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Suppose that for some reason gravity magically changes, but only for people. While this goes on, instead of gravity pulling people down, it pushes them East. To be clear, it's just people. Not animals, not objects, and not their buildings. People fall east, but everything else falls to Earth like normal.

My understanding of construction and materials is that there are a lot of things that can handle insane amounts of a certain type of force, from a certain direction, but change the type of force or the direction it pushes in and suddenly the material or structure falls apart like a card castle. Would this happen here?

If this happened in the middle of a normal business day at some large skyscraper, filled to the normal acceptable capacity, and then everyone inside of it suddenly started being pushed sideways instead of pulled down, would the skyscraper still stay up, or would that amount of human weight pushing it sideways be more than it could handle?

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    $\begingroup$ I may have some research on this. To be clear: you are only interested in the exterior structure, or are interior walls also of concern? $\endgroup$
    – Weckar E.
    Jun 28, 2019 at 2:48
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    $\begingroup$ @WeckarE. I can't deny it would make me very happy to see an answer that also discussed interior walls, but that's an unfairly broad topic considering the variety of things they can and are made out of. So yes, let's just focus on exterior structure, the general thing not tipping over from the sideways force of people-gravity. $\endgroup$
    – Simon Price
    Jun 28, 2019 at 2:52
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    $\begingroup$ Windows would go first, wouldn't they? The main problem here isn't the super structure, it's the fact that the walls and windows weren't made for it on individual levels. $\endgroup$
    – Halfthawed
    Jun 28, 2019 at 2:52
  • $\begingroup$ How large a force would seem to be an important factor to consider, or are you asking about the limits of current building tech? $\endgroup$
    – Escaped dental patient.
    Jun 28, 2019 at 2:52
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    $\begingroup$ xkcd.com/417 $\endgroup$
    – The Square-Cube Law
    Jun 28, 2019 at 16:21

3 Answers 3

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According to Evolution of Concrete Skyscrapers: from Ingalls to Jin mao...

It's extremely Unlikely.

The force needed to to effectively topple a modern sky scraper would be about 30% of its weight (above the 1st floor or so) in any direction perpendicular to a shear wall. This is for all skyscrapers built in the late 50s onwards, older buildings which exceed 15 stories will be a different story.

This is because modern sky scrapers actually use tension to keep the shear forces in check. For example, with high wind conditions, The side of the building which is down wind actually has the most tension, due to what the author calls cantilevered systems.

So what would it take to topple a mammoth? well, if you had a high rise which was 100 stories high, and 200 people on each floor, weighing an American Average of 197 lbs, gives us a whopping 1,970 imperial tons. Considering the average skyscraper weighsaround 225,000-250,000 tons (let's say 50% of the weight is below the 1st floor), the people would only weigh 3.57% of the force needed to break the tension system and cause critical failure.

The much more likely instance is the breaking of every window of the building (or close to).

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    $\begingroup$ Thanks so much for providing numbers! $\endgroup$
    – Simon Price
    Jul 5, 2019 at 0:52
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Reinforced concrete and structural steel are not so strongly directional as, for instance, carbon fibers. They would handle a change of load better than, for example, the suspension arm of a F1 car, which can withstand tons of load in the vertical direction but shatters with a minimal horizontal load.

And if you think of it, it must be like that, unless you want your skyscraper to collapse with the first strong wind that blow around.

However there is a problem: windows would become the standing surface for all the people in the outside facing rooms. I don't think that a window is designed to sustain that type of load. Same would happen for some internal non structural walls. I.e. the 25 floors building where I work, most internal walls are made of drywall, not exactly an excellent material to sustain standing people.

So, the building would stand, and the eccentric load given by the East attracted humans would be quickly thrown off the building by the shattering windows and internal partition.

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    $\begingroup$ @WeckarE., that already is covered when designing for wind load, which also gets stronger the higher one goes. $\endgroup$
    – L.Dutch ♦
    Jun 28, 2019 at 2:59
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    $\begingroup$ @WeckarE. they should have about the same order of magnitude. My point is the the glass surfaces would break down before the lateral load on the carrying structure would become significant. $\endgroup$
    – L.Dutch ♦
    Jun 28, 2019 at 3:10
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    $\begingroup$ That would be a horrifying way to die if you think about it. Falling out of a skyscraper, nothing to hit, nothing pulling you back to Earth... but the centrifugal force of constantly being pushed perpendicular to the planet would eventually, slowly, push you out into space. Of course, you'd be dead long before that, but it's a terrifying thought regardless. $\endgroup$
    – Simon Price
    Jun 28, 2019 at 3:18
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    $\begingroup$ @L.Dutch Not at all. They outstrip the people load by an order of magnitude. Example calculation of 47 pounds per square foot: madsci.org/posts/archives/2003-11/1069548418.Eg.r.html $\endgroup$
    – SurpriseDog
    Jun 28, 2019 at 3:18
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    $\begingroup$ Some people would probably avoid being thrown out by hanging on furniture. If it is heavy enough or fixed to the ground, it should be able to stop them from moving. $\endgroup$
    – Eth
    Jun 28, 2019 at 10:25
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The sky-scraper would not even care

Because otherwise people could bring down skyscrapers with their own bodyweight

Think about it this way: If I run as fast as I can and jump against a wall, I can create more force than my usual body-weight due to gravity. Now - if a skyscraper could be brought down by some hundred people running and jumping against the wall we would have a serious problem! - Sky scrapers can resist a whole lot more force.

Maybe some people would create more force, if they fell more than 15 meters sideways without hitting anything before hitting the outer wall, but they will not change the order of magnitude.

Think of 9/11 where a whole plane full of people hit a building sideways and it did not topple over by the impact and this was tons of steel in addition to the people inside the plane.

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    $\begingroup$ Not to mention take off and landing velocity is roughly 150 mph. We didn't even see the buildings sway. $\endgroup$
    – Kai Qing
    Jun 28, 2019 at 19:02
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    $\begingroup$ Do... Do you have a source that a skyscraper won't fall over if you convince every person working in the building to run at the walls and jump at them? Because that's "software engineer" levels of edge-case and definitely outside of reasonable need. And you're asserting without backup that you can't topple a building with the people inside $\endgroup$
    – Delioth
    Jun 28, 2019 at 19:59
  • $\begingroup$ @Delioth if the empirical evidence of skyscrapers not falling over and common sense is not enough for you, you should maybe ask on sceptics.se. - The essence of related papers is that a modern skyscraper cannot really fall over, because it is not really a tower standing on the ground, but deply rooted in its foundation, so skyscrapers will rather crumple than fall over. $\endgroup$
    – Falco
    Jul 1, 2019 at 8:14
  • $\begingroup$ @Falco So do you have a source that skyscrapers won't crumple if everyone in them jumps at the walls? The wording I used doesn't matter, you're still asserting that a skyscraper can withstand any horizontal force that all its occupants can exert. We know for a fact that engineers have avoided accounting for factors or scenarios in the past, which is why several libraries sink (the architects didn't consider the weight of the books). $\endgroup$
    – Delioth
    Jul 1, 2019 at 14:16

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