Newton's First Law of Motion: When ΣF = 0

The Constant Velocity Lab — Newton's First Law of Motion

Newton's first law of motion states that, in an inertial reference frame, a body's velocity cannot change unless a nonzero net external force acts on it. This simulation lets AP Physics 1 students see the law in action on a moving car. Use the sliders to adjust the forward static friction from the road, the backward drag and rolling resistance, and the car's mass. Watch the net force ΣF, the acceleration a = ΣF/m, and the velocity v update in real time, alongside a live v-vs-t graph. When ΣF = 0 the velocity holds constant — including the special case v = 0. Nudge either force and the velocity immediately begins to change. The simulation isolates the biconditional "constant v ⇔ ΣF = 0" and confirms why a car's engine never appears on its free body diagram.