What-If 0133: "Flagpole"

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chris857
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What-If 0133: "Flagpole"

Postby chris857 » Wed Mar 18, 2015 3:47 am UTC

Flagpole

Image

Welp. That was a set of pretty frightening mental images. I suggest less injurious ways of saving oneself.

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Re: What-If 0133: "Flagpole"

Postby Pfhorrest » Wed Mar 18, 2015 3:56 am UTC

I was hoping he would also go into detail on the rest of the steps in that maneuver, such as the difficulty of aiming your descent at the flagpole to begin with, and then (assuming you somehow did that and the impossible grab) how much height you could expect to get up the ascent after the grab, and again the difficulty at aiming yourself such that you end up on the roof (assuming you even get enough height for that) instead of just in the middle of the air and falling again.
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Re: What-If 0133: "Flagpole"

Postby SuperSteve » Wed Mar 18, 2015 4:15 am UTC

Did he calculate the strength of a flagpole? I'm not so sure that the drawing showing the person falling with the arms left behind on the flagpole is right. I think it's possible you might just tear the flagpole off the building. Either way, you're going to die, but the reasoning may be faulty.

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Re: What-If 0133: "Flagpole"

Postby mccdyl001 » Wed Mar 18, 2015 5:29 am UTC

Came to say the same as SuperSteve.

Some quick estimating has 3kN = 700lb or 350kg in proper units. So 10kN = 1 ton. 100kN = 10 tones. Of nearly instant downward force. On a flagpole sticking out the side of a building? That thing is either bending or pulling out the wall long before the arms are torn off.

My question is, what if the flagpole just bends and smoothly pivots the fallee into the side of the building. Would the fallee have enough strength to hold on? And if its into a plate glass window, would it absorb enough of the impact to not kill the fallee? (I'm thinking the first matrix movie, the helicopter scene on the roof where Trinity is falling and grabs onto the tether Neo is holding and then slams into the glass). Or if it was an old style building with big open windows, what are the odds of being ejected into a modern office with a lateral speed close to 100mph...

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Re: What-If 0133: "Flagpole"

Postby Sir Real » Wed Mar 18, 2015 7:06 am UTC

It's hard to find good numbers on how much force it takes to tear off a person's arm.


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Re: What-If 0133: "Flagpole"

Postby Tub » Wed Mar 18, 2015 7:46 am UTC

That's why you use a grappling hook on the flagpole. Amateurs. :roll:

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Re: What-If 0133: "Flagpole"

Postby Quercus » Wed Mar 18, 2015 9:58 am UTC

Tub wrote:That's why you use a grappling hook on the flagpole. Amateurs. :roll:


A grappling hook with a bungee cord... I think we just invented a new extreme sport :)

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Re: What-If 0133: "Flagpole"

Postby ThatPITA » Wed Mar 18, 2015 10:25 am UTC

Even if your arms and the flagpole could bear the stress, you would never reach the roof. Like a bouncing ball, the flagpole maneuver would dissipate energy and you would ascend to a lower level than when you started. Then gravity would re-assert itself and you would head back down, albeit at a lower speed (because of your lower start point). If you could keep this up long enough, you'd end up clinging to the flagpole, awaiting rescue. Except that anyone who was watching would be too busy capturing video on their phone to call for help. Or - and yes I am a cynic - they'd be pointing their phones at you, waiting for your arms to tire and finish the other half of your trip.

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Re: What-If 0133: "Flagpole"

Postby jeanrenaud » Wed Mar 18, 2015 11:35 am UTC

I think the fingers would be the first thing to break, if any body part breaks. There could be some shoulder dislocation at one point (if the fingers do not get cut off before).This link states that "Shoulder dislocation" can happen by "a fall on an outstretched arm" or "when the arm is pulled or twisted with extreme force in an outward, upward or backward direction".
http://www.drugs.com/health-guide/shoulder-dislocation.html

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Re: What-If 0133: "Flagpole"

Postby ...m... » Wed Mar 18, 2015 11:56 am UTC

...i can speak from first-hand experience, having attempted this myself just to see what happens...

...i leapt from the top of a hayloft and tried to catch myself on a rafter several feet below, a total vertical displacement of about eight feet, and the energy was almost entirely bourne through my shoulder sockets, which hurt like hell in the split-second before my grip snapped from the rafter under load and i fell into the hay pile below...

...gymnastic uneven parallel bars are set with only about thirty inches of vertical displacement, but i think a much better-suited example for this sort of maneuver would be an extreme brachiating primate species, like a gibbon, to observe the median and maximum vertical drop achieved in nature...

