{"id":70,"date":"2012-05-15T00:09:37","date_gmt":"2012-05-15T08:09:37","guid":{"rendered":"http:\/\/www.scimathinstitute.org\/msw\/?p=70"},"modified":"2012-05-15T10:42:53","modified_gmt":"2012-05-15T18:42:53","slug":"air-is-strong","status":"publish","type":"post","link":"https:\/\/www.scimathinstitute.org\/msw\/2012\/05\/15\/air-is-strong\/","title":{"rendered":"Air is Strong!"},"content":{"rendered":"

\"\"<\/a>
\nFigure 1.\u00a0 The vacuum \u201clift\u201d<\/strong><\/p>\n

This is a photo of a science fair project that sought to test how much weight a canister vacuum cleaner could \u201dlift.\u201d\u00a0 It started with a demonstration that can be done with any vacuum cleaner: we tried picking up balls of various sizes.\u00a0 No ordinary shop vac with a normal-sized hose can lift a bowling ball, but with a simple modification, any vacuum cleaner can easily lift a bowling ball.\u00a0 The key to the whole experiment is surface area.<\/p>\n

Before getting into the details, I should point out there really is no such thing as suction<\/strong><\/em> as most people (myself included) think of it.\u00a0 The common thought is that vacuums exert a force that pulls objects into them.\u00a0 Hence the terms \u201clift\u201d \u201csuck\u201d and \u201cpick up\u201d which are often used to describe vacuuming.\u00a0 That is not the case.\u00a0 In actuality, objects entering the hose of a vacuum cleaner are being pushed into it.<\/p>\n

Most people recognize that vacuum cleaners work by blowing air out of the canister, which creates a vacuum inside which in turn, \u201cdraws\u201d air in on the suction side (figure 2).\u00a0 However, many people don\u2019t realize that the low-pressure vacuum inside the canister isn\u2019t actually pulling air into the vac.\u00a0 Instead air near the inlet hose is getting pushed in by the surrounding atmosphere because there is greater pressure outside the canister than in.<\/p>\n

\"\"<\/a>
\nFigure 2.\u00a0 How a canister vacuum works.<\/strong><\/p>\n

Another way to think about it is to consider what happens to a dust bunny when it is vacuumed.
\nThe figure below shows how my mind thinks a vacuum cleaner works: that is, when the hose is placed above a dust bunny, the air rushing into the hose pulls the bunny into the hose.\u00a0 My mind wants to think of suction as a pulling force.<\/p>\n

\"\"<\/a>Figure 3.\u00a0 Wrong concept of suction (it is not a pulling force)<\/strong><\/p>\n

However, what is actually happening when a dust bunny gets \u201csucked\u201d into or \u201cpicked up by\u201d a hose.\u00a0 The object isn\u2019t pulled in at all.\u00a0 Instead, atmospheric air is pushing the object into the hose from underneath.<\/p>\n

\"\"<\/a>Figure 4. Correct concept of suction (a pushing force):<\/strong><\/p>\n

For practical purposes, it may not matter to most people whether the dust bunny is pushed or pulled, only that it comes out from under the end table.\u00a0 However knowing that it is the air pushing objects toward the hose takes on a new level of impressiveness when one observes air holding up a 409 pound box!<\/p>\n

This is how the original experiment went:\u00a0 there was a collection of balls of different mass, each having a diameter larger than the mouth of the hose, that I would ask the students which ones they think a vacuum cleaner could \u201clift\u201d\u00a0 They all make their votes, then we try them one at a time.\u00a0 With the vacuum running, the hose is lowered\u00a0 down onto a ball until it forms a seal, then I attempt to rase the hose with the ball and hose in tact.<\/p>\n

I use a 5 gallon shop style vacuum cleaner, so it easily lifts a racket ball, baseball and softball.\u00a0 It even lifts a 5 pound sand-filled workout ball.\u00a0 But when we get to the bowling ball, the hose forms a good tight seal, but as soon as I try to lift, the seal is broken, end the hose separates from the ball.\u00a0 I then introduce the concept of pressure, and see if we can devise a way to lift the ball.<\/p>\n

P=F\/A<\/strong><\/p>\n

This formula states that pressure is equal to force divided by area.\u00a0 On earth, we have a very dense atmosphere; it exerts a force of 15 pounds per square inch.\u00a0 If you don\u2019t think that is very much, try to remove a glass-carrying suction cup that has been sealed to a smooth floor.\u00a0 It has a surface area of about 7 inches.\u00a0 So when it forms a seal to a smooth surface with the air underneath removed, it takes 100 pounds of force to overcome the air pressure pushing down on it!<\/p>\n

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

The vacuum cleaner experiments illustrates the force of the air pushing on an object as well.\u00a0 When the seal forms between the object and the hose, air pressure pushes on the object to keep the object pressed against the mouth of the hose.\u00a0 And it takes several pounds of force to counter act the pushing force of the atmosphere to break the seal.\u00a0 So if the object is heavy enough, its weight will exert enough force to break the seal.<\/p>\n

Notice from the equation above, however that pressure has to do with both force and area.\u00a0 So, for a given pressure if the area is increased, so is force.\u00a0 So in our experiment, we secure a funnel to the end of the hose to increase the area (figure 6).\u00a0 In so doing, the same air pressure can \u201clift\u201d more weight.<\/p>\n

\"\"<\/a>
\nFigure 5.\u00a0 A funnel increases area to create a larger area of low pressure.<\/strong><\/p>\n

This is an experiment you can try at home.\u00a0 Just make sure the funnel is securely taped to the end of the vacuum cleaner hose, and try lifting up something heavy.\u00a0 Pretty impressive!<\/p>\n

The homeschooler who performed the experiment shown in figure 1 wanted to try an even larger surface area.\u00a0 So he built a disk having a diameter of 18 inches.\u00a0 This created an area over 80 times greater than the hose, and therefore a force over 80 times greater.\u00a0 The picture (figure 1) shows the device being held PUSHED against the disk on top by air pressure.\u00a0 We loaded over 409 pounds in the box before the seal finally broke!<\/p>\n

\"\"<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Figure 1.\u00a0 The vacuum \u201clift\u201d This is a photo of a science fair project that sought to test how much weight a canister vacuum cleaner could \u201dlift.\u201d\u00a0 It started with a demonstration that can be done with any vacuum cleaner: … 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":[5,1],"tags":[],"class_list":["post-70","post","type-post","status-publish","format-standard","hentry","category-physical-science","category-uncategorized"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/posts\/70","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=70"}],"version-history":[{"count":8,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/posts\/70\/revisions"}],"predecessor-version":[{"id":76,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/posts\/70\/revisions\/76"}],"wp:attachment":[{"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/media?parent=70"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/categories?post=70"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.scimathinstitute.org\/msw\/wp-json\/wp\/v2\/tags?post=70"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}