Nothing is perfectly stiff. Nothing moves perfectly smoothly. Every mechanical part has some amount of "springiness" and will vibrate when struck, pushed, flexe

Nothing is perfectly stiff. Nothing moves perfectly smoothly. Every mechanical part has some amount of "springiness" and will vibrate when struck, pushed, flexed, etc. So a switch contact literally "bounces" like a hammer on a piano string as it is closed. His analogy of a ping-pong ball on a desk isn't great, but it's not exactly wrong, either. As for "immediate", the switch closure feels immediate to human perception (supposedly limited to about 1/20 second, for touch). But to modern electronics, nanoseconds are easily countable; and switch bounce can be measured in microseconds, or even milliseconds for a big, heavy electromechanical component. Here are some better articles. https://www.allaboutcircuits.com/technical-articles/switch-bounce-how-to-deal-with-it/ https://www.allaboutcircuits.com/technical-articles/switch-b... https://www.maximintegrated.com/en/design/technical-documents/app-notes/2/287.html https://www.maximintegrated.com/en/design/technical-document...