39. Why does the oil paint do not flow off the vertical

39. Why does the oil paint do not flow off the vertical surfaces, but the oil itself flows down?
If you do not open the file - install the RAR archiver. Inside the archive you will find a solution in Word format.
Questions and problems from the manual:
"Laboratory Workshop on Colloid Chemistry" Nekrasov AP, Veretenchenko BA, Kharkov NTU "KhPI", 2004
"Characteristic properties of disperse systems" Nekrasov AP, Kharkov, 1996
Tasks are executed in Microsoft Word, graphics - in Microsoft Exel or OriginPro; formulas are typed in the MathType editor (if the formulas contain unreadable characters, then you need to install this editor); files are archived by WinRAR.