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Re: What-If 0133: "Flagpole"

Postby Barstro » Wed Mar 18, 2015 12:30 pm UTC

What about a spherical flag pole in a vacuum? Then could it be done?

The question reminded me of this;
Spoiler:
Two men are sitting drinking at a bar at the top of the Empire State Building, when the first man turns to the other and says "You know, last week I discovered that if you jump from the top of this building, the winds around the building are so intense that by the time you fall to the 10th floor, they carry you around the building and back into a window". The bartender just shakes his head in disapproval while wiping the bar.

The second guy says, "What, are you nuts? There's no way that could happen."

"No, its true," the first man says. "Let me prove it to you." He gets up from the bar, jumps over the balcony, and plummets toward the street below. As he nears the 10th floor, the high winds whip him around the building and back into the 10th floor window and he takes the elevator back up to the bar.

He meets the second man, who looks quite astonished. "You know, I saw that with my own eyes, but that must have been a one time fluke."

"No, I'll prove it again," says the first man as he jumps again. Just as he is hurtling toward the street, the 10th floor wind gently carries him around the building and into the window. Once upstairs he urges his fellow drinker to try it.

"Well, why not." the second guy says, "It works. I'll try it." He jumps over the balcony, plunges downward passes the 11th, 10th 9th, 8th, floors. . . . . and hits the sidewalk with a SPLAT.

Back upstairs the bartender turns to the other drinker and says, "You're a real jerk when you're drunk, Superman".

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Re: What-If 0133: "Flagpole"

Postby mathmannix » Wed Mar 18, 2015 12:54 pm UTC

Barstro wrote:
Spoiler:
"You're a real jerk when you're drunk, Superman".

I hear velociraptor tastes like chicken.

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Re: What-If 0133: "Flagpole"

Postby Pyure » Wed Mar 18, 2015 1:26 pm UTC

I'm curious, what would happen if you were falling from some monstrous height and saw a vertical flagpole nearby? Could you grasp that lightly enough that you could arrest your speed significantly?

I imagine you'd just end up bouncing off it despite your best efforts.

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Re: What-If 0133: "Flagpole"

Postby Wiz » Wed Mar 18, 2015 1:47 pm UTC

I'm a bit disappointed this "What If" didn't end with a scenario a la #43 (Train Loop) where the jumper's arm strength, the pole's strength & length & flexibility (to allow a wider turn), and most importantly, the height of the building are adjusted such that the stunt becomes theoretically possible (although obviously still not plausible). I'm sure any building that fits the description "skyscraper" is hopelessly out of this range, but a building that's just a few dozen meters tall might work (and seriously, does that make the stunt any less awesome??)

If you jumped off a skyscraper, then quite apart from problems catching the pole without instantly getting all your fingers knocked right off your hands (which is what I think would happen, possibly with the pole itself breaking off the wall at the same time), there's also the problem that even if you were able to, by some sort of magic, start flying straight back up at 120 mph (your terminal velocity in freefall) from halfway, gravity and drag would stop you within 100 m. So if the skyscraper is any taller than 200 m (which isn't very tall for a skyscraper) then it just won't work, no matter how strong and flexible the flagpole is and how much of a superhero you are (short of being able to fly, of course).

(@ThatPITA - You lose even more height due to drag than due to the flagpole maneuver, which is why the question, quite sensibly, says "you're falling from a height above the tallest building".)

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Re: What-If 0133: "Flagpole"

Postby Whizbang » Wed Mar 18, 2015 1:53 pm UTC

What if we add more arms?

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Re: What-If 0133: "Flagpole"

Postby speising » Wed Mar 18, 2015 2:52 pm UTC

this treatise fails to include the flexibility of the flag pole. a very flexible pole could cushion the shock to the arms, possibly to bearable levels.

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Re: What-If 0133: "Flagpole"

Postby Neil_Boekend » Wed Mar 18, 2015 3:02 pm UTC

Only if the flexibility of the flagpole allows him to decelerate at 1/10th of the speed. That would mean in approximately 10 meters. I suspect that the flagpole is not able to do that.
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Re: What-If 0133: "Flagpole"

Postby SDK » Wed Mar 18, 2015 3:40 pm UTC

Wiz wrote:I'm a bit disappointed this "What If" didn't end with a scenario a la #43 (Train Loop) where the jumper's arm strength, the pole's strength & length & flexibility (to allow a wider turn), and most importantly, the height of the building are adjusted such that the stunt becomes theoretically possible (although obviously still not plausible). I'm sure any building that fits the description "skyscraper" is hopelessly out of this range, but a building that's just a few dozen meters tall might work (and seriously, does that make the stunt any less awesome??)

