LOS ANGELES — Newly released video shows the moment a Google self-driving car learned the hard way not to tussle with a public bus. The collision happened on Valentine’s Day, when a Google vehicle struck the side of a public bus in the Silicon Valley city of Mountain View. Footage recorded by cameras on the bus shows a Lexus SUV, which Google has outfitted with sensors and cameras that let it drive itself, edging into the path of the bus that was rolling by at about 15 mph. It was the first time in several years of testing on public roads that a Google self-driving car prototype caused a crash.