# Jim' slippery feet

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When relaxing in the bath with my knees raised and my feet maybe 2/3 down the bath, my feet slide to the far end.

Why do they slide very slowly and at essentially a constant speed?

• My feet move very slowly - approx 1mm/5sec or 1mm/10 sec --- initially hard to discern movement at all.
• It can't be elasto-hydrodynamic - which would cause rapid movement.
• It can't be just gravity induced forces and friction --- the forces would have to be exactly equal !

• Can it be viscosity in the thin water film under my feet ?
• Can it be stick/slip at the many micro contacts of my feet to the bath ?

If you are a "shower person", then this will mean nothing to you. Pass it on to a "bath person" for confirmation.

I think this is a "Do try this at home".

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19 minutes ago, JimA said:

When relaxing in the bath with my knees raised and my feet maybe 2/3 down the bath, my feet slide to the far end.

Why do they slide very slowly and at essentially a constant speed?

•

My feet move very slowly - approx 1mm/5sec or 1mm/10 sec --- initially hard to discern movement at all.
•

It can't be elasto-hydrodynamic - which would cause rapid movement.
• It can't be just gravity induced forces and friction --- the forces would have to be exactly equal !

• Can it be viscosity in the thin water film under my feet ?
•

Can it be stick/slip at the many micro contacts of my feet to the bath ?

If you are a "shower person", then this will mean nothing to you. Pass it on to a "bath person" for confirmation.

I think this is a "Do try this at home".

Do you mean this? 1mm every 5secs would be 1.2cm/minute, so it would take 25mins for your feet to advance 1ft along the bath, by which time I’d have thought the water would be getting cold.

But I suspect the phenomenon may involve some unnoticed feedback between the apparent weight of your legs and your muscles, i.e. not a pure physics problem. You may subconsciously relax progressively as your feet move and more of the weight is supported by the water. But it’s a speculation. It could also be some kind of slick-slip due to the movement of the skin, I suppose.

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3 hours ago, JimA said:
• My feet move very slowly - approx 1mm/5sec or 1mm/10 sec --- initially hard to discern movement at all.
•

It can't be elasto-hydrodynamic - which would cause rapid movement.
• It can't be just gravity induced forces and friction --- the forces would have to be exactly equal !

• Can it be viscosity in the thin water film under my feet ?
•

Can it be stick/slip at the many micro contacts of my feet to the bath ?

You don't say whether or not your rear end is moving likewise.

Either way, my money would go on dot items 3 & 5 working in tandem. Gravity provides the driving force for pulse-induced creep. Every heartbeat lifts and lowers you ever so slightly allowing gravity to slowly inch (millimetre?) you down the gravity well.

It's an unsupported hypothesis, but I'd be willing to accept a reasonable research grant if you'd like more flesh on the bones.

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4 hours ago, JimA said:

Why do they slide very slowly and at essentially a constant speed?

For the same reason that early mediavel cathedrals fell down, until they discovered side thrust and put ties or buttresses into the architecture.

The bottom member of a standard roof truss for a double pitched roof is just the same.

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Anyone else confirm my observation ?

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