I too want to know what height to attempt this from. You were going to do it yourself, right?
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Re: What-If 0133: "Flagpole"

Postby Quercus » Wed Mar 18, 2015 4:09 pm UTC

...m... wrote:but i think a much better-suited example for this sort of maneuver would be an extreme brachiating primate species, like a gibbon, to observe the median and maximum vertical drop achieved in nature...


Brachiation is a wonderful word, thanks for introducing me to it. :D

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Re: What-If 0133: "Flagpole"

Postby Tyndmyr » Wed Mar 18, 2015 4:27 pm UTC

Best way to solve this scenario without losing arms/splattering/etc is to focus in on "tallest building in your town", and live somewhere with squat buildings.

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Re: What-If 0133: "Flagpole"

Postby Pfhorrest » Wed Mar 18, 2015 4:50 pm UTC

One big caveat that strikes me: you're falling from "a height" above the tallest building in your town, and "partway" down is the flagpole. This could strictly mean you're falling from a foot above the building, and another foot down the side of the building is the flagpole, so you only need to fall two feet before reaching the flagpole.

This occurred to me because of Tyndmyr's comment above, which made me realize the tallest building in my town is the post office tower at about three stories tall, and it does in fact have a flagpole... very near the top of it. I'd imagine if a gymnast were to stand on another person's shoulders on the roof of the tower and jump to grab the flagpole, she could probably do so successfully, until the flagpole broke off the side of the building, or (if it didn't) she ended up in the air between the flagpole and the edge of the roof of the tower and started falling two-and-a-half stories to her, if not death, probably pretty serious injury.
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Re: What-If 0133: "Flagpole"

Postby rmsgrey » Wed Mar 18, 2015 5:02 pm UTC

Yeah, jumping onto a flagpole from that sticks out of the top of the building and bouncing back seems rather more survivable than one only 10 feet above the pavement - and is not excluded by the question...

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Re: What-If 0133: "Flagpole"

Postby mathmannix » Wed Mar 18, 2015 5:22 pm UTC

Tyndmyr wrote:Best way to solve this scenario without losing arms/splattering/etc is to focus in on "tallest building in your town", and live somewhere with squat buildings.

True. That was my first thought when I got to the point where RM said
The "tallest building in town" here in Boston is the 240-meter-tall Hancock Tower

I assumed he was then going to mention that many towns (possibly most; especially in the U.S. if you consider only "towns" and not "cities") have a tallest building of around 3 stories.
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Re: What-If 0133: "Flagpole"

Postby senor_cardgage » Wed Mar 18, 2015 5:36 pm UTC

What if it's one of those cartoon flagpoles that bends so much that it flings you back upwards, so you don't even have to swing around?

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Re: What-If 0133: "Flagpole"

Postby speising » Wed Mar 18, 2015 5:38 pm UTC

senor_cardgage wrote:What if it's one of those cartoon flagpoles that bends so much that it flings you back upwards, so you don't even have to swing around?

then it depends on whether you're the coyote or the roadrunner.

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Re: What-If 0133: "Flagpole"

Postby Oneknown » Wed Mar 18, 2015 6:11 pm UTC

So... I was curious how far you could fall and pull off this stunt given the variables used here.

First, I converted mi/h to km/h, because metric system! Then I reduced the velocity until the force was less than 10 kN.[1]

Then using this freefall calculator[2] I found that a freefall time of 1.840 seconds yields a velocity of 64.96 km/h, which is a fall from 16.60 meters.

So you can jump off a skyscraper and pull this trick off. You just need to make sure the flagpole is no further than 16 meters down.

[1] Wolfram alpha dot com/input/?i=100+lbs+*+%2865+kmph%29%5E2+%2F+%281.5+meters%29
[2] keisan dot casio dot com/exec/system/1224835316

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Re: What-If 0133: "Flagpole"

Postby sevenperforce » Wed Mar 18, 2015 8:44 pm UTC

speising wrote:
senor_cardgage wrote:What if it's one of those cartoon flagpoles that bends so much that it flings you back upwards, so you don't even have to swing around?

then it depends on whether you're the coyote or the roadrunner.

The roadrunner gets flung gracefully back up to the roof; the coyote gets splatted into the side of the building.

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Re: What-If 0133: "Flagpole"

Postby Mikeski » Wed Mar 18, 2015 11:10 pm UTC

sevenperforce wrote:
speising wrote:
senor_cardgage wrote:What if it's one of those cartoon flagpoles that bends so much that it flings you back upwards, so you don't even have to swing around?

then it depends on whether you're the coyote or the roadrunner.

