https://zh.toptenid.com/post/there-is-an-object-weighing-60-gw-resting-on-a-horizontal-table-apply-a-horizontal-pulling-force-of-30-gw-just-enough-to-pull-it-and-then-apply-a-force-of-20-gw-for-constant-velocity-motion-when-the-object-is-stationary-apply-a-force-of-20-gw