Here is the graphic on teamwork http://i.imgur.com/1Hp6r.jpg
My take is that the two folks will not be able to hold the beam with one person hanging on the side.
So is this picture humanly possible assuming all three folks in the image are of equal weight and strength ?
Thanks
Theoretically, in the perfect world of a physics lecture hall, yes. If you imagine those to be three weights, you could have two of them on a counter and one hanging off the edge and it would balance. However, put a human on the end and as soon as he moves, at all, his momentum is going to add weight to his end of the lever in a way that the rear person can’t counter.
That is, if he moves his feet up, then back down, or if his legs drop as he goes off the edge, there’s going to be a downward force that is more than equals more than his weight. However, then person at the back can only pull down by the amount that they weigh, they can’t add more weight.
I’m not sure if that makes sense, but it’s how I’m reading it.
ETA and looking at how it’s pictured, it wouldn’t work. First guy goes over the gap and goes limp while rear guy is still walking light on his feet. For it to work, the first guy would have to stay rigid as he goes over the gap and the rear guy would really have to have a good grip on the bar and probably keep his feet firmly planted on the ground. Any bounce in his step (or any up and down motion of his shoulder) and it’s going to teeter over.
I can see a way to make it work, but without practice, confidence and trust I think that first guy is going to fall in the hole.
Assuming that they are of equal weight and evenly spaced, the person in the middle is going to be bearing the weight of all three of them when one of the end people is over the gap. The person on the other end won’t be able to support the weight any, and will actually need to hang from the beam with all their weight to keep it balanced on the person in the center.
But, as I said this is one of those ‘perfect world’ things. If the guy over the gap moves at all, the downward momentum will add to his weight he’ll that end of the lever will weigh more than back end and it’ll tip. If I got this on a physics test, I’d say it would work. IRL, I wouldn’t try it.
Think about trying to pull down on something really heavy. You hang from it and it doesn’t move so you start jerking your body around. Pulling yourself up and dropping back down and eventually it goes. Same idea, but since you only need to be just a little more than your body weight to work, since it’s perfectly balanced, it’s not going to take move movement at all. A good downdraft might do it.
Yes, when the first person is over the gap and hanging on the beam, the middle person is a fulcrum supporting the weight of all three people and the beam. The back person is hanging on the beam to counterweight the front.
Agreed it’d work in a perfect world. Even a great chance it’d work in the real world.
At all times there’s always an over-balance of weight from the people on the side of either platform (except when the girder is crossing it’s exact middle, when it’s evenly balanced on the front and back people), to the people’s advantage.
You’d just have to make sure there’s always a time at least 2 people have a foot/feet on the ground.
Assuming that the beam itself isn’t of an overwhelming weight, the two on the ends might be able to support the middle person, but the middle person couldn’t support the other two. See the fulcrum comments above.
If the people on the front and back could jump the gap, it would be best for them to just let go, jump and then bear the weight again. That way the other two only have to contend with an extra third of the weight of the beam. Well, more for the middle person and less for the back person, but you get the idea.
IIRC, steel girders weigh between 15 and 20 pounds per foot. That one is fairly slender, and about 20 feet long, so I’d put it in the realm of 300 pounds. Just moving each person’s beam load from 100 to 150 pounds is a lot. Add half the human as well, (supposing the simplest possible misconception of the physics) would mean each was carrying and balancing 230 to 260 pounds while one was on the gap.
ETA: They should put the beam down, walk over it across the gap, then slide it through and pick it up again.
The weight/density of that beam certainly is a crucial variable. For all we know, it’s a 2x4.
Assuming it can physically support them, the weight is evenly distributed across it’s length and the two end people are strong enough to hold half of it (more or less) plus the weight of the hanging person, it shouldn’t make a difference if it’s a 5 pound carbon fiber rod, a 10 pound wood 2x4 or a 200# steel I-Beam.
But, yeah, if we really want to get into a real world analysis of this, you should make sure it’s not just going to snap in half, I mean, that middle person might get a splinter.
If the beam weighs nothing, then when the third (or first) person is hanging, the person in the middle (assuming every one of the people is of the same weight) has to support double his/her weight.
