
Other Situations
and Related Concepts
 Acceleration of gravity: Because
mass affects both the force of gravity and an object's resistance to accelerate (inertia),
all objects end up falling at the same rate.
 Gravity on Earth: On the Earth's surface, using its mass, we get
an acceleration of 9.8 m/s^{2}.
 Around other objects: The laws
of motion and gravity hold for any body around any gravitational
center of attraction, even asteroids, binary stars and galaxies...
By the way, gravity explains the fact that small moons
and asteroids are not round, while larger objects are.
 Satellites around the Earth:
Larger orbits have longer periods; e.g., geosynchronous ones
[42,000 km], or 90 minutes for the Space Shuttle.
 Our Moon: Its orbit is elliptical too (and the period that enters into Kepler's laws is the sidereal
month, rather than the lunar/synodic one!).
 New concept: The escape velocity
from a center of attraction; depends on its mass and size [11 km/s from
the Earth's surface].
