What's Going On?
Because of the shape of water molecules, water has a very high surface tension...it tends to stick to itself very tightly, like a stretched-rubber band. If you blow a bubble into plain water, it will pop quickly, like stretching the rubber-band so far it breaks. Most juices are mostly water, so bubbles blown into them also have high surface tension and pop quickly. Milk has a lot of proteins in it that connect together, creating a type of film that can stretch. Milk has less surface tension than water because of these proteins. It is like the rubber-band is not stretched as far. The milk has enough protein in it that you can even make juice/milk bubbles easily!
Extension Activities & Experiments!
You can continue to explore these concepts with lots of other experiments, including these:
1. Eggs have loads of protein! What happens if you try to blow bubbles in water? What if you add a little egg white?
2. Can you find a juice or other kitchen liquid that makes bigger bubbles than milk?
3. Is there a difference in warm milk and cold milk? What about skim or whole milk?
4. Dish soap is a surfactant that also lowers the surface tension of water. Try Bubble Science with Pumpkins, Bubble Spider Webs, and Bubble Painting for experiment ideas with dish soap!