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.

Release a cart from rest on a curved track and watch its energy change hands. Going down, stored (potential) energy becomes motion (kinetic) energy, and climbing again stores it back. Live bars show the kinetic, potential and heat energy in joules, and the total never changes. Add friction to see energy turn into heat, so each swing is lower than the last until the cart stops. Change the track, height, mass and gravity, and start high enough on the hilly track to roll right over the hill and off the end.

The server picks a track, cart mass, gravity and friction, plus a target zone for how far the cart rolls in total before it stops (always achievable), you dial in the release height, and real energy-on-a-track physics judges the run. Stopping in the zone refunds your run.

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 world (the Moon, Mars, Earth or Jupiter), a release angle and a target for how long one full swing should take (always achievable), you set the length of the string, and a real pendulum model judges whether one swing takes that long. Hitting the beat refunds your run.

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.

The server picks a thick liquid (such as glycerine or castor oil), a ball material (such as steel or glass) and a target for the steady sinking speed (always achievable), you choose the ball's radius, and a real terminal-velocity model judges how fast it settles. Hitting the target refunds your run.

Hang a mass at a chosen distance from the pivot on each side of a beam, add weight to the beam itself, and shift the pivot off centre — watch the beam swing down on the heavier side and settle, or stay level when the two torques exactly match.