This simulator drives a sliding test carriage across a rough horizontal bed using an ideal bidirectional actuator, with adjustable mass, applied force, static and kinetic friction coefficients and initial velocity. It separates every horizontal force acting on the carriage — applied force, friction and the actuator's own reaction — so each of Newton's three laws can be observed on its own.
• A real-time 3D rough test bed with replaceable friction pads, a carriage with adjustable mass plates, a servo actuator and force transducer, orange/violet/teal/blue free-body force arrows for applied force, friction, normal force and weight, and a reaction indicator on the actuator itself — with home view, focus-selected-part, auto-rotate, expand and toggleable labels. • Five live controls: carriage mass (1–10 kg), applied horizontal force (−30 to 30 N, right positive), static friction coefficient (0–0.8), kinetic/static friction ratio (0–1, giving μk = ratio × μs) and initial velocity (−2 to 2 m/s). • Nine live metrics: position, velocity, acceleration, net horizontal force, friction on the carriage, normal force, static friction limit, kinetic friction coefficient and kinetic energy. • A Curves & measurements tab charting force balance and velocity history, the full model equations and snapshot measurements. • An Experiments tab with four guided scenarios (static balance, breakaway, inertial motion, friction stopping test), a model-verification bench of independent automated checks, and a timestamped event log with a copyable trial report. • A Learn & assess tab with guided lessons, a two-question knowledge-check quiz and a written scope/reference statement.
Below the breakaway threshold, static friction is not a fixed value — it adjusts itself to exactly balance the applied force, up to its limit of μsN, keeping the carriage motionless (Newton's first law in action). Once applied force exceeds that limit, friction drops to its constant kinetic value μkN opposing velocity, and acceleration follows directly from summing forces: a = (F + f)/m. The static-balance experiment applies 5 N to a 2 kg carriage and shows static friction responding with exactly −5 N, holding position and velocity at zero; the breakaway experiment raises that to 12 N and shows kinetic friction settling at −5.886 N with resulting acceleration of +3.057 m/s².
The actuator pushes the carriage forward with some force, and by Newton's third law the carriage pushes back on the actuator with an equal and opposite force — but that reaction acts on the actuator, not on the carriage, so it must never be added into the carriage's own force balance. The reaction indicator makes this explicit by displaying the actuator's reaction as a separate quantity from the carriage's own net force. The friction-stopping-test experiment demonstrates a related idea: give the carriage 2 m/s with force removed, and kinetic friction alone brings it to rest in about 0.680 s over about 0.680 m, then holds it there with static friction at zero net force.
No — that product is only the limiting maximum magnitude static friction can reach. Below breakaway, static friction takes on whatever value is needed to balance the applied force and keep the carriage at rest, as shown in the static-balance experiment where 5 N of applied force is met by exactly −5 N of static friction.
On the actuator itself, not on the carriage. Newton’s third-law force pairs always act on two different bodies: the actuator pushes the carriage forward, and the carriage pushes back on the actuator with equal and opposite force — that reaction must never be summed into the carriage’s own net force.
It continues moving at constant velocity indefinitely, with zero acceleration — a direct demonstration of Newton’s first law. The inertial-motion experiment sets force and friction to zero and confirms velocity stays fixed at its initial value.
It is a one-dimensional Coulomb-friction model on a level rigid bed using g = 9.81 m/s², with an ideal force actuator and no compliance, rolling resistance or aerodynamic drag. Kinetic friction is capped so it never exceeds the static limit, the display ends at ±5 m without modeling an impact, and editing any parameter starts a fresh trial.