Tuesday, January 10, 2012

The Fictitious Force

Picture this: you're driving in your car, with some item on the seat next to you. Let's say it's your cell phone. As you scoot on down the highway, all is right with the world. Your CD of Songs From a Colonial Tavern, by Taylor Vrooman*, has you bobbing your head gleefully.

You come upon an exit and need to pull your car onto the side road. As you veer off you hear the sound of you phone sliding sideways across the seat and clunking against the passenger door, then dropping onto the floor. "Why", you ask yourself, "did my phone going flying off to the right?"
"What pushed it over there?" It's only natural to ask those questions and wonder what happened.

The problem is that there is no good, direct answer because the questions are poorly worded. Nothing pushed the cell phone across the seat. However, we were most likely taught that something called centrifugal force was behind the mysteriously sliding cell phone. We were incorrectly taught that centrifugal force pushed the phone to the right while you put your car into a left-hand turn. The same force supposedly caused us to go flying off of the Merry-go-round in third grade. Unfortunately, there is no such thing as centrifugal force. So what happened, and how do we explain this?

To learn what happened we have to invoke Isaac Newton, and his three laws of motion. To put this as simply as possible for the purposes of this writing, the cell phone was traveling in a straight line along with the speeding car, but the car decided, at your insistence, to move out from under the cell phone. All objects in motion, like the car and phone, will continue to move in a constant direction unless acted upon by an external force.

In this case, your car was acted upon by friction; friction of the tires against the road surface caused your car to change its direction. Your tires were able to create enough grip, or friction, to redirect the movement of your previously straight-moving car. So it turned left. However, your cell phone and the seat it was resting on were not able to generate enough friction to change the direction of travel of the phone, therefore it continued to move in the direction it had been moving, as per Newton's First Law. Nothing pushed it. It was simply continuing to do what it had been doing.

So why were we most likely taught that something pushed the phone off the seat? I'm not exactly sure, but I think that answer to that has to do with many factors, including, but not exclusive to, laziness, lack of knowledge of real physical forces, teaching to the lowest common denominator (don't crucify me for being the messenger on that one!), and intellectual inertia. It's just easier to explain the phenomena through the simplest means rather than to have to go into more and more detail.

In order to really grasp what really happens, you would have to be taught more things, like those pesky laws of motion, friction, force, mass, acceleration, and the real force - centripetal force. It's time consuming and, in the long run, you can live your life to the fullest without having to know all that extra stuff. That's why I'm guessing we weren't taught properly. But I could be wrong.

Speaking for myself, I'd rather go to the trouble of learning all of that "extra stuff". Because I'd prefer to know how the world really works, even if I don't actively use that information on a daily basis, or ever. I simply want to know how things really are, and I am a little bit annoyed that our institutions of education don't always feel the same way. I know. Picky, picky, picky. Sue me.

Next week: centripetal force, or why a lack of something can cause another thing to happen.

* If anyone but me actually owns this, that person should be very ashamed. I know I am.


  1. I have never wondered why it flies off the seat, just have always been annoyed when it does. Thanks for 'splaining it to me.

  2. Does this have something to do with why I can't seem to move off the couch lately?

  3. @nubian: The force of annoyance may be even stronger than the force of inertia, or curiosity!

    @dbs: You obviously have read ahead a chapter or two! That's in my chapter on Corn Chips, Drinks Which Contain Hops, Mass, and Inertia.