Universal Gravitation

Newton determined that the pull of Earth’s gravity caused both apples and

• the moon to fall toward Earth.

• the moon to move away from Earth.

• the sun to move away from Earth.

• stars to fall toward Earth.

The moon falls toward Earth in the sense that it falls

• with an acceleration of 10 m/s2, as apples fall on Earth.

• with an acceleration greater than 10 m/s2.

• beneath the straight-line path it would take without gravity.

• above the straight-line path it would take without gravity.

Planets remain in orbit while falling around the sun due to their

• tangential velocities.

• zero tangential velocities.

• accelerations of about 10 m/s2.

• centrifugal forces that keep them up. 

Newton did not discover gravity, for early humans discovered it whenever they fell. What Newton did discover is that gravity

• tells us about why the universe expands.

• tells us how to discover new planets.

• accounts for the existence of black holes.

• extends throughout the universe. 

Consider a space probe three times as far from Earth’s center. Compared at Earth’s surface, its gravitational attraction to Earth at this distance is about

• one third as much

• one half as much

• one ninth as much

• zero

Compared to the gravitational field of Earth at its surface, Earth’s gravitational field at a distance three times as far from Earth’s center is about

• one third as much

• one half as much

• one ninth as much

• .zero

Compared to the gravitational field of Earth at its surface, Earth’s gravitational field at Earth’s center is

• zero

• .half as much

• twice as much

• .three times as much

When an astronaut in orbit is weightless, he or she is

• beyond the pull of Earth’s gravity

• still in the pull of Earth’s gravity

• in the pull of interstellar gravity

• .beyond the pull of the sun’s gravity

The highest ocean tides occur when the Earth and moon are

• lined up with the sun

• at right angles to the sun

• at any angle to the sun

• lined up during spring

A black hole is

• simply a collapsed star

• a two-dimensional surface in space

• barely visible with high-powered telescopes

• a new form of gravity