Forces & motion
Choose a setup, predict the motion, then play.
Why? Look inside the model
The force balance
N is the normal force; W is weight; f is signed friction. Positive directions are shown above.
The colored arrows are real forces. mg sin θ and mg cos θ are components of weight, not extra forces.
Model assumptions
Rigid bodies; g = 9.81 m/s²; no air drag. Connected systems use one taut, massless rope and a frictionless, massless pulley. Fixed-pulley masses have the same speed and equal rope tension. For a movable pulley, the free end moves twice as far as the load. μk ≤ μs. Travel ends at ±1 m; the experiment stops before modeling impact.
Static friction adjusts up to μsN. Once sliding, kinetic friction has magnitude μkN and opposes velocity. Every new setting starts from rest.
OpenStax: Newton’s laws / Friction