"We've now observed the instantaneous velocity of a Brownian particle," says Raizen. "In some sense, we're closing a door on this problem in physics.

Equipment: A tennis ball on a string. What it does: Swing the ball on the string to show circular motion. Release the ball to show the instantaneous velocity of the ball. Concepts Demonstrated: ...

Marc Lange, How Can Instantaneous Velocity Fulfill Its Causal Role?, The Philosophical Review, Vol. 114, No. 4 (Oct., 2005), pp. 433-468 ...

For frequencies ω < ω 0, on the other hand, the oscillations are closely approximated as the sum of parts proportional to the instantaneous velocity and acceleration of the oncoming stream; the phase ...