She sat in the car and revved the engine while she waited for us.她坐在车里并在等待我们的同时调高了发动机转速。The speed of rotation gradually decreases to zero.转速渐渐降至零。The engine delivers instant acceleration whatever the revs.不论转速如何,发动机都可以立即加速。The machine slowed down and stopped.机器转速逐渐减慢,并终于停住了。