Why are they cylindrical shape and not ball shape. Would that not be better for more random movement of the items inside and therefore be better for washing them?
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You can put more clothes in it if it’s a cylinder. No matter what shape it is, if it spins it takes up a cylinders worth of space, so making it any other shape is just making it smaller than it could be.
The highest centrifugal force (force made by spinning things) is at the edges, with a cilinder there is much more space at the edges than with a ball shape. This means that more clothes get the maximum force at once and more spread out over a large surface where all the water can get out. With a ball shape all of the clothes would kinda bunch up on those other side decreasing surface area covered.
Volume of a cylinder is greater than the volume of a sphere of the same size. The machine would need to be bigger to handle the same load
If we’re talking a front loader, the load doesn’t just tumble from left to right with the rotation of the drum. Notice the shape of the door glass, and how the inside is sloped? The reason for this is to gently, and gradually, roll the load from front to back during the wash cycle. It also helps push the load away from the rubber seal, so items don’t scuff it up or get caught in there.
In a top loader, the oscillation of the agitator does indeed drag the clothes back and forth, but also slowly pulls them downward in the centre. They then pass through the moving agitator fins at the base, which provide the scrubbing action, before rising up the outer wall of the tub again and completing another circuit. If the upper section of the agitator is spiral-shaped and turns in only one direction on a ratchet, this is designed to work as an auger, further assisting rollover. Imagine the water and fabrics moving in a donut shape between the tub and agitator, and that’s the principle a top loader works on.
I think it would be hard to propel a sphere vs a drum that can be connected to the base to propel movement.