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Welcome to the Greenwood.Net Curiosity Corner

Centrifugal Force and Green Eggs

Sep 19, 2018

Curiosity Corner
By
Dr. Jerry D. Wilson,
Emeritus Professor of Physics
Lander University

Question: I enjoy your column and look forward to it every Sunday. My question for you is this: Is there centrifugal force in space? If not, why? If so, does it differ in any way from centrifugal force on earth? [Asked by Steve Hill, O.T. (Occasional Thinker), via cyberspace.]

Reply: Good question – a little physics. When we studied circular motion in my physics classes and my students asked me about centrifugal force, I would tell them that it doesn’t exist; that it’s a pseudo— or false—force. That is, in applying Newton’s first law of motion—an object will remain at rest or in uniform motion in a straight line unless acted upon by an external, unbalanced force.

But wait, you say! Suppose you are swinging a stone on a string in a horizontal plane, and there’s an outward pull or force. Isn’t this a centrifugal force?

Well, let’s look at the system. The string exerts a force on the stone to keep it traveling in a circle. Otherwise, it would travel in a straight line by Newton’s first law. This is a real centripetal (center-seeking) force. Neglecting gravity (which is balanced by an upward string component), this is the only string force acting on the stone—a real centripetal force that keeps the stone moving in a circle. If the string breaks, the stone would fly off, a la Newton.

Now, take a look from the stone’s point of view. There is the inward force of the string acting, but in the stone’s reference system it is not moving in that direction, so there must be a balancing force in the opposite outward direction—a centrifugal (center-fleeing) force. That is, in the rotating system, there is an apparent force away from the center of rotation. It is an apparent force in the rotating system.

Looking at it from what you see (your frame of reference), this force doesn’t exist. When you swing the stone, you say you feel an outward force. This is Newton’s third law—equal and opposite forces. You exert a force on the string, and the string exerts a force on you. There is only one inward centripetal force exerted by the string on the stone, which keeps it in orbit via Newton’s second law through a centripetal acceleration toward the center.

So there is an apparent centrifugal force, in space or otherwise, depending on how you look at things.

That one was physics, so let’s do a little chemistry.

Question: I cut open a hard-boiled egg and there was a green ring around the yolk? What is it? Is this safe to eat? (Asked by a concerned chef.)

Reply: When you cut open a hard-boiled egg and see a greenish, blackish ring around the yolk, it’s a sign that the egg was overcooked. The greenish dark ring is evidence of the formation of iron sulfide where the white and yolk parts of the egg meet. Iron from the yolk reacts with hydrogen sulfide from the white when the egg is cooked too long. The egg is still okay to eat—just don’t cook it so long next time!

C.P.S. (Curious Postscript): When science finally locates the center of the universe, some people will be surprised they’re not it. –Bernard Bailey

Curious about something? Send your questions to Dr. Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC 29649, or email jerry@curiosity-corner.net. Selected questions will appear in the Curiosity Corner. For Curiosity Corner background, go to www.curiosity-corner.net.

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