Simulations

Lift the load: the server picks a random load mass, pulley rig (including rope/pulley friction), goal direction (top or bottom), and a target time or speed (always achievable), you dial in the effort mass, and real Atwood-machine physics judges the attempt. Solving it refunds your run.

Swing a mass on a string in a horizontal circle at a chosen radius and constant speed — see the centripetal acceleration, force, and period, and watch the force grow with the square of speed.

Send two blocks toward each other on a frictionless track — adjust their masses, starting speeds, and coefficient of restitution to see momentum conservation and kinetic-energy loss in action.

Drop an object from a chosen height and watch gravity accelerate it — adjustable g, height, and mass (mass turns out not to matter).

Release a block from rest on a ramp — adjust the angle, friction, and ramp length to see whether it slides, and how fast it reaches the bottom.

Orbit two bodies about their barycenter — pick each body's mass (planets through stars) and the starting radius and speed to see circular, elliptical, and escaping (hyperbolic) trajectories; a body only glows like a star once it passes the fusion mass threshold.

Swing a pendulum from a chosen length and starting angle — numerically integrated, so large swings behave correctly (not just the small-angle approximation).

The server picks a random launch speed, gravity, bounciness, ground resistance, and a target landing zone plus a required bounce count (always achievable), you dial in the launch angle, and real projectile-motion physics judges the shot. Landing in the zone on exactly the asked bounce refunds your run.

Launch a projectile at a chosen speed and angle and watch it arc under gravity — see range, max height, and flight time; adjustable bounciness and ground resistance let it keep bouncing across the ground.

Pull a mass on a spring away from equilibrium and release it — adjust mass, spring stiffness, and damping to see undamped, underdamped, critically damped, and overdamped motion.

Release a sphere into a tall column of fluid — adjust its size, density, and the fluid's density and viscosity to see it asymptote to a terminal speed, or float, depending on which is denser.