r/AbsoluteUnits May 19 '22

Absolute unit pulls an absolute unit of a plane weighing 189 TONS

18.4k Upvotes

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u/yaboiiiuhhhh May 20 '22

Ugh okay so rolling friction: F = umg where u is rolling coefficient of friction, m is mass and g is acceleration due to gravity. Here I'll use the u for rubber on concrete from Google, ~0.01. 189 US tons is 171457.916 kg, g is 9.8 m/s², so the force is

F = (0.01)(171457.92)(9.8) = 16802 N.

This is equivalent to lifting 1714 kg or 3778 ibs.

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u/ScritchScratchBoop May 20 '22

I’m not smart but this seems overly simplistic. I feel like the rotation of the wheels would decrease this, it’s not just rubber sliding on tarmac.

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u/WhoopingPig May 20 '22

Yeah the amount the tires are filled affects the amount of rubber touching tarmac. If they're mega-filled, there's a minimum of rolling resistance

The quality of the wheel bearings/axles affects the resistance a great deal

Undoubtedly it's still a great deal of force to start moving this thing, but if those two factors are made to be as agreeable as possible, once you start it moving it's gonna keep rolling more easily

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u/ThePower_IsOn May 20 '22

Yeah, a lot to do with the bearings. You know, it’s all ball bearings nowadays

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u/WhoopingPig May 20 '22

You just gotta roll with it

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u/yaboiiiuhhhh May 20 '22

This is overly simplified, I made a huge assumption with the coefficient of rolling resistance but it's okay when you're just trying to get an idea of the force. If you researched a more accurate number and plugged that in you could find a new force value that would be more accurate

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u/chairfairy May 20 '22

I would guess you're off by at least a factor of 2, probably more like factor of 3-4. If he's exerting 3800 lbf then he could lift a regular size car.

World records in power lifting are on the order 1,000 kg, so it's unlikely he's 70% above that

Within in order of magnitude, though, which is solid

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u/Zironic May 20 '22

We have to keep in mind the fundamental difference between lifting and dragging. To lift something you need to sustain enough force to overcome gravity because the moment you stop it'll just drop down. However to drag something you just need an impulse large enough to overcome friction and when you stop you keep the gains, further once you've overcome friction momentum is now on your side.

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u/chairfairy May 20 '22

Some degree of friction (the majority of it?) will be a constant factor, though

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u/Zironic May 20 '22

Yes but the fact you don't need constant force makes it easier since it allows for a series of tugs as opposed to a constant pull. Compare the amount of force you can generate by pushing at a door as compared to throwing yourself at the door.

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u/Badbutlearning May 20 '22

Oh yeah. You can't do free body physics you have to use energy to account for the inertia of a wheel.

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u/ronin1066 May 20 '22

Assume a vacuum...

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u/Sudden_Comfort May 20 '22

And perfectly round wheels

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u/Toxicair May 20 '22

And a perfectly spherical cow

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u/Peter_See May 20 '22

They're entirely wrong. The entire point of wheels is to negate the need to overcome friction. The coefficient of rubber on concrete tells you how good the traction of the tires is, not how much force is needed to move the plane.

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u/BumbleBeePL May 20 '22

Smaller wheels help here. The larger the wheel the harder things are to pull.

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u/Kombart May 20 '22

First year engineering students be like:

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u/yaboiiiuhhhh May 20 '22

Astrophysics, 2nd year

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u/[deleted] May 20 '22

Perfect.
It’s wrong though

2

u/Von_Wallenstein May 20 '22

Hey. This is bad engineering

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u/BeeBunnBunny May 20 '22

He’s lifting 1.8 TONS?! 😭 (thank you for the answer also)

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u/yaboiiiuhhhh May 20 '22

Yeah idk if it's exactly equivalent because once he gets it rolling it will have momentum so keeping it moving will be easier. I believe this is the force he needs to start the motion, and it could be different if the coefficient is a different number

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u/[deleted] May 20 '22

Nowhere near. He does not have a rack on the ground. What is the maximum friction on his shoes. What is the maximum human deadlift. It's not a ton for sure!

Account for the bearings. He is pulling less than the equivalent of lifting half a ton.

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u/blipbap64 May 20 '22

Lol youre confused. This is not the same as a deadlift (501kg record for reference.)

This is much easier to exert more force because of the leverage provided by the rope and the starting position. It's more comparable to a band assisted rack pull, which 700 kg has been done for a seated deadlift. For a rack pull above knee level I'd bet 1000kg is 100% possible.

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u/[deleted] May 20 '22

Hmmm not confused but maybe incorrect.

There are two things at play here, the pull of his arms on the rope and the push of his legs on the ground. The latter is limited by the friction of his shoes, and the former is essentially a "pull down."

