Now, imagine a program where some of those objects are physically heavy and some are light: one is an anvil on a fuzzy rug and the other one is a ping-pong ball on a sheet of glass.
现在想像一个程序 里面的对象有重的有轻的. 一个铁砧在毛茸茸的地毯上, 另一个是一个乒乓球在玻璃上.