1. The problem statement, all variables and given/known data I'd just like some verification really: see step three 2. Relevant equations net force = 0 --> equilibrium; net force = ma 3. The attempt at a solution I've come to the conclusion that the difference between newton's first law and second law is acceleration: Newton's first law: absence of acceleration Newton's second law: presence of acceleration I was wondering if it would be safe to say: "A particle not accelerating in an inertial frame of reference implies that the net force acting on the particle is zero" (after all, if it is not accelerating, wouldn't that automatically imply that the particle is a rest or moving at a constant velocity?) Instead of what the book more or less says: "A particle at rest or moving at a constant velocity in an inertial frame of reference implies that the sum of the forces acting on the particle is zero"