英语时差：科学物理测验（下）

Once the ball leaves the tube it will move in a perfectly straight line. What’s interesting, though, is that it wasn’t until the 17th century that this was realized to be the case. For hundreds of years people thought that some aspect of the thing that moved an object stayed in the object. That sounds a little weird, but if you thought the ball would continue in a curved path, you were subscribing to this theory. Curved tube, curved motion. Newton’s laws of motion stated that an object will always move in a straight line unless it is prevented from doing so. The curved tube prevents the ball from moving straight only as long as the ball is inside. Once free, however, it moves straight once again. And it will continue to do so as long as nothing interrupts this motion.