The secret is surface tension ( کشش سطحی ). Surface tension is like the "skin" ( پوست ) of water holding it together. Water molecules* come very close together ( به هم فشار دهید ) and make the water dense ( متراکم ). The molecules come together because they are polar.
📍
The negative side of one molecule is attracted to ( جذب شدن به ) the positive side of another molecule. So they move close together. That makes water dense. ( متراکم ) And that lets water resist ( مقاومت کردن ) anything that touches ( لمس کردن ) it.
Adding soap to water changes the surface tension of the water.
When soap mixes with water, the soap pulls apart the water molecules. One end of a soap molecule attracts ( برای جذب ) a water molecule and the other end of the soap molecule pushes the water molecule away from it. That breaks ( شکستن ) the surface tension of the water molecule. The result is soap sandwich. The center of the sandwich is air. Then there is a thin layer of soap, a layer of water and another thin layer of soap. But instead of being square, like a sandwich, the shape is round: a bubble!
So when you look at a bubble, what you're seeing is a tiny bit of air trapped inside a soap sandwich.
Soap molecules look for the easiest way to surround ( احاطه کردن ) the air. The easiest way is to make a sphere ( یک کره ). It takes less energy to make a sphere than a box. So you will NEVER see a square bubble!
😮 Did you know you can make frozen ( منجمد ) bubbles?
IMPORTANT WORDS —
molecule ( مولکول ها ): atoms that hang on to each other and have the same qualities ( کیفیت ها ). A molecule is the smallest part of anything that can have a reaction ( عکس العمل ).
polar: when one side of a molecule has a positive ( مثبت ) charge ( چارج) and the other side has a negative ( منفی ) charge ( چارج ).
surface tension: کشش سطحی
dense: متراکم