The roadrunner gets flung gracefully back up to the roof; the coyote gets splatted into the side of the building.

Even Especially if it's the same exact flagpole.

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Re: What-If 0133: "Flagpole"

Postby CharlieP » Thu Mar 19, 2015 11:18 am UTC

Oneknown wrote:First, I converted mi/h to km/h, because metric system!


Very laudable, but wouldn't m/s be more useful in almost every way?
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Re: What-If 0133: "Flagpole"

Postby quantum7 » Thu Mar 19, 2015 12:08 pm UTC

Neil_Boekend wrote:Only if the flexibility of the flagpole allows him to decelerate at 1/10th of the speed. That would mean in approximately 10 meters. I suspect that the flagpole is not able to do that.


I pictured a looney-tunes type senario where our hero grabs the tip of the pole, which bends like rubber, cushioning the fall before sling-shotting him to the sky. This is better modelled by a spring rather than the equation for rigid rotation you cite.

Given [imath]v_0 = 45 m/s[/imath] (100 mph), [imath]m = 45 kg[/imath] and [imath]F<10 kN[/imath], I calculate that the flagpole would have to bend at least [imath]m*v_0^2 / F = 9 m[/imath] in order to keep the hero's arms attached. That's a lot, but it's not too unreasonable given the error in other parameters such as the height. Note that this would require the flagpole to have a spring constant of [imath]k = (F/v_0)^2 / m = 1000 N/m[/imath]. This seems achievable for a flagpole (I found an estimate for car suspension springs with k=25000 N/m).

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Re: What-If 0133: "Flagpole"

Postby JeffR23 » Thu Mar 19, 2015 6:23 pm UTC

I'm also more interested in the other half of the question, so recasting: is it actually possible to launch someone (with, say, a human cannonball, a catapault or trebuchet, or an old-school seesaw-and-dropped weight system) close to but not quite straight up near a tall building such that they're at nearly zero vertical velocity and a very small horizontal one when they land on the rooftop such that they can simply start walking forward without missing a step? Or are the tolerances for error so low that you'd almost always end up missing the mark or winding up with too much rotation or hitting the wall instead...

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Re: What-If 0133: "Flagpole"

Postby Neil_Boekend » Thu Mar 19, 2015 6:41 pm UTC

quantum7
How you decelerate doesn't matter. To decelerate in x seconds by y m/s you need to apply certain force.
Unless you're being caught by Superman apparently.
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Re: What-If 0133: "Flagpole"

Postby Izawwlgood » Thu Mar 19, 2015 6:44 pm UTC

As someone who is healing from surgery to repair a torn bicep, I appreciate this comic.
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Re: What-If 0133: "Flagpole"

Postby sevenperforce » Thu Mar 19, 2015 7:13 pm UTC

JeffR23 wrote:I'm also more interested in the other half of the question, so recasting: is it actually possible to launch someone (with, say, a human cannonball, a catapault or trebuchet, or an old-school seesaw-and-dropped weight system) close to but not quite straight up near a tall building such that they're at nearly zero vertical velocity and a very small horizontal one when they land on the rooftop such that they can simply start walking forward without missing a step? Or are the tolerances for error so low that you'd almost always end up missing the mark or winding up with too much rotation or hitting the wall instead...

Well, to get over the roof without hitting it, they'll need to have a nice little parabola over the top. You don't want to be moving forward faster than a fast walking pace, or you'll hit the ground sprinting. The highest possible walking speed is around 2.5 m/s, so your horizontal speed needs to be less than that.

But it's very difficult to safely descend stairs at a pitch steeper than 45 degrees. In other words, you don't want to be moving down when you land at a greater speed than your overall forward velocity. So, in order to limit your downward speed to less than 2.5 m/s, you need to drop from less than 0.32 meters per kinematic equations.

over the roof.png
over the roof.png (2.38 KiB) Viewed 8312 times


That's a pretty small margin for error. Though it will be easier to pull off on a small building than on a large building.

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Re: What-If 0133: "Flagpole"

Postby Whizbang » Thu Mar 19, 2015 7:14 pm UTC

Neil_Boekend wrote:quantum7
How you decelerate doesn't matter. To decelerate in x seconds by y m/s you need to apply certain force.
Unless you're being caught by Superman apparently.


Evidently Superman has psychokenetic powers that he uses unconsciously to blunt the effects of his strength (I dunno, ask Second Talon), so I can only assume this also is used when he catches people to, somehow, catch them without breaking them.

