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may have an effect on us, however small, as we pass them, as evidenced in
experiments that demonstrate the gravitational pull of mountains.
Gravitational forces are responsible for huge clouds of coalescing gases that
then ultimately implode, ignite, and become stars. It is gravity that keeps our
moon in orbit around the earth and the earth around the sun. It is gravity that
gives the galaxies their shape. Without gravity, much of the matter within the
universe would simply drift or fly off in all directions.
The Italian physicist and mathematician Galileo Galilei made experiments in the
latter part of the 16
th
century that established the effect of gravity on objects of
different weights, finding that they fell to earth at the same rate. Famously he
FIG 2.1
All objects fall at the same rate within a vacuum. Feathers fall slower only due to air resistance.
