{"id":10048,"date":"2015-05-21T10:21:36","date_gmt":"2015-05-21T14:21:36","guid":{"rendered":"http:\/\/scienceblogs.com\/principles\/?p=10048"},"modified":"2015-05-21T10:21:36","modified_gmt":"2015-05-21T14:21:36","slug":"breaking-boards","status":"publish","type":"post","link":"http:\/\/chadorzel.com\/principles\/2015\/05\/21\/breaking-boards\/","title":{"rendered":"Breaking Boards"},"content":{"rendered":"<p>One of the highlights of teaching introductory mechanics is always the &#8220;karate board&#8221; lab, which I start off by punching through a wooden board. That gets the class&#8217;s attention, and then we have them hang weights on boards and measure the deflection in response to a known force. This confirms that the board behaves like a spring, and you can analyze the breaking in terms of energy, estimating the energy stored in the board, and the speed a fist must have to punch through the board. As a sort of empirical test, we can drop a half-kilogram mass from the appropriate height to match the calculated speed, and see if it goes through.<\/p>\n<p>As mentioned <a href=\"http:\/\/scienceblogs.com\/principles\/2015\/05\/19\/toy-roller-coasters-and-the-energy-principle\/\">earlier this week<\/a>, I have a camera that shoots high-speed video now, so of course I decided to get a shot of the breaking boards:<\/p>\n<p><iframe loading=\"lazy\" width=\"560\" height=\"315\" src=\"https:\/\/www.youtube.com\/embed\/ZkHXZYvd2qg\" frameborder=\"0\" allowfullscreen><\/iframe><\/p>\n<p>It&#8217;s interesting to see how quickly the break happens&#8211; this is shot at 1000 fps, and between one frame and the next, the board goes from solid-but-bent to broken more than halfway through. It&#8217;s also interesting that in the second break shown in the video, the break occurs at a point a good deal away from the spot where the mass hits.<\/p>\n<p>And, of course, there&#8217;s the obligatory gag reel at the end, from one of the several shots where the board didn&#8217;t break, and the mass bounced up to knock over the big demo caliper set that I propped up to provide a reference scale behind the board. Good times, good times&#8230;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>One of the highlights of teaching introductory mechanics is always the &#8220;karate board&#8221; lab, which I start off by punching through a wooden board. That gets the class&#8217;s attention, and then we have them hang weights on boards and measure the deflection in response to a known force. This confirms that the board behaves like&hellip; <a class=\"more-link\" href=\"http:\/\/chadorzel.com\/principles\/2015\/05\/21\/breaking-boards\/\">Continue reading <span class=\"screen-reader-text\">Breaking Boards<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":10049,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[134,13,19,7,11,136],"tags":[],"class_list":["post-10048","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-course_reports","category-education","category-experiment","category-physics","category-science","category-video","entry"],"_links":{"self":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/10048","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=10048"}],"version-history":[{"count":0,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/10048\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/media\/10049"}],"wp:attachment":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/media?parent=10048"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/categories?post=10048"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/tags?post=10048"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}