Blowing bubbles using a straw
Overview
This page will print, but looks a little funky. Click the button for a PDF version which looks a bit better. This is a stop-gap while we work on a better solution!
What you’ll need
- Two cups
- A tablespoon and a teaspoon
- Sugar (half a teaspoon)
- Washing up liquid (about 1 teaspoon)
- Warm water
- A straw (a tube from a pen, Calpol syringe or rolled up paper will work too!)
- Bin bag (this is to protect the table you are using)
- A table
Duration
30 minutes or so.
Suitable for…
Age 4 and up.
Safety notes
You know your children better than anyone, and you should judge whether they’re ready for this activity. You might want to think in particular about:
- Check the temperature of the water. It only needs to be warm enough to touch, no hotter.
- Make sure all objects to be used as straws are very clean before they are put into mouths.
- Don’t let children taste or drink the bubble mixture.
- If any washing-up liquid gets into a child’s eye, rinse with water. Get the child to lie on their back near a sink or bath and gently pour cool water from a jug, or similar, over the open eye continuously for 10 minutes.
- Children who are allergic or sensitive to soap or detergent products should not do these activities.
- Ensure children wash their hands after the activity.
What to do
Step 1 – Making the bubble solution
Put 40mls of warm water in a cup – that’s about 2 tablespoons plus 2 teaspoons.
Add 1 teaspoon of washing-up liquid, and stir gently.
Find a clean, flat surface to use – this could be a table, plastic mat or plate. If you’re using a table, lay out a plastic bin bag to protect it from the bubble mixture. If you’re outside, you might want to tape or weigh it down to make sure it doesn’t blow away.
Wet an area about 10 cm across by dipping your fingers into the bubble mixture and spreading it on to your surface. Then try blowing bubbles – see Step 2.
If your mixture doesn’t work, try adding half a teaspoon more washing up liquid to the mixture. You could also try dissolving ½ a teaspoon of sugar into your mixture.
The type of washing-up liquid also affects your bubbles: Fairy liquid is good, as are many supermarket own-brand products. But some brands just don’t work too well. If you’re out of luck with your washing-up liquid, try bubble bath if you have some.
Step 2 – Blowing bubbles
Dip one end of your straw or tube into the bubble solution so it’s completely coated.
Place the coated end of the straw or tube onto the bubble mixture on your surface. Blow gently into the other end of the straw to create a bubble.
Dip the straw back into the solution every time you want to blow another bubble.
Step 3 – Challenge step! Blow a double bubble
Dip the straw back into the bubble solution. You need to make sure that the bubble end is completely coated for this to work.
Aim for the centre of the first bubble and carefully push your straw inside. Gently blow a second bubble on the table surface, inside the first bubble.
Can you blow a third bubble inside the second bubble? How about a fourth bubble inside the third bubble?
How does it work?
Mixing washing-up liquid with water forms a solution. When you blow a bubble, air is trapped by a thin film of your bubble mixture. This film is made of a layer of water sandwiched between two layers of soap.
A bubble pops if the soapy outer skin is broken. This can happen as the water in the bubble evaporates, or if the bubble touches something dry or oily. It can also happen when the bubble becomes too big and there isn’t any more soap to create the sandwich layer. If your bubbles last a really long time, you might see the colours shift as the water drains around the sides of the bubble back onto the flat surface. Eventually, the bubble gets so thin you can barely see it – right before it pops by drying out!
Wetting the straw by dipping it in the bubble solution allows it to slide it into the bubble without popping. You can try doing the same with your fingers: can you poke your finger into your bubble without bursting it?
Things to talk about
- What happens when you blow more than one bubble onto your table?
- What happens if you blow more and more bubbles?
- Why do you think bubbles join together?
- Sometimes, a bubble that pops turns into a smaller bubble. What do you think might be happening?
Other things to try
Who can blow the biggest bubble?
Coat a small plastic ruler with bubble solution and slide it into the middle of your bubble to measure its height.
