tailieunhanh - The Craft of Scientific Presentations - M Alley (Springer 2003) Episode 9

Tham khảo tài liệu 'the craft of scientific presentations - m alley (springer 2003) episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 154 The Craft of Scientific Presentations began by saying that he was to perform an experiment that would place himself in physical danger. Although he said that he could be seriously injured in the experiment he claimed that he had not practiced it because he was so confident that the laws of physics would keep him safe. So after preliminary discussion about a pendulum s trajectory its period and its minimum and maximum speeds the new professor pulled the medicine ball to one wall of the room and climbed on top of a stepladder. With his back against the wall the professor held the medicine ball to his chin and said that he was going to release the ball with zero velocity and that when it returned to this position by the laws of physics the velocity would again be zero. Well this new professor s goal had been to engage the students and as he stood on top of that ladder with the huge ball against his chin he certainly had them engaged. When the professor let the ball go it swung through its arc attaining a maximum velocity at the low point of the arc and rising almost to touch the far wall. Then the ball started its return trajectory. Apparently because the new professor had not practiced this demonstration he was unprepared for the sight of the huge ball making its way back toward him. According to students in the room although his eyes grew large he refused to bail out. Instead he braced himself but in so doing he must have leaned forward ever so slightly. What the new assistant professor ended up demonstrating was not so much the motion of a pendulum but the conservation of momentum because the students saw that a large mass the medicine ball with little velocity struck a small mass the new assistant professor s head and imparted to it a relatively fast velocity. The new assistant professor s head snapped back and hit the wall and he fell unconscious to the floor. Visual Aids Your Supporting Cast 155 For a moment no one in the class moved. Then a few students .