Last night I was in my bathroom conducting an experiment about the speed of water on butter.

The experiment went something like this:

  1. Cover half a sheet pan with butter and leave the other half untouched.
  2. Incline the sheet pan at an angle of roughly 50°.
  3. Start the stopwatch, and with an oral syringe, put a drop of water on the highest part of the sheet pan on the buttery side.
  4. Stop the stopwatch when the drop of water reaches the bottom of the sheet pan.
  5. Repeat steps 3 and 4 on the clean side of the sheet pan.

For some reason the water ran alot slower on the buttery side. The water droplets for both sides started with close to no speed.


1st try: more than 15 minutes. The water started out very slow and lost speed quickly. The water was about 1/2 the way to the bottom after 15 minutes.
2nd try: more than 15 minutes. The water appeared to stop completely at one point. It was about 1/2 the way to the bottom after 15 minutes
3rd try: more than 15 minutes. The water appeared to stop completely at one point, around 1/4 of the way there. The water was around 3/4 the way to the bottom after 15 minutes.

1st try: 28.32 seconds. The water flowed slowly at the beginning but quickly accelerated and flowed quickly.
2nd try: 35.76 seconds. The water did not accelerate as much as in the first try. It appeared to stop completely at one point and then accelerated again.
3rd try: 32.26 seconds. There is water all over the bathroom floor.

Assuming these times are accurate, why did the water on the buttery side flow SO slowly? I had initially expected it to flow faster because of the oil in butter and also because butter is hydrophobic.



My handwaving explanation to your handwaving experiment : Because butter is hydrophobic water tends to be repelled and gathers into spherical drops, which will have to roll down. Water on the non hydrophobic surface runs into rivulets,( rain on car's windows) a path with no friction for the mass of water coming behind. On a hydrophobic surface it cannot take advantage of this.


Water drops on the hydrophobic surface of grass

The forces acting on the drops on a hydrophobic surface are: its weight, air pressure versus the vacuum beneath the drop, which makes it stick unless the angle is large enough for the weight to dominate downwards, when it will roll. On a non hydrophobic surface the water rolls on the first layer of water wetting the surface, and makes rivulets. No suction from the vacuum between surface and water, on the volume ( which keeps the shape of rivulets instead of drops).


adhesive forces of water particle are different with base of sheet and butter molecule From your experiment results we can conclude water-butter molecule adhesive force is higher pl. support your experiment with video if possible (- providing YouTube link ?) if you pore honey instate of water it will end up in different result Also the surrounding temperature have influence on the experiment !

  • 2
    $\begingroup$ Hi Gaurav, thanks for your answer. Why is the water-butter molecule adhesive force higher? Isn't butter hydrophobic? $\endgroup$ – mochacat Jan 18 '17 at 5:17

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