Today’s Wonder of the Day was inspired by Holly. Holly Wonders, “why does soap make bubbles” Thanks for WONDERing with us, Holly!
Ahhh…is there anything better than a nice soak in a hot bath after a long day of school? After practice, homework, dinner, and some playing, there's nothing quite like ending the night with a frothy bubble bath before bedtime.
After you adjust the tap to make sure the water is the perfect temperature, you probably reach for a bottle of bubble bath. Although there are many different types of bubble bath available, they all contain one key ingredient: soap.
As you slip into the water, the cares of the day seem to wash away along with the dirt on your body. The soap in the bubble bath not only cleans your body, but it also creates a foamy layer of bubbles that are fun to play with.
What is it about soap that generates bubbles so easily? If you filled the tub with plain water, you would see barely any bubbles, if any at all. Why does adding soap to the water turn a plain tub of water into a bubbly spa?
To reveal the bubble-producing secret of soap, we'll need to explore the chemistry of soap molecules. When soap molecules mix with water molecules, they tend to separate out small bits of water to form bubbles.
Soap molecules have two very different ends: one end attracts water (hydrophilic) and the other end repels water (hydrophobic). When soap mixes with water, the opposite ends of the soap molecules sandwich a thin layer of water between themselves.
This creates a thin film that encompasses a tiny bit of air. What do we call that? A bubble! So when you look at a bubble, what you're actually seeing is a tiny bit of air trapped inside a thin film that's composed of two layers of soap molecules encasing a thin layer of water.
If you've ever used a bubble wand to create bubbles on a warm, sunny day, you've probably noticed that you can swing the wand to create an elongated bubble. The bubble doesn't stay in an elongated shape, though. It quickly forms a sphere, no matter what shape wand you use.
Why do all bubbles form spheres? That's where physics and geometry come into play. The surface tension present in the soap film surface of the bubble will force it to take the smallest possible shape for the volume of air it has inside.
That shape is always a sphere. Due to the laws of physics and geometry, the sphere uses the least amount of energy to enclose a particular volume of air, so that's why you'll never find square or triangular bubbles!