Why does a lemon which initially sinks , begin to float ?

Lemon - Sinks first and then Floats. Why ??

Question :

1) Why does a lemon sink in water , initially when dropped and float after sometime ?

2) The weight of the lemon (sink)         = 35 grams

    The weight of the lemon ( floating )  =  45 grams
3) If the weight increases, the lemon should be still sinking. But why is it floating

Conditions for floatation :

  1.  A body floats in water if its density is less than that of the liquid on which it floats
  2. The weight of the object should be less than the weight of the liquid displaced

Solution :         

   The lemon is highly concentrated (hypertonic ) when compared to that of water (hypotonic). It has a density higher than that of water  . Also the weight of the lemon is more than the weight of the water displaced by it. So the lemon sinks as soon it is dropped in water . Due to OSMOSIS , water enters the lemon and brings down its concentration. As a result its density becomes less than that of water. The weight of the lemon becomes less than the weight of the water displaced. Therefore the lemon floats in water.

If you understand the below picture, you yourself will solve this problem :

 

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Video for better Understanding  :

( Note : If you have a fast internet connection, please view the videos in HD  1080 p for the best clarity . To view it in HD click ' Change quality' and then ' 1080 p ')

My Experiment with Short Explanation of result :

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My Experiment with mathematical proof of result :

( Note : Change the quality for this video also )





With better clarity, I will upload another video .

Other things  noted :

1.      Some lemons readily absorb water and float. While others take hours to number of days.

2.      The presence of some gas ( may be CO2 , not sure) is observed .

Conditions for a body to float :

1.   A less dense body floats over a denser body. (i.e) The density of the floating body is less than the density of water.

2.   The weight of the body must be less than the weight of the water it displaces

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Verification of result through mathematical calculations :

 Step 1 :  Find the weight of water :

Let the weight of the lemon (sink )be                  W₁ grams

       The Volume of water displaced be                V₁ cm³

       The weight of the lemon (float) be               W₂ grams

       The Volume of water displace be                   V₂ cm³

          Radius of the container ( cylindrical jar )       3.8 cm

Volume of water displace by lemon ( sink) =     π x 3.8 x 3.8 x 0.7

                                                                 =     31.7552 cm³

Weight of the lemon ( sink )      =    35 grams

Density of lemon ( sink )    =     35 / 31.7552 g cm^-3

                                               =     1.102 g cm^-3

Volume of water displaced    =  31.7552  cm³

 Weight of water    =  Density of water  x  Volume of water displaced

                                  =  0.995   x  π x 3.8 x 3.8 x 0.7

                                  =  31.5964 grams

Weight of the lemon ( sink ) =  35 grams

Therefore ,   Density of lemon   >   Density of water

                       Weight of lemon    >   Weight of water displaced 

So it sinks in water.

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Volume of water displace by lemon ( float )   =   π  x 3.8  x  3.8  x  0.6

                                                                    =   27.2187  cm³

Density of water         =       0.995 g / cm³

Weight of water displaced   =  Density    x     Volume of water displaced

                                                  =   0.995    x    27.2187

                                                  =   27.0826 grams

Clearly  it is seen that two-fifth of the lemon is above the water.

This means that 

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So , The Density of lemon ( float )   <    Density of water

       The weight of lemon ( float )   <  The weight of water displaced

Therefore the lemon floats in water.

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Now find the weight of full lemon ( the lemon floating in water ) :

Density of lemon =  3 x Density of water

                                     5

Similarly,

 3 ( Weight of lemon ) =  Weight of water displaced

              5

Therefore , the weight of lemon ( the full floating lemon ) =    5 x (Weight of water displaced )

                                                                                                         3

                                                                                     =         5  x  27.0826

                                                                                                         3

                                                                                     =      45.13 grams

 EVEN WHEN THE WEIGHT OF THE LEMON IS INCREASED , IT FLOATS IN WATER BECAUSE IT DENSITY IS LESS THAN THAT OF WATER OR ITS DENSITY IS THREE-FIFTH THE DENSITY OF WATER .

( The Density of this particular lemon, that I have taken is three-fifth the density for water. For every lemon the ratio varies but its density is always less than the density of water )