Surface Tension and Soap
Find out how bubbles work with this experiment. You won't actually blow any bubbles, but you will learn the science that makes a bubble!
What You Need:
- 2 short glasses of water
- A pie plate or tray
- Liquid dish soap
What You Do:
- Put the first glass of water in the center of the pie plate.
- Slowly pour some water from the second glass into the first glass until it is very full and the water forms a dome above the rim of the first glass. Set the glass with less water aside.
- Carefully stick your finger straight down through the dome of the water in the full glass and watch what happens.
- Now put a small drop of dish soap on the tip of your finger and do the exact same thing - stick the finger with soap on it straight down through the dome of water. This time what happens?
Water is made up of lots of tiny molecules. The molecules are attracted to each other and stick together. The molecules on the very top of the water stick together very closely to make a force called surface tension. Surface tension is what caused the water to rise up above the rim of the glass in the experiment - the water molecules stuck together to make a dome instead of spilling over the side. Why didn't the dome break when you stuck your finger through it? Why didn't the water spill over the glass? Well, the surface tension was strong enough that it just went around your finger. The water molecules still stuck to each other and nothing spilled! What happened when you put your soapy finger into the water? The soap on your finger broke the water's surface tension and some of the water molecules didn't stick to each other any more and they were pushed out of the glass!
The force of surface tension also creates bubbles. In plain water, the surface tension is strong and the water might make some bubbles, but they will not last very long and they will be very small, because the other molecules in the water will pull on the bubbles and flatten them. Soap needs to be mixed with the water to make bubbles that can float through the air. When you add soap, the water becomes flexible, sort of like elastic, and it can hold the shape of a bubble when air is blown into it.
Super Bubble Solution
Make your own bubble-blowing solution out of soap and water, then see what happens when you add a special ingredient to the bubble solution!
What You Need:
- Liquid dish soap (Joy or Dawn brands work best. Try to find one that doesn't say 'Ultra')
- Distilled water (tap water is okay, but distilled water makes the best bubbles)
- 2 clean containers with lids
- Glycerin or light corn syrup
- Measuring cup
- Mixing spoon
- A plastic pipet (cut off the closed end to make a bubble blower) or a drinking straw
- Tape and a marker
What You Do:
- Measure 6 cups of water into one container, then pour 1 cup of dish soap into the water and slowly stir it until the soap is mixed in. Try not to let foam or bubbles form while you stir.
- Once the soap and water are mixed, go outside to test it. Dip the cut end of your bubble blower into the solution and let the extra drip off. Blow through the narrow end to make bubbles. Do you get a lot of bubbles? How big are they? How long do they last before they pop?
- Have an adult help you pour half of the bubble solution into the other container. Put a piece of tape on the outside of the new container. Use the marker to label it 'Super Bubbles.'
- Measure 1 tablespoon of glycerin or 1/4 cup of corn syrup and add it to the 'Super Bubbles' container. Stir the solution until it is mixed together.
- Dip your blower or straw into the new bubble solution and blow. Are these bubbles different from the plain soap and water bubbles? Are they bigger or smaller? Do they last longer or pop faster? Can you blow a really big bubble?
- To make even better bubbles, put the lid on the container and let your super bubble solution sit overnight. You can add glycerin or corn syrup to the other container to make those bubbles better, too. (Note: If you used 'Ultra' dish soap, double the amount of glycerin or corn syrup.).
The first bubble solution was just soap and water. As you learned from the Surface Tension experiment, soap helps bubbles form. You probably got some small bubbles that didn't last very long from the soap and water. Then you added glycerin or corn syrup to the soap and water and probably noticed that the bubbles you blew were stronger and better than before. Did they last longer? Were they bigger? The glycerin or corn syrup mixes with the soap to make it thicker. When the water that is trapped between the layers of soap in a bubble evaporates(or dries up), the bubble will pop! The thicker skin of the glycerin bubble keeps the water from evaporating as quickly. You can probably also blow a much bigger bubble with the second bubble solution that you made than with the plain soap and water one. Adding glycerin or corn syrup makes bubbles stronger and helps them last longer. It makes super bubbles!
After you make the super bubble solution and let it set for at least one day, try doing some of these cool bubble tricks! Can you think of any of your own tricks to do with bubbles?
What You Need:
- Super bubble solution in a container with a lid (from the experiment above)
- Pipe cleaners or wire
- Drinking straws
- Bubble blower (from the experiment above)
- Pointy objects like scissors and a pencil
Trick 1 - A Square Bubble?
You will need two pipe cleaners and your super bubble solution for this trick.
- Bend a pipe cleaner into a square. Wrap the ends around the sides of the square to hold it together. Fold the other pipe cleaner in half and loop it around one side of the square. Twist the ends together to make a handle. Use it as a bubble blower.
- Dip the bubble blower into the bubble solution and slowly blow a bubble through it until the bubble comes loose from the wand. What shape is the bubble?
The bubble was round even though it came from a square! Bubbles are always round when they detach and float through the air because the skin of soap always tries to take up the least amount of space it can and still keep the same amount of air inside the bubble. The soap molecules always stretch into a round shape automatically! A round shape takes up less space than a square shape. Try the trick again, but make a wand in any shape you want - what about a star or a triangle? Do bubbles from those shapes become round too?
Trick 2 - Don't Pop the Bubble!
You will need the super bubble solution, the lid from the container, a straw, and some objects with pointed ends.
- Set the lid on the table so that the part with the lip is facing up. Fill the lid with bubble solution.
- Dip your straw into the bubble solution container so that it is wet half way up the straw. Touch the straw to the lid and blow a bubble on the lid. Slowly pull the straw all the way out of the bubble.
- Now dip the pointed end of your scissors (or any pointy object) into the container of bubble solution. Make sure they are completely wet. Poke the scissors through the wall of your bubble. Watch what happens. Try it again with other pointed objects, just make sure anything you touch to the bubble is wet. Can you stick your finger through the bubble?
You should have been able to push the scissors through the wall of the bubble without popping it! When something wet touches a bubble, it doesn't poke a hole in the wall of the bubble, it just slides through and the bubble forms right around it. The bubble solution on the scissors filled in the hole that would have been made. If you try poking dry scissors through your bubble, you will see it pop instantly! (If it popped when you put the wet scissors in, something was probably too dry. Try it again and make sure anything that touches the bubble is completely wet with bubble solution.) For another trick, get one hand completely wet in the bubble solution then use the other hand to hold your bubble blower and blow a big bubble in the palm of your wet hand.
Molecule - a very tiny part of a substance that is too small to see with your eyes. A water molecule is smaller than one drop of water!
Surface tension - molecules in a liquid are attracted to each other and make the top of the liquid very tight. The surface tension is what causes water to form drops. It also makes a dome shape across the top of a container that is filled to the top.
Evaporate - when a liquid dries up and goes into the air. The liquid is then in the air, but it is a vapor or a gas now and you can't see it. When we say the air is humid, it means that a lot of water has evaporated into the air and now water vapor (gas) is floating around in the air. It makes the air moist and heavy, and it might make you feel sticky when you go outside.