It's remarkably easy to get light to smear--that's the wonder of non-instantaneous exposures. The easiest way I've found to do it is wait for the late evening, when the sky is a deep, dark blue but it's not quite night, and take a photo of something moving at any speed, really. I like the almost otherworldly effect that is created by it, where the world is frozen but the subject of the photo is moving too fast to be anything but a blur.
Subjects like this Type 4 MAX train I caught one evening in Portland, pulling away from Skidmore Fountain and heading toward the airport. It makes it look like the train's moving a lot faster than it really is; that's just one of the ways the camera lies.
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