How short is an "instant"? Is it a second? A tenth of a second? A microsecond? You might think all of these qualify. What about 100 years? That certainly doesn't seem like an instant, and to a human ...

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: ...

An instantaneous stop would subject everything not anchored to the planet to a sudden deceleration. At the equator, this means an abrupt halt from a speed of about 1,600 km/h.