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By pressing a rice bowl on his abdominal muscles, Zhang Xingquan was able to create enough suction to pull a 36.15 tonnes heavy train for 40 meters

Source: Guinness world records website.

How does the bowl 'attach' to his abdominals and not fall down as he walks backwards? How is he able to use suction to pull such a heavy object?

A video can be found here.

hb20007
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    Looks like he is simply expanding his stomach, then contracting it in order to reduce the pressure inside the bowl. The pressure difference between the bowl inside and outside will do the rest. – valerio Jun 23 '16 at 10:45
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    Possible duplicate : How do suction cups work? http://physics.stackexchange.com/q/199721. Insufficient research effort (-1). – sammy gerbil Jun 23 '16 at 10:49
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    Possible duplicate of How do suction cups work? – Danu Jun 23 '16 at 11:02
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    I just voted you up cause apart from the principles there is the matter of myth or fact busting. See my answer below. Someone check me on the math, but this appears to be a myth - busted!! Perhaps the bowl was full of crazy glue. – docscience Jun 23 '16 at 15:16
  • Regarding your edit: a rice bowl is not flexible, but Mr. Zhang clearly is. He is a suction cup in principle, so your question is answered the same as "how do suction cups work?" – Asher Jun 23 '16 at 16:21

2 Answers2

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The exact mechanism you describe for how suction cups work is how the rice bowl work. Instead of the bowl being flexible, though, it's his body (skin and muscles) that are providing the change in volume necessary for the suction. So, instead of the suction cup creating the volume change, it's the surface the suction cup (the bowl) is attached to, Mr. Zhang's very impressive abs.

All you need for suction is for the air pressure inside the bowl to be less than the air outside the bowl. I presume that Mr. Zhang accomplishes this by filling as much of the bowl as he can with his own skin and muscle, and then uses impressive abdominal strength to pull that skin and muscle back, increasing the volume accessible to the air in the bowl and thus decreasing its pressure.

Also note that Mr. Zhang has a strap that helps hold the bowl to his gut. I am not implying that this strap is being used to actually hold the bowl onto his gut, but probably more to keep the bowl positioned well enough so that the suction is not broken.

NeutronStar
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  • Could you provide more details about how his skin and muscles are able to create the suction? I have tried to replicate creating this suction to no avail – hb20007 Jun 23 '16 at 12:02
  • Does the shape of the bowl matter too? – hb20007 Jun 23 '16 at 12:15
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    @hb20007, the only way I can think that the shape of the bowl would be important is whether the shape makes it easy to fill the bowl's volume with skin and muscle and then pull that skin and muscle back to create suction. – NeutronStar Jun 23 '16 at 14:58
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We must all keep in mind that for average atmospheric pressure, and assuming Zhang could pull a hard vacuum with his abdomen (which is probably not feasible, but serves to provide us with a bound), the maximum (negative) pressure he could achieve is only about 14.7 psia.

Given 36 tonnes, you can back calculate what the diameter of the bowl would have to be. It turns out to be about 80 inches in diameter. And that doesn't even take into account any frictional forces that have to be overcome.

So Zhang either has a tremendously large abdomen (and a large rice bowl to match!) or something is amiss in the record reporting.

docscience
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    If the train is rolling, you only have to overcome the rolling friction, not the full weight of 36 tonnes. Which is not to say it isn't still very heavy, but I don't think 36 is the right number to use for the force required. – tpg2114 Jun 23 '16 at 15:16
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    I second @tpg2114's comment. If Mr. Zhang were holding the train up off the ground, then he would definitely need 36 tonnes of support. With the train on the ground, all he would need to overcome is the static friction. I don't know much about train engineering and lubrication, but it's possible the train was well-lubricated specifically to help Mr. Zhang accomplish his impressive feat. – NeutronStar Jun 23 '16 at 15:32
  • So how big is the bowl? Do the direct calculation to estimate the load! – docscience Jun 23 '16 at 15:57