Sinking and floating in a bottle

Following on from the fun I had with my smallest son playing with a large box of water and whether food and spoons sank or floated, I wanted to try something a bit quicker and less wet for when I can't devote all my attention to him for long.  I thought we could try investigating whether things floated or sank in a clear plastic bottle with a screw on lid.

The idea was to find some materials that sink, and some that float, such that he can observe what happens.  In a bottle with a tightly closed lid (he can't yet undo them) he can then turn the bottle upside down and watch what happens to the objects.

I needed a bottle with a big enough neck to take objects which aren't choking hazards, and a selection of things with varying buoyancy in water.  I ended up with a Duplo brick, the Numicon shape for 2, a wooden block and a wooden lolly stick, a plastic clip, a metal teaspoon, a ball of aluminium foil, a key and a ball of cotton wool.

The very small boy had fun putting the objects in the bottle.  He's just getting the hang of a simple shape sorter and he seemed to like being able to see where things had gone.  He pointed at some of them after they'd gone in, and seemed to notice that some stayed at the top and others sank to the bottom.  He was particularly interested in the cotton wool ball, which initially floated and then sank as it soaked up water.  He's not sufficiently coordinated yet for me to take my hands off the bottle for long though, so I held it most of the time to prevent spills.

Putting the objects in the bottle

Once he'd put the objects inside, I put the lid on.  He wasn't happy about it to start with, and had a bit of a grumble, but once I showed him that he could tip it upside down, he cheered up again.  He found tipping it a bit tricky as it was quite heavy (about 1kg), but he found he could have fun rolling it.  He was definitely interested in where the objects were inside, and played for long enough for me to help his brother with something else; he's pretty clingy at the moment, so I counted this as a successful variation on the theme of sinking and floating.

Experimenting with rolling the bottle (it was rolled a long way across the floor after this)

Pointing at things inside the bottle