Measuring temperature

The small boy has previously enjoyed experimenting with melting big ice cubes in warm and cold water, and has a good idea of what 'hot' and 'cold' mean, but I thought it'd be nice to introduce the idea of measuring temperature, and to have a play with a thermometer.

I set up some plastic beakers of water of different temperatures ranging from hot water out of the tap to frozen (with a little salt added). The beakers were coloured and I tried not to arrange it so the warmer temperatures were in the colours we usually associate with warmth. 

The first thing I asked the small boy to do was to feel the beakers and put them in order of temperature i.e. to put them in a line from hot to cold, or vice versa. I didn't give him a thermometer, so - after checking with me if any were too hot to touch - he stuck his fingers into the water and felt each one. One was visibly frozen, and he correctly identified this as the coldest. He had no problem finding the hottest either, and did a few comparisons of the ones in the middle before getting them in the right order. This was a similar thought process to an activity we did a while ago with weights of kitchen objects where he arranged by weight using his hands and then checked with scales.

Feeling the temperature of beakers of water

I then asked him what we could use to check the temperatures. He knew he needed a thermometer - there's one in his pretend doctor's set which he uses to 'measure' my temperature and decide if I need 'medicine'!  I produced a thermometer he hadn't seen before - it's made of glass, so I explained that we needed to handle it gently to avoid breaking it.

We had a look at the thermometer together, and he could see the red line in the middle and the numbers printed on it. I drew a thermometer and we talked about what the numbers meant - they are how we measure temperature in units called degrees Celsius. He knows that we measure distance in centimetres and weight in grams, so this wasn't a totally strange concept. We had a look at what number the thermometer was on and then he held the bulb of the thermometer in his hand and watched the red move up the thermometer. I helped him to read the temperature and then suggested he measured the temperature of each beaker of water.

Looking at how the thermometer shows temperature

He was a little impatient with letting the thermometer warm up to the temperature of the warmest cup, so his measurement was probably not accurate, but otherwise he told me which 10s (which are printed on the thermometer) the line was between and then I helped him count the smaller divisions to give the temperature reading. We marked them on my drawing of a thermometer using a felt tip pen which colour matched the beaker, and showed that the order of temperatures matched the order he'd put the beakers in based on how hot or cold he thought they felt.

Measuring the temperature of water with a thermometer

The frozen one, which had some salt in it, was slushy enough to put the thermometer in and he noticed that it read below zero. I wasn't sure whether I'd made the right choice by putting salt in to lower the freezing point but he was really excited to discover that there are numbers below zero (negative numbers)! We discussed how water freezes at zero degrees (he kept missing the word Celsius but he's 3 and it was the first time we'd talked about units we use to measure temperature) and that our freezer can make things colder than that.

I also arranged our Alphablock letters to spell out 'hot' and 'cold'.  He spontaneously sounded these out when he saw them on some taps a while ago and I wanted to give him another chance to try and read them. He enjoyed being able to read the words, and putting them in the right place both against the thermometer and next to the beakers of water.

I wasn't sure quite how much he'd learnt from this activity, but he's since talked about water freezing at zero degrees and told me what the numbers on our oven mean.  I've also started talking about the temperature the weather forecast says it is going to be on a given day, and he often asks me (usually because he wants to put our little paddling pool out); he knows that it's going to be a warm day if I say it is forecast to be 20 degrees Celsius or higher.