ELI5: when 2 people lift the same object together; is there a heavy end?
Posted Apr 9, 2016, 11:11 PM UTC
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I have often overheard people complain about getting the heavy end when lifting and moving large objects in a group. Wouldn't both people be holding the same amount of weight off the ground? Is there some mechanism of balance at play that can change this distribution of weight?
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Like I said, not all objects are equally balanced, and not every lifts with the same force.
If you are moving on a incline, one side will be higher than the other at some point and when that happens the center of gravity shifts towards the lower side making it "heavier".
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Take it to extremes and you'll see that it can indeed be out of balance.
Imagine lifting a weight-lifting bar with equal weights on each end. If you're one end and your friend the other, then you'll both have the same weight to lift.
Now take the weights off one end. Which end would you rather lift?
Now - you can get round this, as you rightly suspect, by shifting your point of lifting until the two of you are sharing it equally, but the important thing is this doesn't happen automatically. In the case of the weights bar you'd have to move closer to the heavy end until you're sharing equally again. You can determine the balance point fairly simply, just by lifting at one point until it doesn't tip, then lifting equal distances from that point.
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When two people lift an object they act almost like a teeter-tooter or see-saw... so depending on where the balance point of the object is, it could lean one way more than the other... that will give it a "heavy side".
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This is the bit that I struggled with ; where is the fulcrum point? It's hanging in the air except for the two holding points at each end. If I hold my end up, I thought I become the fulcrum passing equal weight to the other end? So the higher weighted side is effectively falling faster?
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I'm probably oversimplifying but both people need to do their best to get a good grip on the object, squat, then both slowly pick it up so you can carry the load equally. If someone isn't used to heavy lifting, it might feel heavier on their end. Make sure both understand how to properly lift with their legs.
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Almost always, yes.
Until the places where both people are lifting are completely symmetrical with respect to the center of gravity of the object, it will feel heavier to one of them.
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But almost always people do lift symmetrical things symmetrically. Like furniture.
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Maybe close to symmetrical, but not perfectly symmetrical. If one person is an inch closer to the center of gravity, their end will feel a little heavier.
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In my line of work, I carry heavy stuff sometimes. Sure all these armchair carrying experts on reddit tonight are right when they say that some objects have a heavy end. I'll take you to school on some next level carrying stuff. Ready? When you are carrying something on level ground with a buddy, and everything is equal, then you start going up stairs and suddenly the guy on the bottom gets more weight. Get ready to have your mind blown again, the bottom is usually the easier part, that guy gets to stand up straight with a good grip while mr topsides has to bend down and often has a worse angle to hold onto.
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It depends on a few things.
What is the internal weight distribution of the object? There could be more weight concentrated on one side than the other.
Is one person applying more force than the other? This is almost always yes because it's very difficult to have two people apply the same exact force at the same time, but for most people this difference is very small.
For more on this topic research the term center of mass. Enjoy.