EPISODE PREVIEW
In the evolution of physics, the contributions of Newton and Einstein occupy center stage. This film explores the revolution that ensued when Einstein's theory of relativity upset Newton's elegant description of the universe.
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Here are two equations that have something in common. Don't worry, I'll put them into words.
The Force of Gravity
In words rather than symbols, this equation says that the gravitational force (F) that two objects with masses m1 and m2 exert upon each other depends on the distance (r) between them. G is a number that must be measured, called a constant, which has been measured in many instances and always comes out the same. It makes the two sides of this equation balance. (It is called Newton's gravitational constant.)
The Brightness of Stars
In words rather than symbols, this equation says that the flux (F, the light received from a light source such as a star) depends on on the distance (r) between them, and on the inherent brightness (L) of the light source, which is called its luminosity. The constant π is the familiar 3.14... , the ratio of a circle's perimeter to its diameter.
The main thing these equations have in common is that little r in the numerator of both equations.
Using the first equation, can you answer these questions?
1) If one of the objects moves farther away from the other (the distance r increases), does the force of gravity (F) between them increase or decrease?
2) Is the force simply proportional to the distance; that is, does doubling the distance make the force increase or decrease by a factor of 2, or by some other factor?
Using the second equation, same questions:
1) If a star moves twice as far from Earth (r increases twofold), does its apparent brightness (F) increase or decrease?
2) Is the increase or decrease twofold, or some other amount?
Finally, is the numerator of the second equation familiar to you? If so, where have you seen it before? What's it doing here?
© 1974, British Broadcasting Company
