波幅前进,前进四

2s;解析:由(b)图可知,当纸带匀速前进20cm时,弹簧振子恰好完成一次全
1 惠更斯-菲涅尔原理ppt
bolt wins gold medal during men's 200m of athletics
bolt wins gold medal during men's 200m of athletics
三相波为负-正-负,第二相最显著,波幅高,时限0 抖音