Can D90 do slow motion video?

No, the end of this video has been written. Phantom Flex high-speed camera is used to shoot 1080P HD video with a frame rate of 2570fps. When the video frame rate is high enough (that is, shooting more than 2,000 images per second), playing back at the normal rate (24fps) will produce a slow-motion effect, while the current video shooting SLR can reach 60fps at most (the cost of this camera is not as high as 50,000 or even hundreds of thousands of dollars)

You can try to shoot a still image similar to a water drop with a high-speed shutter, which is not a problem for an entry-level SLR with the highest shutter speed of 1/4000 seconds, but it is not practical to shoot a slow-motion movie.