{"id":9659,"date":"2014-11-06T09:07:46","date_gmt":"2014-11-06T14:07:46","guid":{"rendered":"http:\/\/scienceblogs.com\/principles\/?p=9659"},"modified":"2014-11-06T09:07:46","modified_gmt":"2014-11-06T14:07:46","slug":"playground-physics-angular-momentum-video-homework","status":"publish","type":"post","link":"http:\/\/chadorzel.com\/principles\/2014\/11\/06\/playground-physics-angular-momentum-video-homework\/","title":{"rendered":"Playground Physics: Angular Momentum, Video Homework"},"content":{"rendered":"<p>I&#8217;m teaching relativity in a course with an astronomy prefix, which means I&#8217;m obliged to talk about stars and stuff. Yesterday&#8217;s lecture was about neutron stars, and how their existence was confirmed by the discovery of pulsars (with <a href=\"http:\/\/www.bigear.org\/CSMO\/HTML\/CS01\/cs01p16.htm\">the story of Jocelyn Bell Burnell<\/a> included). This requires some discussion of angular momentum to explain how something that big ends up spinning that fast (cribbing a bit from <a href=\"http:\/\/frigg.physastro.mnsu.edu\/~eskridge\/astr101\/week10_3.html\">these online notes<\/a>), so I needed a good demonstration of angular momentum. Which is when I remembered <a href=\"http:\/\/scienceblogs.com\/principles\/2013\/04\/24\/playground-physics\/\">this 2013 post with SteelyKid on the playground<\/a>, where I estimated the mass of the merry-go-round at the JCC from how the rotation changed as she moved.<\/p>\n<p>Of course, that effect isn&#8217;t as dramatic as it could be, because her mass is pretty small. It would work a lot better with my fat ass on the merry-go-round; and, indeed, it turns out I have video of that:<\/p>\n<p><iframe loading=\"lazy\" width=\"560\" height=\"315\" src=\"\/\/www.youtube.com\/embed\/GoByVGNsX5g\" frameborder=\"0\" allowfullscreen><\/iframe><\/p>\n<p>My mass is considerably larger than SteelyKid&#8217;s, so when I move to the center, you get a much more pronounced increase in rotation rate. In fact, there&#8217;s an outtake of this where she spun it up too fast, and I was unable to drag myself all the way to the center against the centrifugal force. Also, I got really dizzy, and had to sit down for a bit&#8230;<\/p>\n<p>Anyway, if I were using this in a majors course, I&#8217;d go through the calculation of the monments of inertia and all that. This is a Gen Ed class, though, and I&#8217;m crazy busy. But that doesn&#8217;t mean you can&#8217;t do it for homework. So, your assignment, should you choose to accept it, is to determine the mass of the merry-go-round from the above video. You need some numbers for scale, so I am almost exactly 2m tall (definitely, in sneakers), and my mass is around 127 kg.<\/p>\n<p>Is the mass you estimate from this video and those numbers consistent with my earlier estimate? What systematic sources of uncertainty are there in this calculation? Type your calculation up in no more than 5 single-spaced pages, and send it to <a href=\"http:\/\/www.wired.com\/category\/science-blogs\/dotphysics\/\">Rhett<\/a> for grading.<\/p>\n<p>(This video was shot back in April, when we also looked at the <a href=\"http:\/\/scienceblogs.com\/principles\/2014\/04\/28\/non-inertial-playground-physics\/\">Coriolis effect<\/a> on the merry-go-round, but I didn&#8217;t upload it until yesterday when I wanted it for class&#8230;)<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I&#8217;m teaching relativity in a course with an astronomy prefix, which means I&#8217;m obliged to talk about stars and stuff. Yesterday&#8217;s lecture was about neutron stars, and how their existence was confirmed by the discovery of pulsars (with the story of Jocelyn Bell Burnell included). This requires some discussion of angular momentum to explain how&hellip; <a class=\"more-link\" href=\"http:\/\/chadorzel.com\/principles\/2014\/11\/06\/playground-physics-angular-momentum-video-homework\/\">Continue reading <span class=\"screen-reader-text\">Playground Physics: Angular Momentum, Video Homework<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":9660,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10,678,663,19,7,11,136],"tags":[],"class_list":["post-9659","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-astronomy","category-estimation","category-everyday","category-experiment","category-physics","category-science","category-video","entry"],"_links":{"self":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/9659","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/comments?post=9659"}],"version-history":[{"count":0,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/9659\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/media\/9660"}],"wp:attachment":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/media?parent=9659"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/categories?post=9659"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/tags?post=9659"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}