{"id":59,"date":"2012-05-10T00:36:22","date_gmt":"2012-05-10T08:36:22","guid":{"rendered":"http:\/\/www.scimathinstitute.org\/msw\/?p=59"},"modified":"2012-05-10T07:37:09","modified_gmt":"2012-05-10T15:37:09","slug":"magnifying-weight-its-all-about-acceleration","status":"publish","type":"post","link":"https:\/\/www.scimathinstitute.org\/msw\/2012\/05\/10\/magnifying-weight-its-all-about-acceleration\/","title":{"rendered":"Magnifying weight: It\u2019s all about acceleration"},"content":{"rendered":"

\"\"<\/a>
\nPeriodically, I use bathroom scales for experiments.\u00a0 (However instead of calling them scales, I prefer the term forceometer, because they are very good at measuring the gravitational force<\/strong> of attraction between the earth and an object).<\/p>\n

I\u2019ve found that I cannot leave forceometers lying around in the workshop when kids (particularly boys) are present.\u00a0 They cannot avoid the temptation to jump on them to see if they can \u201cpeg\u201d the needle.\u00a0 I can\u2019t fault them too much though, because they are doing good empirical research.\u00a0 And what they find is that it really is not all that hard to have a \u201cweight\u201d over 300 pounds for a very brief time.\u00a0 It\u2019s all in the acceleration<\/strong>.<\/p>\n

Another place to see this phenomenon is with the stomp rocket.\u00a0 Students learn very quickly that there is a direct correlation between force of stomp and distance the rocket travels.\u00a0 What they may not realize that they are simply following Newton\u2019s first law to generate a large force by maximizing acceleration.<\/p>\n

F = ma<\/p>\n

The above formula tells us that force is proportional to acceleration.\u00a0 Acceleration is change in speed, therefore the faster an object\u2019s (or boy\u2019s) speed changes, the larger the force.<\/p>\n

In the picture below, the boy is going to be accelerated by gravity as he free-falls over the entire distance that he falls. Then he is going to lose all his speed<\/em> over a very short distance, so his acceleration will be much higher than gravity.\u00a0 (we\u2019ll talk more about g force in a separate post)<\/p>\n

\"\"<\/a><\/p>\n

If the student were to simply stand on the stop rocket pad, he would exert a force equal to his own weight<\/strong>.\u00a0 With a few calculations, we can estimate how much extra force he will generate by falling from a height of 40 cm.<\/p>\n

Knowing that gravity will accelerate him downward at a rate of 9.8m\/s per second, it is possible to determine that his velocity just before he hits the stomp rocket pad will be about 2.8 m\/sec.\u00a0 When he hits the stomp rocket pad, he will lose all that velocity while traveling only about 7.5 cm, which would take about 6\/100 of a second.\u00a0 So his stopping acceleration would be 21.23 m\/sec per second, which is a little more than twice normal gravity, so he would exert a force of twice his weight<\/strong> by simply free-falling 40cm.<\/p>\n

Everyone knows that stomp-rocketers won\u2019t just free-fall; at the last moment, they\u2019ll forcefully extend their legs to stomp, which cuts the acceleration time in half or a third so that the total force exerted would be four or even six times his own weight<\/strong>.\u00a0 For a 50 lb kid, that could mean a total impact force of 300 pounds, which is enough to peg the needle on my forceometers (bathroom scales).\u00a0 And that is why I\u2019ve learned not<\/em> to leave the forceometers lying around in the workshop, and instead make sure I have plenty of stomp rockets on hand!<\/p>\n","protected":false},"excerpt":{"rendered":"

Periodically, I use bathroom scales for experiments.\u00a0 (However instead of calling them scales, I prefer the term forceometer, because they are very good at measuring the gravitational force of attraction between the earth and an object). I\u2019ve found that I … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[5],"tags":[],"class_list":["post-59","post","type-post","status-publish","format-standard","hentry","category-physical-science"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/posts\/59","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/comments?post=59"}],"version-history":[{"count":5,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/posts\/59\/revisions"}],"predecessor-version":[{"id":69,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/posts\/59\/revisions\/69"}],"wp:attachment":[{"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/media?parent=59"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/categories?post=59"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/tags?post=59"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}