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Author Topic: Why do my legs float in the bath?  (Read 6763 times)

Faith Williams

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Why do my legs float in the bath?
« on: 27/11/2011 19:30:02 »
Faith Williams asked the Naked Scientists:
   
When lying in bath of water why do my legs float?

What do you think?
« Last Edit: 27/11/2011 19:30:02 by _system »


 

Offline damocles

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Why do my legs float in the bath?
« Reply #1 on: 27/11/2011 20:55:47 »
Legs are made up of: fat, water, muscle and bone in a variety of forms and for a variety of functions. The fatty parts are less dense than bathwater and will tend to float. The watery parts are the same density -- neutral buoyancy. Muscle is slightly more dense than bathwater, and bone is much more dense. These parts will tend to sink.

Whether a leg will float or sink depends on the relative amounts of these materials.

However, there might be another factor. It is possible that lying on your back with very relaxed muscles might lead to a slight tendency to flex slightly at hips and knees so that you are actually lifting your legs a little with no apparent effort, and they provide an illusion of floating.
 

Offline RD

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Why do my legs float in the bath?
« Reply #2 on: 27/11/2011 21:06:03 »
Density of water 1g per ml, density of muscle  1.06 g per ml, density of fat 0.9g per ml

Muscle is more dense than water and will sink in water, fat is less dense than water ...

https://en.wikipedia.org/wiki/Hydrostatic_weighing

https://en.wikipedia.org/wiki/Body_fat_percentage#Typical_body_fat_amounts
 

Offline Soul Surfer

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Why do my legs float in the bath?
« Reply #3 on: 27/11/2011 23:25:31 »
There is also another physiological factor to consider.  When you are lying on your back you are used to the weight if your legs and your body tends to compensate for this when you lie in the bath the water reduces this and you tend to feel much more strongly that your legs are lighter.  There is always this traditional childhood experiment hat shows this compensation effect. stand by a wall and lean against it for a few minutes with the back of your hand supporting your weight and your arm muscles tensed.  then stand up and relax your arms yo will find that the  arm you have been leaning on will start to rise on its own.  A very unnerving effect.
 

Offline damocles

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Why do my legs float in the bath?
« Reply #4 on: 28/11/2011 00:04:03 »
The reason to believe that the physiological effects are important is that in terms of bone+muscle to fat ratio, one might expect the legs to be among the more dense body parts. This is borne out by an easily tested observation -- if you float in the ocean or a swimming pool by lying immobile on your back, your feet and legs (and possibly your arms) tend to sink while the rest of your body will float -- helped by a lungful of air, of course.
 

Offline Geezer

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Why do my legs float in the bath?
« Reply #5 on: 28/11/2011 01:36:43 »
Hollow legs? We had friends over for Thanksgiving and, judging by the amount of turkey they managed to consume, I'm pretty sure they must have hollow legs.
 

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Why do my legs float in the bath?
« Reply #5 on: 28/11/2011 01:36:43 »

 

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