Making a sand timer

The small boy is currently keen on things to do with measurement and time. He's not really got the hang of time at all - he now knows the order of the days of the week, and can read the clock if it's exactly on an hour (and sometimes half past or quarter to/past) but everything else is still a middle. To try and focus on seconds and minutes I thought we could combine a bit of building/experimenting with counting seconds.

He's seen sand timers before, but I thought he might enjoy making a big one. We tried a simple design which I hoped would be quick to construct and therefore fit with a 3 year old attention span.  It didn't end up being as quick and straightforward as I had envisaged but I'd learn from the problems we encountered if I did it again!

The basic idea was to connect two plastic bottles via a bottle cap with a hole in it. Before starting, I picked two identical 500ml bottles. The ones I chose were the only ones I had two of, but if you have a better choice in your cupboard, go for smaller volume and those that are short and wide rather than tall and narrow to make the finished sand timer more stable.

The next step was to put a hole in the bottle top. Again I did this before starting and I wasn't sure what size hole I would need. I went for about 2mm, but this turned out to be too small...

The equipment we needed (aside from the drill...)

With the small boy, I stuck the bottle cap with a hole onto one bottle, the wrong way up. Beware with small children and hot glue - he 'helped' by pushing the glue stick in and I kept his hands away from the hot bit. We stuck it firmly but in the end this is where the sand timer broke as it is the weak point. You might want to strengthen the joint with some tape, depending on the clumsiness of your children!

Filling the sand timer

The next step was to scoop in some sand. This was nearly another problem, but I realised sufficiently far before we started to rectify it - our bag of play sand was damp so the sand clumped together. Thankfully the oven was still warm from earlier baking so I stuck some on a tray in a thin layer to dry out! It definitely needs to be dry or the sand will keep getting stuck in your sand timer.  Learning from my mistake when we were experimenting with granular segregation of coloured rice and pasta, we used a funnel to help my son scoop the sand into the bottle without the cap stuck on.

Timing how long the sand took

I let him scoop in as much as he wanted, and then we screwed the sand-filled bottle onto the other one, tipped it up and... nothing happened.  He was bemused, and I realised why I often test activities on my own first to make sure they work.  Not to be deterred, I decided it wouldn't be such a bad thing for him to be involved in working out what the problem was and fixing it.  I asked him why he thought the sand wasn't going into the bottom bottle, and he thought maybe the hole wasn't big enough, which was my diagnosis of the problem too.  Then I asked him how we could make it bigger and his eyes lit up as he told me we needed a power drill, so I got it out.

I decided to go for making the hole a little bigger, as I didn't want all the sand to go though quickly, but actually it needed making a lot bigger.  I don't really know why as little sand timers seem to work ok with a small hole and the play sand seems really fine.  Anyway, we ended up drilling the hole with drill bits of increasing sizes, testing it, and drilling again until we got it to work with an 8mm hole.  He thoroughly enjoyed the first few iterations, but was getting a bit twitchy by the time I got it to work.

With the hole of a functioning size, we then used his watch - which he's really quite proud of, even though he struggles to read it - to time how long the sand took to go through.  It was just under 20 seconds, so I suggested that we add more sand to see if we could make it time one minute.  I'd wanted to use the opportunity to reinforce the fact that there are 60 seconds in a minute, and get us to count to 60 and watch the second hand go all the way around.  However, when he added his chosen amount of extra sand, we timed it and it was only 32 seconds.  I suggested adding more and getting closer to a minute, but he said it was fine as it was and he was finished.  Oh well.

We talked later about minutes having 60 seconds and watched the second hand go around on our wall clock, without reference to the sand time.  However, he was proud of his sand timer and wanted to show it to Daddy when he came home from work.  But then disaster struck and when he tried to turn it over slightly clumsily it snapped in the middle at the glued joint and we got sand all over the floor.  Oops!

So if I was to do this again, I'd reinforce that middle joint with some tape to try and avert a similar sand disaster inside the house.  In summer, I'd do the whole thing outside as his scooping of sand, even over a box to contain it, wasn't 100% accurate either so we ended up cleaning the floor twice in one day to get rid of the sand.  I would also use a shorter, stouter bottle at each end as the whole thing was a bit wobbly and top-heavy when turned upside down by 3 year old hands.  Still, he had some fun and we talked a little about time, even if it didn't work perfectly and we didn't make the minute timer I had in mind when we started!