This exploits the Doppler effect familiar when a siren changes pitch as the fire engine on which it is mounted speeds past you.
This exploits the Doppler effect familiar when a siren changes pitch as the fire engine on which it is mounted speeds past you.
这种方式利用的是多普勒效应原理——当消防车从你身旁一闪而过时，上面装着的警报器的音高就会发生改变，这点大家很熟悉。