Exploring weights

I've been thinking about how to introduce the small boy to measuring things, and this week's theme for #mathmondayfun on Instagram is 'discovering weight' so I thought we'd have a go at a weight-related activity.  By 'weight', I really mean 'mass' i.e. the thing you measure in grams/kilograms (weight is about the force something with mass exerts due to gravity, and is measured in Newtons), but as I have a three year old, and people usually say things like 'how much do you weigh' and expect an answer in kilograms (or pounds if they're above a certain age), then I've not introduced this distinction now. 

I thought I'd start out by trying to find out what the small boy already knew about weight as I wasn't quite sure what he'd already picked up.  I set out eight household objects which I'd already weighed, ranging from 5g to 1kg, and invited him to pick them up in pairs, one in each hand, and tell me which one was heavier.  He immediately understood what he'd been asked to do, and picked up two very different objects (a bottle of water and a silicone cupcake case) and told me correctly which was heavier.  

I asked him to swap one of them for something else (a tub of bicarbonate of soda) and asked him which one weighed more.  He wasn't sure, and after a bit of conversation and picking up other objects, it turned out that he could tell which was heavier (they were about 500g and 200g), but he didn't understand what 'weighs more' meant.  He had a clear grasp of 'heavier' and 'lighter' but not use of phrases about 'weight'.  However, once I'd explained what the words meant, he was happy to proceed with testing pairs of objects and lining them up in order of 'weight' ('heaviness' as he called it).  In hindsight, eight objects was probably a couple too many, but he stuck with it.  I'd chosen the objects to have a spread over the weight range, but to have two around 200g, with larger one being lighter, and he placed these the wrong way around (which I thought might happen).

Objects arranged (mostly) in order of ascending weight from left to right

For the second part of the activity, I'd written the object weights in grams on some pieces of cardboard.  The word 'grams' wasn't new to him as he knows this is what we use when we are baking (well, unless I'm making a recipe I know which is in pounds and ounces...), but I took the time to explain that grams are what we measure weight in, and that we needed to match the objects to the number of grams that they weighed.  I'm not totally sure that he understood, but he tried to decipher the numbers and we talked about which were bigger numbers and which were smaller, and lined the numbers up against the objects.  Again, there were a few too many as he had spotted my old scales on the table and wanted to investigated them rather than trying to read the bigger numbers.

We moved quickly onto part three of the activity, which was checking the weights on the scales to see if he had guessed correctly.  The scales are my old ones from university which are pretty inaccurate, but are nicely visual - there's a big dial with a needle, and they measure from 0-1000g (i.e. 1kg) with markings every 10g. 

He was intrigued by the scales, and we started off weighing the heaviest object to see if it was correct.  This was a 1kg bag of sugar and the dial on the scales went all the way round and back to the top. Next he chose to weigh the lightest three which were 5g, 10g and 100g; he was able to read these on the scales with a little help (the 5g being half way between zero and 10 which we talked about by using our fingers to count to 10 and checked that 5 is in the middle). 

Eventually he checked the weight of the bicarbonate of soda and found it was over 200g, but the baby rice which was next was actually 200g; these was the ones that were misplaced and we discussed how the bigger tub (baby rice) actually weighed less than the smaller one despite looking bigger.

Weighing a kilogram of sugar

After he'd weighed all of the objects (not all in order), he went back and re-weighed most of them several times.  I'd not foreseen this part of the activity, but he enjoyed weighing things together then taking one of them off and seeing what happened.  I suspect he may have learnt most from his own investigations - it certainly occupied him for more time than I'd thought it might.

I suspect he's gained a bit more understanding of weight and the language we use to describe it, and has a better idea of how we can use numbers to measure how heavy things are.  I doubt he's grasped the idea of units of measurement, but I think we'll come back to something weight-related soon as he liked using the scales and I'm sure he'll learn a little more each time he weighs things.