It's common practice to refer to the force that spinning objects exert outward as centrifugal force. Actually, moving objects just "want" to travel in a straight line, but when they spin it means a force keeps forcing them to curve. And--strictly speaking--it is not centrifugal force. Rather...well, I'll just present this e-mail from a young man named London who corrected me. And don't forget to read the hilarious centrifugal force and James Bond cartoon that he brought my attention to.

Hello, I was browsing through your site because I saw it mentioned on some tech related site. I have to say, you've got some very interesting projects that I can't wait to try out. However, I noticed on your page about the helicopter, at one point it says, "When the weights are spun fast, they are subjected to centrifugal force, and people underestimate just how strong it pulls on the weights." Now I'm only a junior in high school, and you're a teacher, but in my AP physics class when we learned about circular motion, we talked about how the centrifugal force doesn't actually exist. The actual force acting on a rotating object is the centripetal force acting towards the center of the orbit from the thing that keeps it in a rotating path, such as the wall of the tip of the helicopter wing pushing the clay towards the center. From my understanding, the apparent "centrifugal" force is just the objects inertia resisting the acceleration towards the center of its orbit. Please correct me if I'm wrong.

Thanks,
London Reinhard

p.s. While writing this I was reminded of a funny cartoon from the web comic xkcd that mentions centrifugal force, you can see it at http://www.xkcd.com/123/

p.p.s Once again, your site is great.

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