# BubbleFun

People in charge: DarrylYong, NickHerman, TracyBackes, AaronTamuraSato

Idea: We will have a number of different stations that students will visit during the course of 55 minutes. Each station will highlight a different activity relating to bubbles, or a different scientific principle relating to bubbles.

## To do list

• Get a good recipe for bubbles (we may just be using commercial solution)
• Finalize the bubble stations and make a "script" for each station
• Test out the antibubble procedure (not too good?)
• Bend the clothes hangers (we might be switching to pipe cleaners)
• What else?

Materials needed

• wire clothes hangers (we have, but they don't work too well)
• bubble solution (we have commercial-brand and ingredients for home-made)
• squirt bottles (we have 2)
• lots of containers (we have a medium size container, and Aaron has a large storage container)
• distilled water
• baking soda and vinegar
• yarn/pipe cleaners/something to wrap around the wands (or make the wands out of)

## Station 1: Energy and shape

needed: a few pads of paper, big tub, we will fill with baking soda and vinegar to make CO2. Allow the bubbles to rest so that we can look at them carefully.

First, ask "Why is a bubble spherical?" (it's the most efficient way to enclose a volume).

Then, ask students to predict the shape created when two bubbles merge together. Ask students about the volume of air that is enclosed by the bubbles before and after they merge. Do the volumes increase, decrease, or stay the same? Have them draw their ideas for what the merged bubbles will look like on a pad of paper before we actually form merged bubbles. Three bubbles? Then have them validate those predictions.

Goal: Get them to understand that the bubbles are trying to enclosed a FIXED volume of air and try to minimize the total surface area. When two bubbles merge, they can save on surface area by sharing the common side.

The twin bubbles are the most efficient way to capture two volumes of stuff.

One comment on density - the bubbles float on the carbon dioxide due to the relative density of the air.

## Station 2: Minimal surfaces

needed: Wire hangers, big tub of soap, plastic & magnets if we want to do the Steiner point (120-degree point formed by three films)

Start with a wire with a square hoop. Dip in soap and ask why they think the soap film is "flat"? Students may need help with the idea of surface area.

Notice that when you blow lightly on the hoop, the surface bulges. Help the students realize that the surface area is increasing when this occurs. Then point out that the film always returns to its original flat position.

3D wire shapes have interesting surfaces when dipped in solution. I've made a cube, a tetrahedron, and a rectangular pyramid. Kinda. They're a little... messy (especially the cube). I hope they work.

The Steiner point: With the same computer program as in class, they can experiment with the shortest way to connect three points. Fiddling with the plates and magnets, you can demonstrate how soap films naturally solve the problem. Point out the equal angles.

Dip wires with other shapes in soap and let them experiment. They can also bend some hangers of their own and see what happens. Help them to come to the idea that the soap film has the least surface area.

## Station 3: Surface tension

Question: Why can't you make a bubble using just water?

Surface tension is the force that makes the surface of liquids seems as if they have a skin. A cup of water can often be filled above the brim without spilling because of this effect. The reason that it happens is because water molecules like to stay together and don't like to be apart, so they try to group themselves together. As long as there isn't too much water in the cup, the water molecules would rather form a "mound" above the cup than for the water above the brim to spill over.

Surface tension is also the reason why you can float a paper clip on the surface of a liquid.

Soap molecules reduce the effect of surface tension, and causes the water molecules to spread out more. That is why if you add a little bit of soap to this very full cup of water, it will spill out, and the paper clip will sink.

Surface tension is the reason why you can't make a bubble using just water. The water molecules want to clump together and they don't like to form a "shell".

A soap bubble actually consists of a thin layer of water trapped between two layers of soap molecules. This surfactant possesses hydrophilic heads and hydrophobic tails. The hydrophilic heads are attracted to the thin water layer and keep the bubble intact. When the hydrophobic tails are agitated, the bubble pops. It may also burst when it hits pointy surfaces. (from wikipedia, explain hydrophilic and hydrophobic)

## Station 4: Giant bubbles

Why? Just because it's fun.

maybe have a contest to see who can make the biggest bubble?

## Station xxx: Antibubbles (not working so we scrapped it)

Floating bubbles, antibubbles (with salt water so they sink), etc..

Goal: Get students to think about bouyancy?

Brainstorming:

• 4 stations about different things pertaining to bubbles