So the Froude number is a measure of the ratio of inertial to gravitational forces.

因德数是惯性力与引力之比的量度。

He’s failing because he doesn’t know what kind of inertial force this object has to be able to grab it properly.

他失败了，因为他知道这个物体需什么样的惯性力才能正确抓住它。

Naturally a student knew nothing about mechanical laws, but he took for granted that he could learn, and went to his books to ask. He found that the force of inertia had troubled wiser men than he.

学生自然对力学定律一窍，他理所当然地认为他会学，就去他的书上请教。他发现惯性力困扰着比他更聪明的人。