It is caused by the Doppler effect (something similar happens when a police car or fire engine with its siren blaring drives past you, and the pitch of the sound suddenly drops).

这是由多普勒效应(类似一辆警车或消防车鸣着警笛从你身边经过，之后音高突然下降)引起的。

youdao

For 20 minutes, the Sharmas listened to a sales pitch from staff selling the Reva, a small but peppy electric car that retails for $6,000.

在那里,销售人员向Sharmas一家推荐Reva,一款小巧而擅长高速的电动车.这辆车的售价是6,000加元.

youdao

The product has strong decontamination, it quickly removes pitch, grease, dirt form car finish and wheel. It also clean and gloss over the surface.

本产品具有特强去污能力，能迅速清除汽车、摩托车、合金框其表面的柏油及油渍污垢，并同时具上光效果，能令阁下座驾洁净光亮。

youdao

This is a reddening of a galaxy's spectrum caused by the Doppler effect (the effect that causes a police-car siren to drop in pitch as the car drives away).

ECONOMIST: Astronomy

He begins a sales pitch the way most car salesmen do, with friendly chitchat.

FORBES: Virtual Test Drive

As well as the club's main football pitch, there will also be an artificial pitch, education centre and car park.

BBC: Suffolk FA to invest in Bury Town's community facilities