The laws of physics should be tested in a variety of ways. Based on the problem that instantaneous velocity cannot be obtained directly when verifying the conservation law of mechanical energy in PEP textbooks and other experimental designs, this paper proposes an alternative experimental design to "visualize" the instantaneous velocity, by using the knowledge of circular motion that students are familiar with, and the real-time data processing function of DIS. Meanwhile, students can also intuitively realize the existence of resistance in the experiment process through the experiment, and will get a deep understanding of the conditions under which the law of conservation of mechanical energy is established.