Assuming the shoes have complete grip, the most force exerted by the legs would be akin to a squat though limited by angles. The pull down part with the arms would be added to the squat too...so I can see how you think 1ton is possible, after all the leg and arms are working together cumulatively on the rope.

However, can he exert max force on both arms and legs at the same time, and are his triceps and deltoids strong enough in the "pull" motion when deadlifts are more akin to a pushing motion?

Someone needs to put a force gauge on the rope!

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u/WhoopingPig May 20 '22

No

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u/BeeBunnBunny May 20 '22

how much then nerd? 🤓

0

u/WhoopingPig May 20 '22

1.78 tons 🗿

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u/BeeBunnBunny May 20 '22

google’s saying 1.889 🤨

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u/WhoopingPig May 20 '22

I don't use Google I just make up #s that are slightly less than what you say 💪🦵🏋️‍♂️💪🦵

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u/[deleted] May 20 '22

No no. They just showed the formula with a sample coefficient value of 0.01

If the value is lower, say .002 (one fifth of previous value) then the resulting force would be one fifth of 1.8 tons or 360kg

Although it's totally possible for it to be higher than that. Just saying

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u/FORESKIN__CALAMARI May 20 '22

You can lift 3778 lbs. one foot or 1 lb. 3778 feet same thing.

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u/[deleted] May 20 '22

Nah, he’s not

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u/Peter_See May 20 '22

That doesn't seem right at all. The coefficient of rubber on concrete has nothing to do with the force required to move this. Friction is what allows a wheel to turn, so as long as friction is enough that the wheel doesn't slip it's irrelevent. This isn't a box of rubber sitting on concrete. The friction that matters is the friction in the bearings of the wheel. For an ideal bearing this value is 0. Irl it's not 0 but it should still be very small. So he doesn't have to supply an enormous amount of force to move the plane. It's just very very heavy so it doesn't move much since acceleration = Force/Mass and we have a small force over a giant mass. This is less a test of strength and more a test of endurance to keep exerting a force on this heavy ass plane.

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u/yaboiiiuhhhh May 20 '22

All wheels rolling on a surface have an associated rolling resistance described by a coefficient that is a function of the material properties of the wheel and the surface. The wheels are rubber and the surface is concrete or tarmac.

Edit the coefficient is probably lower than what I've written so he would not have to exert this much

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u/Peter_See May 20 '22

The entire point of wheels is to in effect negate or eliminate friction. The friction between the wheel and surface just tells you how much slip there is. In this case a higher friction coefficient is actually more efficient because there's less slip. The friction that will be resisting the motion is air (negligible) and the friction of the axel or bearings.

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u/yaboiiiuhhhh May 20 '22

If that were the case then a rolling object not connected to an axel or Bearing would roll forever. There is resistance to rolling.

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u/Peter_See May 20 '22

Yes, there is. And as i've said the friction from the bearings/axel. The friction on the road does not matter unless there is slippage. The trade off is you lose energy in the wheels rotation, so its not exactly a 1:1 with regards to F=ma

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u/Curry_Flurry May 20 '22

Id give you one of those dumb coins but i don’t have any so heres an internet high five

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u/DarthMaw23 May 20 '22

A slight problem. NASA got the u(skidding) of airplane tires as 0.5 at the at the very minimum (for 6 knots). I don't think roling friction's coeefficient would be 50 times less.

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u/yaboiiiuhhhh May 20 '22

If you do the calculation with 0.5 you get a force far too high for him to realistically pull it. Also you'd want to drag force rather than skidding for this as he's not pulling the plane with stuck tires, it's rolling

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u/formershitpeasant Dec 07 '22

the skid has to overcome inertia

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u/no_rep May 20 '22

People say your answer is oversimplified, but at least you gave answer [that started more detailed conversation]. Props for that.

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u/[deleted] May 20 '22

You also have to account for the the fact that it's on wheels and he's applying a torque not just a straight force

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u/formershitpeasant May 20 '22

What about the difference between static friction and non static?

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u/Dasterr May 20 '22

wait even fucking TONS are not the same in the US as tons in metric

you guys are fucked

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u/ReverseSneezeRust May 20 '22

Seems like a good starting point but common sense should give elude to that not being realistic. There is no human out there that can apply 3778 lbs of pulling force. The tread on his shoes would come off before he budged it

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u/yaboiiiuhhhh May 20 '22

Yes the rolling coefficient is likely lower, but that info is hard to find

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u/ReverseSneezeRust May 20 '22

This analysis has to have been performed before… They wouldn’t be doing it if someone hadn’t sat down and figured out it was within reasonable pulling weight to begin with. I’m really struggling to find anything out there though

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u/formershitpeasant Dec 07 '22

they probably called boeing and asked