Do larger bubbles take longer to pop?
Use the timer on your phone, a clock with a second hand or count elephants (one elephant, two elephants, three elephants…) to measure the time it takes for each bubble to burst.
Which ingredients make the bubbles last longer?
Try using more soap, sugar or water in your mixture. Can you make a better bubble solution than us?
What you’ll need
- Two cups
- A tablespoon and a teaspoon
- Sugar (half a teaspoon)
- Washing up liquid (about 1 teaspoon)
- Warm water
- A straw (a tube from a pen, Calpol syringe or rolled up paper will work too!)
- Bin bag (this is to protect the table you are using)
- A table
Duration
30 minutes or so.
Suitable for…
Age 4 and up.
Safety notes
You know your children better than anyone, and you should judge whether they’re ready for this activity. You might want to think in particular about:
- Check the temperature of the water. It only needs to be warm enough to touch, no hotter.
- Make sure all objects to be used as straws are very clean before they are put into mouths.
- Don’t let children taste or drink the bubble mixture.
- If any washing-up liquid gets into a child’s eye, rinse with water. Get the child to lie on their back near a sink or bath and gently pour cool water from a jug, or similar, over the open eye continuously for 10 minutes.
- Children who are allergic or sensitive to soap or detergent products should not do these activities.
- Ensure children wash their hands after the activity.
Make your own bubble wands
If you want to use up your bubble mixture, you could blow some bubbles outside or even out of your window. There are lots of instructions around the web for making wands for giant bubbles using loops of string. We particularly liked this page from Rhubarb and Wren, who even have their own bubble mix page.
Blowing bubbles with no apparatus at all – make a loop with your fingers and blow through that!
Science For Families: Floating
© and courtesy Nevit Dilman
How cool is your little Cartesian Diver? It’s amazing that you can make it float or sink with just a little squeeze of the bottle.
Knowing how things float and sink can be really useful, and there are loads of different ways to explore the idea. For example, using gas:
Sparkling drinks are fizzy because of a gas (carbon dioxide) that’s dissolved in the water. The gas forms little bubbles which rise to the top, where they burst. If you put some raisins in a glass of sparkling water and watch what happens.
The tiny little dents and indentations in the side of the raisin give the gas something to form a bubble around. When the raisin has enough bubbles it can float up to the surface. The bubbles then pop, the raisin sinks and the whole merry dance begins again. Try making an artificial raisin out of blu-tac. Remember it’s all the little tiny nooks and crannies that allow the bubbles to form. It’s surprisingly difficult to get it to dance like the raisin, but it is possible, so keep trying!
A similar thing happens when you put Mentos sweets in a bottle of Coke. The tiny imperfections on the surface of the Mento acts as sites for bubbles to form. Lots of bubbles. Lots of bubbles. What, you’ve never put Mentos in Coke? Go outside and do it right now!
Displacement
The key to being able to make things float is displacement. When a boat floats it shoves water out of the way – it displaces it. The displaced water weighs as much as the boat. But if the boat’s too heavy for its size it can’t displace enough water to balance out, and it sinks. This means you can build boats out of metal, as long as they’re large enough to displace enough water to offset their weight.
You can have a go at boat design using kitchen foil and pennies. Make a boat shape from the foil, and check it floats. Then load it up with pennies. How many could you get in your boat before it sank?
Try a redesign, and try again. Remember, you want your boat to take up as much space as possible, so that it displaces a lot of water.
Density
© Marie-Lan Nguyen / Wikimedia Commons / CC-BY 2.5
Another way to make your boat float is to make the water heavier.
Wait – what?
When you add salt to water and dissolve it, you are increasing the density of the water – it takes up the same space, but weighs more than it did. This is why it’s easier to float when you’re swimming in the sea than when you’re in a pool, the sea is saltwater. If you’re in the dead sea, which has an unusually high salt content, then you float very easily indeed.
