Faster than light-speed camera.

By combining multiple high-speed exposures with very short laser pulses, MIT has figured out how to image waves of photons as they travel across a scene. Absolute genius. I actually met Doc Edgerton (referenced in the video) when I was a teenager. He would be impressed.

Slow-Motion Slinky

Sometimes physics contradicts our intuition. In slow motion the slinky appears to temporarily defy gravity. If you have ever tried to animate something springy, you'll know that getting it to look real takes a lot of forethought and some knowledge of how physics work.