You are videotaping the car in the photo below at a rate of

You are videotaping the car in the photo below at a rate of 30 frames per second (fps), a) At what rotation rate (in RPM) will the wheel appear rotating backwards in the video? b) At what rotation rate will the wheel appear stopped in the video?

Solution

1 fps = 60 RPM

30 fps = 1800 RPM

a) When the rotation rate becomes greater than 1800 RPM, the wheel would appear rotating backwards.

b) At 1800 RPM the wheel would appear stationary as they would be in the same position at each time a new frame is captured.