Gravity is the force of attraction that pulls
things together. On Earth, we experience it as
the force that pulls us down onto the surface
of the planet. In the universe, gravity is the
force that pulls planets in orbit around stars.
Weight and mass
Weighing scales measure
the pulling force that
Earth’s gravity exerts on
your body. Gravity exerts
more pulling force on a
body with greater mass, so
the scales would register a
higher weight for a person
with greater mass.Gravity
TERMINAL
VELOCITY The highest
velocity reached by skydivers
with an unopened parachute is
about 125 mph (200 km/h).
Opening a parachute slows the
skydiver down by increasing drag.Gravity
and Galileo
The first scientist to
study gravity seriously was an Italian
named Galileo Galilei (1564–1642). He
did lots of experiments and concluded that
in the absence of air resistance all falling
objects would accelerate downward at the
same rate. It is the air resistance, called
drag, that allows some objects to reach the
ground more slowly than others.GRAVITY AT WORK
Take up skydiving and you will soon feel the full
effects of gravity at work. When you jump out of a
plane, gravity makes your body accelerate toward the
ground. At the same time, air rubs against your body,
creating friction, or drag, which works against gravity.
Eventually the two forces balance, and you stop
accelerating—you have reached “terminal velocity.”WEAK OR STRONG?
Gravity may seem impressive, but it is
actually the weakest known force in the
universe. It takes objects the size of planets
and stars to produce a noticeable effect.
The Sun’s gravity is strong enough to hold
all the planets of the
solar system in
orbit around it. According to legend,
Galileo dropped balls
of different weights
from the Leaning Tower
of Pisa to show they hit
the ground at the
same time.SCIENCE