/* The following is not free software. You may use it for educational purposes, but you may not redistribute or use it commercially. (C) Burak Kanber 2012 */ var canvas = document.getElementById('canvas'), ctx = canvas.getContext('2d'), height = 400, width = 400, x = 200, y = 0, vy = 0, ay = 0, m = 0.1, // Ball mass in kg r = 10, // Ball radius in cm, or pixels. dt = 0.02, // Time step. e = -0.5, // Coefficient of restitution ("bounciness") rho = 1.2, // Density of air. Try 1000 for water. C_d = 0.47, // Coeffecient of drag for a ball A = Math.PI * r * r / 10000 // Frontal area of the ball; divided by 10000 to compensate for the 1px = 1cm relation ; ctx.fillStyle = 'red'; function loop() { var fy = 0; /* Weight force, which only affects the y-direction (because that's the direction gravity points). */ fy += m * 9.81; /* Air resistance force; this would affect both x- and y-directions, but we're only looking at the y-axis in this example. */ fy += -1 * 0.5 * rho * C_d * A * vy * vy; /* Verlet integration for the y-direction */ dy = vy * dt + (0.5 * ay * dt * dt); /* The following line is because the math assumes meters but we're assuming 1 cm per pixel, so we need to scale the results */ y += dy * 100; new_ay = fy / m; avg_ay = 0.5 * (new_ay + ay); vy += avg_ay * dt; /* Let's do very simple collision detection */ if (y + r > height && vy > 0) { /* This is a simplification of impulse-momentum collision response. e should be a negative number, which will change the velocity's direction. */ vy *= e; /* Move the ball back a little bit so it's not still "stuck" in the wall. */ y = height - r; } draw(); } function draw() { ctx.clearRect(0, 0, width, height); ctx.beginPath(); ctx.arc(x, y, r, 0, Math.PI * 2, true); ctx.fill(); ctx.closePath(); } /* A real project should use requestAnimationFrame, and you should time the frame rate and pass a variable "dt" to your physics function. This is just a simple brute force method of getting it done. */ setInterval(loop, dt * 1000);

<canvas id="canvas" height="400" width="400"></canvas>

canvas { display:block; margin:10px auto; border:1px solid #999; }