Vertical Motion Under Gravity Simulation

A ball thrown straight up slows down at 9.8 m/s² every second, stops for an instant at the top, and speeds up at the same rate coming down. With upwards taken as positive the acceleration is −g the whole time, including at the top. Without air resistance the flight is symmetric: it passes every height at the same speed on the way up and on the way down.

This vertical motion simulation throws a ball up from any height and plots height, velocity and acceleration against time, with strobe dots every quarter second to show the symmetry. In the two-ball mode you can drop one ball and throw another, from different heights and at different times, and find where they pass each other. Both feel the same g, so relative to each other they move at a constant velocity.