Every body continues in its state of rest, or of uniform motion in a right straight line, unless it is compelled to change that state by forces impressed upon it. Isaac Newton
Every body continues in its state of rest or uniform motion in a straight line, except insofar as it doesn't. Arthur Eddington
The natural law of inertia Matter will remain at rest or continue in uniform motion in the same straight line unless acted upon by some external force. W. Clement Stone
We do not have and cannot have any means of discovering whether or not we are carried along in a uniform motion of translation. Henri Poincaré