Balloons in the Bath (Learning about Liquids and Gases)

by Deb on September 2, 2009

It’s starting to look like I’m a bit obsessed with balloons, isn’t it!  But they are just so cool, there are so many good things you can do with them.  This one is actually my husband’s idea.

We play with water bomb balloons a lot, the baby loves them.  For some reason she carries them around and sucks/chews on them, maybe they feel cool? But of course they break easily, so my husband filled up some normal balloons about halfway to use in the bath.  This is not only brilliant fun, it is a great way to learn about liquids.

Think about it – it’s really hard to see what’s going on in a liquid, so even though they are very different to solids and move, little kids often don’t realise that.  Balloons are great, their weight is negligible but they are a good size and easy to hold so you can really test things out.

Shape: Liquids change shape and take on the shape of their container.  Balloons can be squashed and kneaded, in this photo the balloon has been stretched and squashed to fit into a long thin container.

balloon in container

Movement: Liquids have internal currents and move in different directions.  Balloons are good to demonstrate this one because if they are full of water they will almost have neutral bouyancy, so they don’t sink or float.  You can see how they move all over in the bath, and kids can scoop the water to move them in different directions.  Try racing two balloons from one end of the bath to the other without touching them!

This photo shows a balloon that is floating halfway up the bath.  You can see it is underwater because the bubbles have shadows on the balloon, shown in the circle.

underwater balloon

Gases: This is one of the few times you can actually see a gas.  A great trick with a water balloon is to leave a bubble in it.  When you gently roll and move it, the bubble always stays on the top, showing that the air is lighter than the water.  Challenge your kids to get it down to the bottom!

Then you can look at how balloons float.  Because the balloon itself is so light, they pretty much float so the water level inside the balloon is the same as outside, and you can see through them to check.  Fill up balloons with different amounts of water and air and you can compare them by floating them next to each other.  Or challenge your kids to get them underwater.  Older kids could get very inventive here by attaching things to the balloon to hold it down.

floating balloon

Can you work out what’s happening here?

balloon suction

This is actually caused by air pressure.  What’s happened is that the balloon has been stuffed into the red pot, pushing the air out.  Then when it’s pulled up it doesn’t take up as much space, but the water has made a seal around the top so no more air can get in.  This means the air still left in the pot is more spread out and thinner than the air outside, so the air outside is pushing on the pot and keeps it up.  The water seal does break fairly quickly and air gets in, so it crashes down with a satisfying splash 🙂

Did you know straws work via air pressure as well?  You suck the air out and it makes the inside of the straw low pressure, the outside air pushes the drink down and it goes up into the straw.

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{ 8 comments… read them below or add one }

momi September 6, 2009 at 12:10 pm

Ooh, can’t wait to try this!

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Catherine September 8, 2009 at 5:53 am

We love balloons at my place but have never thought to put them in the bath – we’ve got to try it.

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Kate Schultz via Facebook April 16, 2011 at 9:25 am

What a coincidence, I was just talking to my sister-in-law about all this as she’s recently started scuba diving!

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Science@home via Facebook April 16, 2011 at 8:52 pm

I’d love to do scuba diving, my brother used to. Snorkelling is fascinating, scuba must be better.

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Kate Schultz via Facebook April 16, 2011 at 11:12 pm

The footage I’ve seen of her dives is amazing. The whole process of scuba diving is much more technical than I ever realised.

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Ang Hall via Facebook April 18, 2011 at 7:21 am

We did this activity after reading your post, thanks for the great ideas!

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Science@home via Facebook April 18, 2011 at 7:36 am

You’re welcome. Sometimes you just need a simple idea to see all sorts of new things to do.

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Ang Hall via Facebook April 18, 2011 at 7:38 am

Exactly! Fresh thinking. My daughter loved it, water and balloons what’s not to love? lol.

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