Yes, if the same amount of force is applied to two objects, then the
lighter one will accelerate faster, according to Newton's Second Law,
F=ma. Here, F is the sum of all forces on the object. For an airplane,
there are four forces involved:
- weight -- gravity pulls down.
- lift -- airflow past the wings generates an upward force.
- drag -- airflow past the airplane pushes back on the airplane and slows it down
- thrust -- jet or propellor engines push the airplane forwards
Typically, airplanes which fly long distances, like commercial
passenger aircraft, do so at more or less constant speeds over most of
the journey. So the acceleration is zero most of the time! Fuel must
still be burned to overcome drag and to redirect airflow to generate
lift. How far an airplane (with an engine) flies depends on how much
fuel it can carry, and how heavy it is (and on things like its wing
design). A heavy airplane must constantly expend energy pushing through
the air, directing airflow downwards to push itself up so it doesn't
If the airplane doesn't have an engine (such as a paper airplane),
then it will travel farther and stay aloft longer if it starts out
faster. But a very light paper airplane has a problem with drag -- if
the airplane is very light, it doesn't take much of a drag force to
slow it down.
(republished on 07/12/06)