Math isn't all nerdery and monotonous tedium with the abstract; it explains real phenomenon and cool effects, such as this seemingly magic helicopter.
Of course, the helicopter shown in the video above isn't actually magically flying without its rotors turning. What's happening is a consequence of shutter speed and frame rate. First, the shutter speed is fast enough to effectively eliminate any motion blur. Second (and the basis of the effect), the rotor RPM is some integer multiple of one-fifth of the frame rate of the camera. What this means is that the blades are rotating at a speed that precisely matches the frame rate and places them effectively in the same position every frame, making it look as if they haven't moved at all. Why "effectively" and why the factor of one-fifth? Because there are five identical blades, meaning that the blades don't have to return to identical positions between frames, only that they have to rotate at a speed such that the set occupies the same overall position in space; it might be that the second blade moves into the fifth blade's slot between frames and so on, but our eyes can't distinguish them, and thus, the helicopter appears to be flying with its engine magically turned off. It's a neat illustration of movement synchronizing with video frame rate.
[via PetaPixel]
This is so clever! haha
Someone accidentally hit the thumbs down. This is cool
They must still have post-calculus nightmares. ;)
Cool stuff. Care to share the frame rate so we can try at home?