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Explore equations, gravity, Euler's method, collisions, efficiency, and applications in this 3D physics simulation. Learn the concepts and strategies for accurate and optimized simulations.
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Steven Durant 3D Physics Simulation
Contents • Equations • Gravity • Euler’s Method • Simple Collisions • Correct Collisions • Efficiency • Applications • Screenshots
Gravity • F = G * M1 * M2 / R2 • Unavoidable efficiency of O(n2)
Euler’s Method • a = F / M • ∆v = a * ∆t • ∆p = v * ∆t
Simple (Elastic) Collisions • Check for collision via particle radius • Conservation of momentum • v1’ = v2 * M2 / M1 • v2’ = v1 * M1 / M2 • This method is flawed
Correct Collisions • Find next collision based on time • O(n2) • Find distance between particles • Find distance moved into each other ∆d ∆D
Correct Collisions • Find fraction of timestep until collision ∆t = 1 – ( ∆d / ∆D ) • Move both particles for the fraction • Use ∆t in Euler’s Equations • Calculate new velocities • Use conservation of momentum • Move both particles for the other fraction • Use (1-∆t) in Euler’s Equations
Efficiency • Pruning pairs of particles • Pairs moving away from each other. • Pairs too far apart. • Pretend their velocities are towards each other • If they still won’t collide before the nearest collision then their real velocities don’t need to be used or checked.
Application • Find out how long it would take for two apples on a frictionless table to collide by using realistic masses for the apples. • Put thousands of tiny little masses along a random distribution and see what the end product is. • Stuff orbiting each other? • One big blob?