In this installment we answer “Why do Fast Spinning Wheels Appear to Spin Backwards?

In this the last week of summer we have a little time to ponder things and ask ourselves, why? Why do fidget spinners appear to spin in reverse.

This is caused due to human persistence of vision. It is called the Stroboscopic Effect or Wagon-wheel effect.

When we see something that is moving, we do not actually see every point in the motion. We capture an image 10-12 times every second, and we use the data that we capture, and using past experience/common logic, we fill in the blanks.

So this is a slower motion.

When a fast spinning fidget spinner (or wheel of a car or the rotor of a helicopter) is spinning it is a much faster movement and depending on the speed, we capture random points of rotation. So it could appear that it is spinning the opposite direction, the same direction but slower, or even not moving at all.

So since the rotation is faster than what the eye can capture, it may appear that the rotation is actually in the opposite direction.

As the speed of rotation changes, the apparent direction of rotation will also change.

Thus when a car accelerates, the tires appear to move forward, then slow down, then rotate the opposite direction.
This is all because of fast rotation (faster than the eye can see) and human persistence of vision.