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 form that
force (F) is equal to the mass (m) times the acceleration (a) :
F = m * a
Since acceleration is
a change in velocity (V) with a change in time (t), we can also write this equation
in the difference form shown on the slide.
F = m * (V1 - V0) / (t1 - t0)
The important fact is that a force
causes a change in velocity; and likewise, a change in velocity generates
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 the
and the aircraft
weight and thrust
can be computed by using the second law of motion.
- Re-Living the Wright Way
- Beginner's Guide to Aeronautics
- NASA Home Page