Page 22 - 443

Gravity

In 1687, English scientist Isaak Newton published his
theory of universal gravitation. He said that all objects in the
universe are attracted to each other by the force of gravity. The
sun’s gravity attracts the planets and other bodies in the solar
system and prevents them from flying off into space.
The strength of the force of gravity between any two
objects depends on two factors: the mass of the two objects and the
distance between them. The heavier the objects are, the stronger
the gravitational force between them. The greater the distance
between them, the weaker this gravitational force.
If two objects are very massive, as in the case of the sun
and the earth, then the gravitational force between them will be
strong, even when they’re far apart. That’s why the earth is held in
its orbit by the gravitational pull of the sun - even though the sun is
93 million miles away.
Tides, the regular rise and fall of waters in oceans and seas,
are caused by the pull of the moon’s gravity on the earth. So as the
moon moves in relation to the earth, the waters of the earth move,
too. Tides rise and fall twice every lunar day, or every twenty-four
hours and fifty-one minutes. As the earth turns, the part of the
oceans facing the moon will be at high tide.

Comprehension Questions
I. Say which of the following statements are false and
which are true. Correct the false statements to make them
true.
1. In 1687 he published his theory of universal gravitation.
2. The Sun’s gravity prevents in the solar system from flying
off into space.
3. The strength of the gravity force between any two objects
does not depend on the distance between them.
4. The heavier the objects are, the stronger the gravitational
force between them.
5. Tides are not caused by the pull of the Moon’s gravity on
the Earth.

20