How can you have a shutter speed that's slower than your FPS?

Think of it from a mechanical perspective: an exposure is the amount of time a shutter is open. When you're shooting movies you're usually at 24fps. That number is a hard lock; you can't go slower because it's not about the individual frame, it's about the stream of 24fps. If you were to make an exposure any slower than 1/24 of a second (the standard is 1/48, or a 180deg shutter) there would be physical smear as the shutter opens and shuts at a slower rate than the hard-locked 24fps stream.

You could definitely try and crank it down to 1/12 or 1/6 but the frames would bleed into another. In a strip of film, the whole thing is sensitive, the frames are established at exposure. With movies, the film moves through at a preset speed to guarantee a certain amount of frames per foot of film. That's why we measure in shutter angles instead of fractions! Everything is assumed to be based off of 24fps. Or whatever your 'time base' is, be it 60fps or 120fps or whichever. Using fractions for moving images is something that became more widespread after DSLRs and it's not really accurate because it's an entirely different concept missing the motion aspect entirely.

If your exposure is half of your framerate, that means you're not going to have that flicker between the two frames to make them distinct; when you halve it, you interrupt the optical illusion that makes movies work!

We're all constrained by physics! A solution for you would be to get several cameras to multiply you back to your time base. So if you want a 1/12 look, with the motion blur, you'd need to take two cameras out, stagger their exposure by 1/12 of a second, then take each frame and inter-splice them into a 24fps stream, and you'd get moving pictures again.

I hope your reflexes are on point!

/r/videography Thread