Sink or float

Something I sometimes do with both my kids at bath time is ‘sink or float’. Now this makes it sound like we have idyllic bath times in our households, so idyllic that we even throw in some fun educational stuff too. Let me tell you now this rarely happens. In fact I am not sure I could describe any bath time we have ever had as idyllic. Kid M has an aversion to baths about 80% of the time and kid A much prefers a bath if M is involved too. So most of the time it just involves screaming (hair washes-our neighbours probably think we torture our daughter once a week), crying, bribing and often giving up (me). However occasionally they are fun and everyone enjoys it (I have been trying to work out the magic formula when it does work but I am still none the wiser!).


Anyway when everyone is cooperating we chuck all the bath toys in, and with my oldest try and guess what is going to float or sink. I ask questions so she might be able to try and work out why (what is it made of, what shape is it, is it heavy or light) and get her to think about things we know that float (boats, ducks, beach balls). We sometimes get more logical answers (it isn’t very heavy mummy) and we sometimes get more obscure answers (it’s because it’s orange). However Kid A is interested too and joins in throwing stuff in and squeaking at it. Now he might not be able to respond about items floating or sinking but he is definitely watching and listening to the game. And when something sinks we try and find out where it has gone, so he understands that if it isn’t on top of the water it has gone underneath.

So if you want to test this out at home with your little ones this is what you need:

  • water (essential)
  • container for water (essential – ideally bath but if it’s a lovely day – obviously am thinking back to the sunny summer – then bucket/paddling pool outside works just as well)
  • items to throw in (essential – ideally a mix of ones that float and sink, and things that are ok to be put in water!)


What to do:

  • If you have an older child then you can ask them if they think the item will sink or float before you throw it in.
  • Throw in water and see what happens!
  • If it sinks ask child where it has gone. If it floats then point out that it’s floating. Again if your child is older you can ask them why they think it has done what it’s done, giving them some prompts like “What shape is it? What is it made from?” etc.

Tips/extra bits:

  • Bubbles in the bath make finding the objects that have sunk a bit more fun.
  • Getting your child to throw in the toys while you are running bath/getting things ready for bedtime/tidying up/having a cup of tea is a good activity to keep them busy for 5 minutes. Kid A basically does this every night at bath time now, even when we are not at home (sorry Aunty Sue for everything going in the bath last time we stayed with you!).

The science bit

Am not suggesting you try to explain this to your 1 year old but in case you are interested there are a number of reasons that can cause objects to float on water. There are really tiny objects that don’t even break the surface tension of the water (think pond skaters) or objects that are less dense than water and therefore float (foam bath toys or cork). Finally you have heavy objects, that are more dense than water, that still float (like boats). These don’t always float but when they do it’s because the shape of the object displaces water equal to its weight (this is gravitational pull not how heavy it is). Am going to do some more experiments about objects floating or sinking, and will go into more detail there. Watch this space!


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