Curiosity Corner: Clockwise, Counterclockwise

Curiosity Corner

By

Dr. Jerry D. Wilson,

Emeritus Professor of Physics

Lander University

Question: While sitting, lift your right foot and make clockwise circles. While doing that, draw a “6” in the air with your right hand. Your foot will change direction, and there’s nothing you can do about it. I tried it, and my food did indeed go back the other way. What causes this? (Asked by a curious column reader via cyberspace.)

Reply: This is an old one! I think I addressed it years ago, but let’s have some fun and do it again with a little experimenting. It’s true that normally, when you are sitting and rotating your right foot clockwise, and then draw a figure 6 in the air with your right hand, your leg will jerk and start in the other direction. (You can do these movements with the opposite foot and hand if you are left footed.)

Now, rotate your foot clockwise again and at the same time, rotate your right hand in the air clockwise. What happens? You should have a couple of nice, continuous rotations.

Now, start rotating your hand counterclockwise. There’s the jerk and reverse foot direction again! This reverse direction is essentially what you do when you draw a figure 6. The first movement is in the six is counterclockwise. You can do the same thing starting the foot and hand in the counterclockwise directions and then reversing the hand direction clockwise.

As explained to me, the motor control center on the left side of the brain controls the right side of the body (and vice versa). When you are moving your right foot in a clockwise circular path, while trying to make a figure 6 with your right finger, you are using the same (left) side of the brain, and it has trouble discerning the prior rotational foot command.

From our experiment, it looks like a nerve-muscle interaction. When the foot and the hand are rotating in the same direction, the muscles and nerves are in coordination. However, when you want to make a voluntary change in the arm direction, the brain fires off nerve impulses to the arm muscles to do this. But the impulses also affect the leg muscles and attempt to facilitate the leg to move in the same rotational direction as the arm. Hencethe jerk and attempted change in leg rotation.

This doesn’t occur when the foot and finger rotations are in the same direction. To see this nerve-muscle interaction more clearly, rotate the right foot clockwise and draw a figure 8 in the air with the hand. I don’t know about you, but I get a foot jerk or some sort of figure 8 motion.

This is just my take on the phenomenon as an experimental physicist. A neurologist could no doubt give a more detailed, and perhaps more correct explanation. Here’s another one you can try: simultaneously rotate the index fingers of both hands clockwise. Do it slowly at first, then speed up, faster and faster. Pretty soon, the fingers will be going in the opposite directions. I’ll let you explain that one.

C.P.S. (Curious Postscript): “Man was made at the end of the week’s work when God was tired.” -Mark Twain

Curious about something? Email your questions to Dr. Jerry Wilson at curiosity.corner@yahoo.com. Selected questions will appear in the Curiosity Corner.