Everything moves, even if it doesn't
seem to be moving, because motion is relative. For example, a book
that is at rest, relative to a table, is actaully moving at about 30 km/s
relative to the sun.
Speed is a measure fo how fast something
is moving. It is defined as distance covered divided by time.
Speed at any instant is defined as instantaneous speed. Average speed is defined as
average speed = total distance covered
time interval
Velocity and speed are different. Velocity is speed in a certain direction.
Acceleration is the rate at which the velocity is changing. The formula for acceleration is
acceleration = change of velocity
time interval
Free fall is motion under the influence of a gravitational force. Objects fall at 9.8 a/s or 32 ft/s2 when there is no air resistance. Air resistance effects free fall. If you drop a coin and a feather, the coin will hit the ground first because air resistance causes the feather to fall more slowly. If you drop the same coin and feather in vaccum environment, the they will hit the ground at the same time.