Force:
Sir Isaac Newton first presented his
three laws
of motion in the "Principia Mathematica Philosophiae Naturalis"
in 1686. His second law defines a force to be equal to the
differential change in momentum per unit time as described by the
calculus of mathematics which Newton also developed. The momentum is
defined to be the mass of an object times its velocity. If the mass is a
constant, the second law reduces to the more familiar product of a mass
and an acceleration (F = ma). Since acceleration is a
change in velocity with a change in time, we can also write this
equation in the third form shown on the slide. The important fact is
that a force will cause a change in velocity; and likewise, a change in
velocity will generate a force. The equation works both ways. The
velocity, force, acceleration, and momentum have both a magnitude
and a direction associated with them. Scientists and mathematicians call
this a vector quantity (magnitude plus direction.) The equations
shown here are actually vector equations and can be applied in each of
the component directions.
The
motion
of an aircraft resulting from aerodynamic
forces and the aircraft weight
and thrust
can be computed by using the second law of motion.
Differential
Form: Force = change of momentum with change of time F
= d(mv) / dt
With Mass
Constant: Force = mass x acceleration F
= m x a
or
Force = mass x change in velocity with time
F = m(V1V0) 
