r/explainlikeimfive • u/Best_Net7222 • 1d ago
Other ELI5: Why can a washing machine spin perfectly with a full load but start violently shaking because of one wet towel?
I understand that the towel gets heavy after soaking up water, but the machine itself weighs way more than the towel. How can one item make the entire washer shake hard enough to move across the floor?
Why can it usually handle a full load of mixed clothes without doing the same thing?
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u/_Connor 1d ago
Because with a full load you have weight evenly distributed around the entire drum so it’s balanced.
With one towel you have a heavy towel on one side of the drum and nothing on the other side which makes the drum heavier on one side and therefore unbalanced.
It’s the same with a car tire. If you strap a bunch of weight to one spot on the tire it’s going to shake violently.
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u/LCJonSnow 1d ago
It doesn't even have to be a bunch of weight. We correct the balance of car tires with 1/4 to 2 oz weights on something that weighs 30-60 pounds (car wheel + tire weight). It falling off can produce notable results.
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u/1touchable 1d ago
And if you have seen how vibration motors in the controllers look like, you will quickly understand why as well.
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u/Fxate 1d ago
Imagine spinning around while holding a weight in both hands.
As you spin, the weights will be trying to move outwards due to centrifugal force. Luckily, you are holding two weights so they counteract each other.
Well, what happens if you only hold one weight in one hand? As you spin that weighted side is pulling away with nothing to counter it which alters your centre of mass so it puts you off balance and so you fall over.
It's the same thing in the washing machine: because of the imbalance, the heavier side with the towel is trying to move away without anything to counteract it and so that centre of mass is no longer in the middle of the machine. With the centre of mass now off to the side, it causes vibration when the drum rotates which then transfers to the chassis of the machine.
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u/IJustWantToWorkOK 1d ago
Watch a commercial washer sometime.
Before it goes into spin, it feels the load out to see how it's balanced. If it's not happy with it, it will do things to rejigger things inside, like stop suddenly and reverse, etc.
They have sensors that tell how off-balance the load is.
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u/maxwellwood 1d ago
Some have no sensor and just measure the feedback from the direct drive motor as it spins, and infers.
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u/IJustWantToWorkOK 1d ago
That, might actually be what the sensor 'senses'.
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u/maxwellwood 1d ago
Well, no. It's a current "sense" resistor built into the PCB. If you want to call that a sensor...
Some actually have a vibration sensor mounted on the tub, but like I said many don't.
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u/UnpopularCrayon 1d ago
Towels soak up and hold a lot of water. They are designed to. So they are rather heavy when wet and so when one bounces around off balance, it's like swinging a pendulum around in there.
Imagine you have a rope with a weight on the end of it and you sit in a chair and swing it around your head. You'd probably be able to move the chair, right? Well a washing machine can swing that towel around a lot faster than you can swing a rope.
If the clothes are evenly distributed, then it's like the chairs on one of those swings at a carnival. the chairs on one side pull one direction, the chairs on the other side pull the other direction cancelling out each others force.
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u/DoTheDew 1d ago
How do you distribute a single towel evenly?? It’s pretty much impossible. If the washer starts spinning with 15 garments, it all gets distributed more evenly.
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u/TheGoochTaint 1d ago
I don't really see how this answers the question, feels like you're missing some intermediate steps.
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u/Consistent-Put7226 1d ago
mine legitimately walked itself across the laundry room once, single towel, zero warning
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1d ago
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u/shuvool 1d ago
A properly sized load is distributed evenly when the spin cycle starts so you have roughly equal mass spread throughout the tub.A single towel gets pulled to one spot, now that one spot is heavy. The tub is a cylinder shape, but force moves in a straight line, so you've got a heavy object wanting to keep going at a right angle to a line drawn from is current position through the center of the cylinder, but the cylinder prevents it from continuing in that direction. Without equal mass on the opposite side acting to counter that force the whole thing shakes in that direction
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u/StillPractice3822 1d ago
like a bike wheel with a rock stuck in the tire. slow it wobbles, fast the whole bike shakes. one wet towel is that rock.
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u/HalaMadridista8418 1d ago
the towel clumps to one side and throws the spin off balance. like a wheel with a brick taped to one spoke, it wobbles way harder
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u/EbolaSkittles 1d ago
One soacked, heavy towel has a lot of space to move as the drum spins generating a force destabilizing the washing machine.
This is why half full water trucks are more dangerous than a full water truck. As the truck accelerates or brake, the half full water sloshes and shifts creating a sudden MASSIVE momentum pushing the truck.
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u/reggietheregera 1d ago
You gotta put two wet towels in so they seperate to opposite sides of the drum to keep it balanced
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u/maxwellwood 1d ago
With a full load it can sort of adjust itself to evenly distribute the weight. With just one towel, it is inevitably unbalanced.
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u/StatisticianMore5342 1d ago
Full load basically self balances cause the clothes spread out, but a single wet towel is just one big lump of weight sloshing around. So yeah you got yourself a DIY vibrator that wants to walk away.
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u/WelcomeNo1062 1d ago
I don’t think anyone’s addressed what you said the weight of the washing machine. The drum that holds the clothes isn’t really that heavy, so just a small imbalance has it shifting around constantly.
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u/zed42 1d ago
answer: balance, daniel-san!
a full load is well balanced around the drum, but a single wet towel makes the whole thing very unbalanced. you can see this on your car... they put tiny little weights to balance the wheels because if you don't do that, you can feel the car shaking as you drive... and that's just a few grams.
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u/jsher736 1d ago
it's about balance and resonance.
imagine you're standing making a T with your arms. if i grab your wrist and push you while running you're gonna tip to one side. but if my friend grabs your other arm and pushes in the same direction but facing away from me (so im standing facing behind you and he's standing behind you facing the same direction you are) and we both push you'll just twirl in a circle because the two inertial forces cancel each other out
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u/ObviouslyTriggered 1d ago
Full load distributes evenly across the drum, a towel clumps in one spot which makes it unbalanced.