Newton didn't express his second law of motion in a single, concise sentence. His original work, "Philosophiæ Naturalis Principia Mathematica," was written in Latin, and he described the law using a more detailed, mathematical approach. Here's a translation of the relevant passage from the *Principia*:

> "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."

Let's break it down:

* "The alteration of motion...": This refers to the change in an object's velocity (either in speed or direction).

* "...is ever proportional to the motive force impressed...": This means that the change in velocity is directly proportional to the force applied to the object. A larger force results in a larger change in velocity.

* "...and is made in the direction of the right line in which that force is impressed.": This means that the change in velocity occurs in the same direction as the force applied.

While not a single sentence, this clearly expresses the fundamental principle of Newton's second law of motion: Force causes acceleration, and the acceleration is directly proportional to the force and inversely proportional to the mass.

It's important to note that this is a simplified explanation. Newton's *Principia* used more rigorous mathematical language to express these ideas. Modern physics often represents the second law as the equation F = ma, where F is force, m is mass, and a is acceleration.