Why do propellers look like they are not moving?

Propellers can appear to be not moving due to the phenomenon known as the "stroboscopic effect," which occurs when the rotation speed of the propeller coincides with the frame rate of a camera or the flicker of artificial lights. This optical illusion causes the blades to seem stationary or even to rotate backward. Additionally, the high speed of propeller blades and their design can also contribute to this effect, making them blend into the background and appear less visible during rapid motion.