The wagon-wheel effect (alternatively, stagecoach-wheel effect, stroboscopic effect) is an optical illusion in which a spoked wheel appears to rotate differently from its true rotation. The wheel can appear to rotate more slowly than the true rotation, it can appear stationary, or it can appear to rotate in the opposite direction from the true rotation. This last form of the effect is sometimes called the reverse rotation effect.
Here is a video that demonstrate the wagon wheel effect on helicopter choppers:
In the following video you can find more about the wagon wheel effect. In the video you can see a wheel that seems stationary. The video explains the connection between the wagon wheel effect and the camera's recording rate.
In this video you can find a detailed explanation about the effect. Watch the video and answer the question.
What makes us see a filmed spinning wheel as it spinning backward or being stationary?