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Re: What-If 0133: "Flagpole"

Postby Neil_Boekend » Thu Mar 19, 2015 7:21 pm UTC

I just tend to assume physics takes a step back when comics and movies are concerned. It allows for pleasant surprises every once in a while.
Especially when I see it, assume it's bull dung and then learn its actually physically plausible. See the movie sunshine.
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Re: What-If 0133: "Flagpole"

Postby sevenperforce » Thu Mar 19, 2015 7:54 pm UTC

Pyure wrote:I'm curious, what would happen if you were falling from some monstrous height and saw a vertical flagpole nearby? Could you grasp that lightly enough that you could arrest your speed significantly?

I imagine you'd just end up bouncing off it despite your best efforts.

This was, until I re-read the initial question more closely, my initial assumption about the question. Like, if you jumped off the top of the tallest building in town and saw a bare flagpole on the ground, could you grip it and slide down in time to stop before splatting?

Imagining that you were on the right trajectory that you could get your arms and legs around it and basically hug it tightly all the way down, what would the limiting factor be? Hug strength? Frictional heating?

Oneknown wrote:So... I was curious how far you could fall and pull off this stunt given the variables used here.

First, I converted mi/h to km/h, because metric system! Then I reduced the velocity until the force was less than 10 kN.[1]

Then using this freefall calculator[2] I found that a freefall time of 1.840 seconds yields a velocity of 64.96 km/h, which is a fall from 16.60 meters.

So you can jump off a skyscraper and pull this trick off. You just need to make sure the flagpole is no further than 16 meters down.

[1] Wolfram alpha dot com/input/?i=100+lbs+*+%2865+kmph%29%5E2+%2F+%281.5+meters%29
[2] keisan dot casio dot com/exec/system/1224835316

The equation Randal cites in superscript [4] is incorrectly stated; the force F is actually given by F = m*ac, where m is Rex's mass. ac is centripetal acceleration and is given by ac = v2/r. We let r = 2 meters to be generous, and say Rex is a smallish fellow despite his cartoonishly long arms, with a mass of only 65 kg.

In this case, with a maximum force of 10 kN, we get a maximum allowable falling speed of 17.5 m/s, which comes out at 63 km/hr or just under 40 mph, and yes, that's a fall of roughly 16 meters.

So Rex can possibly manage the gymnastically-challenging swing as long as the flagpole is no more than 5 stories down. Which will be halfway if the building is 10 stories high, which is actually fairly respectable.
Last edited by sevenperforce on Thu Mar 19, 2015 8:02 pm UTC, edited 2 times in total.

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Re: What-If 0133: "Flagpole"

Postby Flumble » Thu Mar 19, 2015 7:57 pm UTC

Neil_Boekend wrote:quantum7
How you decelerate doesn't matter. To decelerate in x seconds by y m/s you need to apply certain force.
Unless you're being caught by Superman apparently.

The "super" is for "(supermassive) black holes at my command". (either classical black holes or something with quantum gravity) He doesn't so much "fly" as he bends spacetime to make him fall in the direction he points his hands. It's an elegant explanation for why people survive being caught by him. This is now my headcannon. (same goes for The Matrix, although "it's a computer program" covers it, too)

sevenperforce wrote:Imagining that you were on the right trajectory that you could get your arms and legs around it and basically hug it tightly all the way down, what would the limiting factor be? Hug strength? Frictional heating?

If the person can feel pain, the frictional heating wins, I believe.

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Re: What-If 0133: "Flagpole"

Postby rmsgrey » Thu Mar 19, 2015 8:43 pm UTC

Flumble wrote:
Neil_Boekend wrote:quantum7
How you decelerate doesn't matter. To decelerate in x seconds by y m/s you need to apply certain force.
Unless you're being caught by Superman apparently.

The "super" is for "(supermassive) black holes at my command". (either classical black holes or something with quantum gravity) He doesn't so much "fly" as he bends spacetime to make him fall in the direction he points his hands. It's an elegant explanation for why people survive being caught by him. This is now my headcannon. (same goes for The Matrix, although "it's a computer program" covers it, too)


Canonically, Superman has (or had ten years ago - there have been enough retcons and continuity resets over the last decade that it might have drifted out of continuity again while I've not been following) a form of "tactile telekinesis" - meaning when he catches a falling body, rather than trisecting her, he causes her entire body to accelerate as a whole rather than applying the force through her body...

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Re: What-If 0133: "Flagpole"

Postby speising » Thu Mar 19, 2015 8:54 pm UTC

note that a magic like that is also required to do things like carrying the statue of liberty, instead of just scooping two handfulls of copper out of it.


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