# Newton's First Law to explain Washing Machine Spin Cycle

• thomas_shvekher
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.f

#### thomas_shvekher

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.

A body remains at rest, or in motion at a constant speed in a straight line, unless acted upon by a force.

Lnewqban
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?

Lnewqban
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?

russ_watters and thomas_shvekher
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?

russ_watters and Lnewqban
It seems that wet dogs understand how this works. What do you see the water do?

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

Lnewqban
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.

thomas_shvekher
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!

Lnewqban
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##

...The water would still fly off . Thanks!

thomas_shvekher
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.

Lnewqban and jbriggs444
I thought so too

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.

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Lnewqban
Here is a slow-motion demo.

DrClaude, PeroK and thomas_shvekher
Here is a slow-motion demo.

So interesting!

erobz
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.

thomas_shvekher
It is just a picture that Google found for me.
Did Google say what this is supposed to depict? I am curious.

Revised picture regarding rotation direction:

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.

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?

erobz and jbriggs444
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).

Lnewqban and erobz