You can test this out using a bowl of water and an egg. If you put an egg into a glass of tap water, it will sink. However, if you add a lot of salt and dissolve it in the water first, you can get the egg to float – a great trick to bamboozle your friends!
Bubbles
Bubbles
Whether you’re in the bath or washing-up in the kitchen, nothing makes a daily chore more fun than bubbles. No, really. Bubbles are fun. Serious fun. The science behind bubbles is fascinating, because it relies on the physics of water. We’re so used to water being all around – heck, it falls out of the sky! – that we don’t stop to think about how weird it is. That ice cubes float is amazing, because with almost every other material the solid is more dense than the liquid, so they sink. Whereas ice takes up just a little more space than liquid water, so it floats.
You can get an idea for just how weirdly water behaves even more easily: fill a glass all the way to the brim, then keep going. You’ll see the water bulge upwards, like this. That happens because water molecules interact with each other and with the glass, just a little bit. It’s a very small effect, but it’s enough to cause water to tend to clump together, to flow a little distance up the side of a glass, and to bulge like this.
Gently place an object on the surface – like this rather tatty-looking paperclip we found kicking around in the Think Physics office – and you can see the curve of the water surface around the object. That curve is what provides the force balancing the weight of the object.
Water surfaces do amazing things when you start to muck around with the water itself. Add a little detergent – washing-up liquid is enough – and that spreads out on the surface forming a layer between the water and the air. We all know what happens next:
We bought a commercial bubble wand to blow giant bubbles, but you can make something very similar yourself using fabric tape and an old broom handle. Here’s Joe practicing his giant bubble technique in Think Lab.
Yes, we mopped up afterwards.
Exploring bubbles with the RI
The simplest bubble recipe is easy to make: washing-up liquid and water! Start with a bowl of lukewarm water and gentle add washing-up liquid. As you add, keep checking your mixture with a bubble wand until you find a solution that works for you. You won’t need very much detergent, so don’t go mad with it!
Then, find anything with a hole in it and start blowing. The gallery above has some examples, and the Royal Institution’s video here has some great ideas for experiments.
Other fun with bubbles
Bubble snakes: find a plastic tube that’s open at both ends and fix a flannel or dishcloth over one end with an elastic band. Dip the flannel into your bubble solution and then blow down the tube. Watch as the bubbles join to create a bubble snake. Try adding some different paint colours to the flannel to create a colourful snake!
Giant bubbles: these are a little more technical. You can still get away with washing-up liquid and water, but you search around the web you’ll find dozens of recipes for extra-impressive bubble mixtures. Most of them add a small amount of glycerine, which can help your bubbles last longer. Other ingredients might be tricky to get hold of in small quantities, so if you’re super-serious it’s worth looking at commercial mixtures. At Think Physics, we’re quite impressed with Dr Zigs’ solution. Our bubble wand came from Amazon, but using garden canes and some fabric tape you can easily make your own.
Bubble painting. This looks terrific, though no less messy than the other ideas. Add a bit of food colouring into your bubble mixture, blow some foam, then carefully splat the foam with a sheet of paper. Nice results.
Viewing soap film colours
Prototype soap bubble viewer, with Joe for scale
The colours you see in a soap bubble are a result of the way light interacts with the thin film of the bubble surface. Soap films are about the same thickness as the wavelength of visible light, and the reflections from the front and back surface of the film interfere, leading to the spectrum you see.
We did a quick write-up of a highly effective way of viewing the colours back in November. The longer version goes like this:
- Stretch some black bin bag across a table.
- Splat some bubble mixture on the plastic, smear it around a bit, then blow a half-bubble about six centimetres across.
- Shield the half-bubble with something that will diffuse light – Ikea Melodi lampshades are perfect.
- Light strongly from the side – so place your table near an open window, or use lamps alongside the lampshade.
- Look (or photograph) straight down at the bubble.
You’ll see particularly strong colours, and with a bit of tinkering the bubble can last for many minutes. As the mixture drains downwards you’ll see the colours slide down the sides of the bubble.
