Difference between stiffness and weakness is the existence or nonexistence of the system.

To play, press and hold the enter key. To stop, release the enter key.

press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom
press to zoom

단단함과 약함의 차이는 구조(system)의 유무이다.