【導(dǎo)讀】解析波源(即振源)振動(dòng)時(shí),依靠介質(zhì)中的相互作用力帶動(dòng)周圍各部分質(zhì)點(diǎn)振動(dòng)起來(lái),為波源,設(shè)波源的振動(dòng)周期為T,自波源通過(guò)平衡位置豎直向下振動(dòng)開(kāi)始計(jì)時(shí),經(jīng)過(guò)T4,質(zhì)點(diǎn),7、8質(zhì)點(diǎn)間的振動(dòng)步調(diào)相差T4,故選項(xiàng)C正確;質(zhì)點(diǎn)9與質(zhì)點(diǎn)1相距2個(gè)波長(zhǎng),質(zhì)點(diǎn)9比質(zhì)點(diǎn)1晚2T開(kāi)始起振,一旦質(zhì)點(diǎn)9起振后,質(zhì)點(diǎn)1、9振動(dòng)步調(diào)就完全一致,確;由機(jī)械波的傳播特點(diǎn)可知,選項(xiàng)C正確;波只有在同種均勻介質(zhì)中才會(huì)勻速傳播,一質(zhì)點(diǎn)總是落后,故B、C正確;形成機(jī)械波的各個(gè)質(zhì)點(diǎn)只是在平衡位置附近往復(fù)運(yùn)動(dòng),