Newton's First Law to explain Washing Machine Spin Cycle

In summary, the picture depicts an example of Plateau-Rayleigh instability, where the water droplets in a photograph become spiral due to the influence of a external force.
  • #1
thomas_shvekher
10
6
Homework Statement
Use inertia and Newton’s first law to explain how the spin cycle in a washing machine removes
water from clothes.
Relevant Equations
Newton's First Law
I truly am not sure. I assume it is that because everything has inertia, an a tendency to remain in a constant state of motion, when the clothes are quickly spun around they cannot remain in a constant state of motion (of either rest or constant velocity), but the water is "pushed"/spun out of the clothing "with the goal of being in an equilibrium", although I do not think this is correct.
 
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  • #2
A body remains at rest, or in motion at a constant speed in a straight line, unless acted upon by a force.
 
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  • #3
Could this mean that water is not acted upon by an external force, meaning it travels our of the clothing in a straight line (into the holes of the washer), while the clothing ocntinues to spin aound as an external force acts upon them?
 
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  • #4
The question is why don't your clothes leave the washing machine and why you don't end up with a drum full of water?
 
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  • #5
So the idea behind the question is that Newton's First Law states that the wet clothing will try to move in a straight line, and the holes on the drum will allow the water to espace, but not the clothes?
 
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  • #6
It seems that wet dogs understand how this works. What do you see the water do?

 
  • #7
kuruman said:
It seems that wet dogs understand how this works. What do you see the water do?


It looks like the water "flies" off in a straight line
 
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  • #8
The spinning drum physically forces the clothes to deviate from the natural straight line that they would follow, according to the Newton's enunciate.
That drum can induce a centripetal acceleration to the solids, but the liquid would scape that effect.
The perforated walls of the drum are unable to "grab and drag" the water into a circular movement.
 
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  • #9
Lnewqban said:
The spinning drum physically forces the clothes to deviate from the natural straight line that they would follow, according to the Newton's enunciate.
That drum can induce a centripetal acceleration to the solids, but the liquid would scape that effect.
The perforated walls of the drum are unable to "grab and drag" the water into a circular movement.
Thank you so much!
 
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  • #10
thomas_shvekher said:
It looks like the water "flies" off in a straight line
And if you put a put a soaked jacket on the dog, the water would still fly off, no?
And if you put the soaked jacket in a washing machine's spin cycle instead of on the dog, then ##~\dots##
 
  • #11
...The water would still fly off 😂. Thanks!
 
  • #12
Pump-operation.png
 
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  • #13
Lnewqban said:
How was this picture made and what is it of? It seems to me that the likeness of a single leaking bucket was cut and pasted in a symmetric pattern with an arrow added to suggest clockwise rotation. If that is the case, I think that the stuff coming out should be following not leading the bucket.
 
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  • #14
I thought so too
 
  • #15
kuruman said:
How was this picture made and what is it of? It seems to me that the likeness of a single leaking bucket was cut and pasted in a symmetric pattern with an arrow added to suggest clockwise rotation. If that is the case, I think that the stuff coming out should be following not leading the bucket.
The drawing is confusing. I think it is intended to depict the forward progress of a particular bit of each of the four water sprays over a time lapse. However, the buckets from which those four sprays emerged are depicted as a frozen snap shot from the time that the bit was sprayed.

A more faithful depiction of that concept might have used a single droplet at the bottom of each bucket and dotted lines (perhaps decorated with series of equally spaced dotted droplets) depicting the future paths of each of those four droplets.

Each of the sprays would properly have been a straight line leading trajectory nearly tangent to the circle of buckets if depicted in this manner. It would not have the curve that is improperly shown in the drawing from #12. The departure from an exact tangent would be due to a non-negligible exit velocity from the spout at the bottom of each bucket.A set of four concentric trailing spiral curves broken into water droplets due to Plateau-Rayleigh instability would be characteristic of an actual photograph.
 
Last edited:
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  • #16
Here is a slow-motion demo.

 
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  • #17
erobz said:
Here is a slow-motion demo.


So interesting!
 
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  • #18
kuruman said:
How was this picture made and what is it of? It seems to me that the likeness of a single leaking bucket was cut and pasted in a symmetric pattern with an arrow added to suggest clockwise rotation. If that is the case, I think that the stuff coming out should be following not leading the bucket.
It is just a picture that Google found for me.
Thank you for the correction, the rotation arrow has the wrong direction.
I will try to fix it later.
 
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  • #19
Lnewqban said:
It is just a picture that Google found for me.
Did Google say what this is supposed to depict? I am curious.
 
  • #21
Revised picture regarding rotation direction:

Pump-operation.jpg
 
  • #22
Lnewqban said:
Revised picture regarding rotation direction:

View attachment 324526
Now we have the question: What do those arrows at the outer ends of the spray streams denote?

What they do not correctly denote is the flow direction.
 
  • #23
jbriggs444 said:
Now we have the question: What do those arrows at the outer ends of the spray streams denote?

What they do not correctly denote is the flow direction.
Agree.
What about revision 2?

Pump-operation.jpg
 
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  • #24
Lnewqban said:
Agree.
What about revision 2?

View attachment 324541
Plausible. A droplet's direction should be a combination of radial (from the ejection velocity) and tangential (from the bucket velocity at the time of ejection).
 
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FAQ: Newton's First Law to explain Washing Machine Spin Cycle

What is Newton's First Law and how does it relate to a washing machine's spin cycle?

Newton's First Law, also known as the Law of Inertia, states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. In the context of a washing machine's spin cycle, this law explains why clothes and water tend to move outward to the drum's edge when the drum spins. The inertia of the clothes and water resists changes in motion, so they continue moving in a straight line, which in a rotating drum, translates to moving outward.

Why do clothes stick to the drum's walls during the spin cycle?

During the spin cycle, the drum rotates at high speeds, creating a centrifugal force that pushes the clothes outward. According to Newton's First Law, the clothes tend to maintain their state of motion. As the drum spins, the clothes' inertia causes them to press against the drum's walls. This force is what keeps them stuck to the drum's circumference.

How does the spin cycle remove water from clothes?

The spin cycle removes water from clothes through the principle of inertia described by Newton's First Law. As the drum spins, the water in the clothes is forced outward due to its inertia. The drum's perforations allow this water to escape, leaving the clothes drier. The centrifugal force generated by the spinning drum effectively pushes the water out of the fabric.

What role does the washing machine's drum speed play in the spin cycle?

The speed of the washing machine's drum is crucial in the spin cycle because it determines the amount of centrifugal force applied to the clothes. Higher speeds generate greater centrifugal force, which, according to Newton's First Law, means a stronger outward push on the clothes and water. This increased force more effectively removes water from the clothes, making the spin cycle more efficient.

Can Newton's First Law explain why heavier clothes take longer to dry in the spin cycle?

Yes, Newton's First Law can help explain this phenomenon. Heavier clothes have more mass, which means they also have more inertia. This greater inertia requires more force to change their motion. During the spin cycle, heavier clothes resist the outward push more than lighter clothes, so it takes longer for the centrifugal force to effectively remove water from them. Consequently, heavier clothes may take longer to dry compared to lighter ones.

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