Gravitation is the universal force of attraction between
two bodies. It depends on two principal factors: mass
and distance. The greater the mass, the greater will be the
attraction; on the other hand, with greater distance, the force
of gravity is less. A spacecraft in orbit is essentially constantly
falling around the Earth, and astronauts aboard do not feel the
force of gravity even though they are being pulled by the
Earth's gravity. This condition of seeming weightlessness is
called a microgravity environment.