Newton's laws of motion
Isaac Newton, Philosophiae naturalis principia mathematica
Translated by Andrew Motte (1729)
Corpus omne perseverare in statu suo quiescendi vel movendi
uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum
Every body perseveres in its state of rest, or of uniform motion in a right
line, unless it is compelled to change that state by forces impressed thereon.
Projectiles persevere in their motions, so far as they are not retarded by the
resistance of the air, or impelled downwards by the force of gravity. A top,
whose parts by their cohesion are perpetually drawn aside from rectilinear
motions, does not cease its rotation, otherwise than as it is retarded by the
air. The greater bodies of the planets and comets, meeting with less resistance
in more free spaces, preserve their motions both progressive and circular for a
much longer time.
Mutationem motus proportionalem esse vi motrici impressae, &
fieri secundum lineam rectam qua vis illa imprimitur.
The alteration of motion is ever proportional to the motive force impressed; and
is made in the direction of the right line in which that force is impressed.
If any force generates a motion, a double force will generate double the motion,
a triple force triple the motion, whether that force be impressed altogether and
at once, or gradually and successively. And this motion (being always directed
the same way with the generating force), if the body moved before, is added to
or subtracted from the former motion, according as they directly conspire with
or are directly contrary to each other; or obliquely joined, when they are
oblique, so as to produce a new motion compounded from the determination of
Actioni contrariam semper & aequalem esse reactionent: sive
corporum duorum actiones in se mutuo semper esse aequales & in partes
To every action there is always opposed an equal reaction; or the mutual actions
of two bodies upon each other are always equal, and directed to contrary parts.
Whatever draws or presses another is as much drawn or pressed by that other. If
you press a stone with your finger, the finger is also pressed by the stone. If
a horse draws a stone tied to a rope, the horse (if I may so say) will be
equally drawn back towards the stone: for the distended rope, by the same
endeavour to relax or unbend itself, will draw the horse as much towards the
stone as it does the stone towards the horse, and will obstruct the progress of
the one as much as it advances that of the other.