BUBBLES
What’s the science behind (or inside) a bubble? Bubbles provide the opportunity to study science concepts such as elasticity, surface tension, chemistry, light, and even geometry.
What is a bubble?
A bubble is air wrapped in “film”. Can you blow bubbles just with water? Yes you can but water bubbles will only live for very short time due to strong water surface tension.
Real bubble is air wrapped in soap film. Soap film is made from soap and water (or other liquid). The outside and inside surfaces of a bubble consist of soap molecules. A thin layer of water lies between the two layers of soap molecules, sort of like a water sandwich with soap molecules for bread. They work together to hold air inside. Washing up liquid lowers the surface tension of water. It makes the water stretchy and wibbly-wobbly so that you can blow bubbles.
Why is a bubble round?
Bubbles can stretch and become all kinds of crazy looking shapes. But if you seal a bubble by flipping it off your wand, the tension in the bubble skin shrinks to the smallest possible shape for the volume of air it contains. That’s why even if it had a goofy shape before you sealed it, once sealed shut, the bubble will shrink into a sphere shape. Compared to any other shape, a sphere has the smallest surface area for the amount of volume.
Other than being poked or landing on something sharp, bubbles pop when the water between the soap film surfaces evaporates. To note, when it’s cold, those molecules take longer to leave. If you blow a bubble on a calm winter day, a bubble can even freeze and last for several minutes before it wisps away. Also, the colder the outside temperature is, the higher a bubble might fly. That’s because the warm air from your breath is lighter than cold air.
A bubble gets its colour from light waves reflecting between the soap film’s outer and inner surfaces. The distance between the layers gets smaller as the water evaporates, making the colours change. Bubbles can also reflect what’s around them, like the faces peering at them.
Why do bubbles stick together? Since a bubble tends to minimize its surface area, bubbles will join together to share one common wall. Three bubbles will meet at the centre, always at an angle of 120 degrees. When bubbles are about the same size, they form perfect hexagons. Bees do the same thing when they build a beehive. Bees, like bubbles, are also very efficient with their spaces. They use the minimum amount of wax to create their spaces.
Exercise 1
Equipment: Each class will need:
1 squeezy bottle of fairy liquid
1 squeezy bottle of glycerine
Small Measuring cups
Large bowls (one per pair)
Plates
Spoons
Make a bubble solution
Give out one plastic bowl to every pair of children. Make sure each child is wearing a blue apron provided
Use the small plastic cups to add 2 cups of water to their large plastic bowl.
Next add ½ cup of washing up liquid and 3 ½ tsp of glycerine----Glycerine stops bubbles from drying out so they don’t pop as quickly.
Now each child will spoon some mixture onto their plate with their spoon. Have a go at blowing with different types of straws – do some work better than others? See if you can try and blow a bubble inside a bubble!
Exercise 2
Cut off plastic bottles
Muslin squares
Rubber bands
Get your plastic bottle with the base cut off. On the base end, cover with the piece of muslin provided and secure with an elastic band. Pour some bubble mixture on your plate and with the muslin end of the bottle touching the surface of the plate, blow down into the smaller neck of the bottle and move your head up so you create a bubble tower. MAKE SURE YOU DO NOT SUCK IN. IF YOU NEED A BREATH, TAKE YOUR MOUTH AWAY FROM THE BOTTLE!