Camera shutter speed synchronized with helicopter blade frequencyWhen helicopter blades spin at an angle, they push air beneath them which creates lift. Sure, it's a simple way of looking at helicopters, but that's the basic premise.

What's amazing about this video is that the helicopter's rotor and blades hardly appear to be spinning at all and yet somehow it still manages to stay in the air. This is because the shutter speed on the camera (the amount of time the camera's sensor sees the image) has been set to the same speed that the blades rotate.