If the beam weights 200lb, then that person in the middle has to support double his/her weight plus the 200lb.
That’s quite a big difference. Can an average person support double his weight while walking even a short distance? I am not sure.
Apart from this, the balance when the third (or first) person is hanging over the gap is not stable, so I would presume the first (or third) person in the pic would have to make sure to somehow pull his part down as the other side’s person goes over the gap.
The OP says to assume all three folks are of equal weight and strength. Let’s also assume the beam weighs the same as one person, X. So the total weight = 4X. Assume that each person is strong enough to lift 5X.
The three line up, and the two on the ends lift their feet
The middle person, carrying the entire load, walks toward the gap until the front person is past the gap
Two end people lower their feet, middle person lifts his feet, and group walks forward until middle person is past gap
Middle person feet down, end people feet up, forward until back person is across gap
It might not be humanly possible, but it is physically possible.
Actually, the maximum required strength would only be 3X.
I think a key factor would be moving the beam’s fulcrum point.
Let’s say the gap is two meters and the beam is six meters long. And assume all three people weigh the same and can support the weight.
So Al’s walking in front, Barb is two meters behind him, and Carl is at the end.
Al gets to the gap, hangs on to the beam and steps off. He should be okay because he’s two meters from the fulcrum (Barb) while Carl is four meters from the fulcrum. So Carl is exerting more downward force than Al is.
Barb then walks forward until she’s at the edge of the gap. She then stops in place and let’s the beam slide along her shoulder. Carl continues walking forward.
Al reaches the other side of the gap while Carl still has the majority of the beam on his side of Barb. Al is now supporting his own weight and walks forward. Barb stops letting the beam slide on her shoulder and is carried out over the gap.
When Barb gets past the gap, she stops at the edge and again lets the beam slide on her shoulder. Al and Carl keep walking. By the time Carl reaches the edge, there should be two meters between him and the fulcrum (Barb) and four meters between the fulcrum and Al. So Al is now exerting more downward force than Carl. So Carl can hang on to the beam and be carried across. Barb and Al walk forward until Carl reaches the other side of the gap.
It also depend on their speed. If they were [del]walking[/del] running at 100 mph, they’d barely need to do any balancing or footwork.
Seems like the kind of thing that would be easily testable, and then be put up on Youtube.
I’m assuming this is a joke but it actually illustrates a common fallacy. It’s Elmer Fudd physics: the idea that you travel level for a brief interval before you start falling (and then generally fall straight down).
The reality is that gravity effects you instantaneously. There’s no such thing as level flight unless you’re producing lift.
No. Unless person in centre is a weight lifter with super strength, the answer is NO.
The person in the middle, when one end guy is over the gap is holding up
the beam and BOTH men.
Due to imperfection, they may have to hold more than that, but I am pretty sure the theoretical minimum weight on the person in middle when one end guy is over the gap, is too much for an ordinary person… If the two end people are horse jockeys and the person in middle is super strong, maybe…But not if they are three equal people.
The reason is … The person over the gap is hanging, and the beam rotates around the person in middle. Then the person at the other end, is not able to carry his own weight, he is hanging off the beam, and so person in middle is carrying both end people, and beam.
Yeh, it was a joke (hence smilie).
Although, at some exceedingly fast but unrealistic speed, they should be able to fly across the gap.
All things being equal, when the first guy is over the gap, couldn’t the guy in the rear lower his center of gravity by crouching, thereby enforcing some leverage?
While I hadn’t considered that, that’s exactly that kind of stuff that gets ignored, and is meant to be ignored when we say “in a perfect world” in physics class. The same way you ignore air resistance, friction, heat and just about every other force that you’re not directly testing.
The middle guy might actually be able to support 800 pounds on his shoulder, but he went out drinking last night and has a migraine and his muscles are really shaky, so it’s not going to work tonight.
Imagine it’s just three big wheels, make them as heavy and strong as you want or three people sized pillars with wheels at the bottom that can be pushed across the gap. The system is strong enough that it won’t collapse. Would it work then? Assuming that’s what’s really being tested, I vote yes.
