more correct version of the story is that Newton, upon observing
an apple fall from a tree, began to think along the following lines:
The apple is accelerated, since its velocity
changes from zero as it is hanging on the tree and moves toward the ground.
Thus, by Newton's 2nd Law there must be a force that acts on the apple to cause
this acceleration. Let's
call this force "gravity", and the associated acceleration the "accleration due
to gravity".
Then imagine the apple tree is twice as high. Again,
we expect the apple to be accelerated toward the ground, so this suggests that
this force that we call gravity reaches to the top of the tallest
apple tree.
There is a popular story that Newton was sitting under an apple tree, an apple
fell on his head, and he suddenly thought of the Universal Law of Gravitation.
As in all such legends, this is almost certainly not true in its details,
but the story
contains elements of what actually happened.
