tag:blogger.com,1999:blog-23903680.post5478637817940920898..comments2023-06-27T06:49:13.340-05:00Comments on Drew's Day: How powerful is a physics professor, anyway?Unknownnoreply@blogger.comBlogger4125tag:blogger.com,1999:blog-23903680.post-39659509098547380632010-02-17T11:53:42.592-06:002010-02-17T11:53:42.592-06:00That's an interesting idea!
I once heard a ...That's an interesting idea! <br /><br />I once heard a talk by someone who was developing a sensor to measure the motion of humans walking, and they were making use of the periodicity, similar to what you are talking about. So I don't doubt that there may be something to your observation and explanation.<br /><br />I'm just concerned that my hasty clicking on the video may have introduced measurement uncertainties that would make any analysis of the oscillations somewhat ambiguous to interpret. <br /><br />I should go back and see what the acceleration curve looks like. Thanks for the idea!Andrewhttps://www.blogger.com/profile/05546307689313619934noreply@blogger.comtag:blogger.com,1999:blog-23903680.post-2783477440650265042010-02-17T10:52:13.876-06:002010-02-17T10:52:13.876-06:00The variations in the force graph display a period...The variations in the force graph display a periodicity of about 1.5 seconds, which appears to be about the length of time it takes to step with both feet.<br /><br />I would hypothesize the variations in force are related to footfalls.<br /><br />Humans evolved for walking because it is efficient, using a upside-down pendulum approach to convert potential energy into kinetic energy and then back again (as a pendulum does).<br /><br />Something similar is happening here. One of his legs acts as a lever, with a fulcrum at the foot. As his center of mass lowers, that lever converts the potential energy of his hight into kinetic energy accelerating the car.<br /><br />As he walks away, chemical energy in his muscles is converted into potential energy as he reestablishes the hight of his center of mass.<br /><br />So, since his walking is a periodic process, with a varying output of kinetic energy, one would expect the car's rate of acceleration to be periodic.<br /><br />Additionally, as the car accelerates, so too must the rate of footfalls (indeed, for the first couple of seconds he doesn't step at all) and so you would expect the periodicity of the output to cycle faster and faster as his steps become faster and faster.<br /><br />And the second graph displays a lovely sine wave like curve, relative to the slope of acceleration, which increases in frequency over time. (Just as I would expect, if all of the above assumptions are true.)<br /><br />It would be interesting to see how your data points compare to the position of his feet at that moment in time.<br /><br />Actually, I'll bet plotting his center of mass would result in the same sine curve seen in the graph of the car's acceleration, or to a closely correlated sine curve.<br /><br />I failed college physics BTW. Did fine with all the concepts but hated all the math.Unknownhttps://www.blogger.com/profile/04993969488611970526noreply@blogger.comtag:blogger.com,1999:blog-23903680.post-71061298180266264032010-02-10T11:38:38.856-06:002010-02-10T11:38:38.856-06:00I don't know how long the (nearly) constant ac...I don't know how long the (nearly) constant acceleration lasts. I was running out of time while working on the Logger Pro video tracking, so I gave up after I felt I had enough data.Andrewhttps://www.blogger.com/profile/05546307689313619934noreply@blogger.comtag:blogger.com,1999:blog-23903680.post-88358932103150548902010-02-10T10:46:08.240-06:002010-02-10T10:46:08.240-06:00See how strong I am? This means, don't mess w...See how strong I am? This means, don't mess with physics dudes.<br /><br />And yes, the units are strange. I did this to match up with the crazy ESPN Sport Science episode that I was attacking.<br /><br />This is a pretty good analysis. 300 Newtons seems like a reasonable value - but the more interesting thing is the acceleration. I didn't even think about the idea that this would produce a pretty constant acceleration.rallainhttps://www.blogger.com/profile/12956503928971828628noreply@blogger.com