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We're all used to keeping height measurements for our little ones, but how about something a bit more unusual - here's a great science experiment you can do at bathtime and log growth over time! How large are your toddlers lungs?!
Get hold of a plastic measuring jug (don't be tempted to use a glass jug) and a straw for bathtime. Bendy straws that bend towards one end are perfect for this experiment.
Fill the jug completely with water by submersing it in the bath. Now turn it upside down and slowly lift it out of the water until it is almost completely proud of the water level. You'll notice that pressure keeps the jug full of water even though the column of water rises higher than the water level in the bath. The only way that the water will fall is if you lift the rim of the jug above the water level, at which point the water will cascade out very quickly!
Get the jug to a position where it is filled with water and standing above the water level with the rim still just submerged. Take the straw and place it so that the one end of the straw is under the mouth of the jug with the other out of the water. If you have a 'bendy' straw, bend the end and point the short end up into the jug, and hold the long end clear of the water.
Have your children take a deep breath in and then blow as much air as they can from their lungs into the straw. Younger children may need to practice a bit to master the technique of blowing out fully.
The air blown out will displace the water in the jug and when they are done, you can read off the measurement on the side of the jug to tell the volume of air displaced. Teach older children how to read the quantity by looking at the scale on the side of the jug. You'll be quite surprised at just how much air they can hold! Take a note of measurements and repeat it every couple of months to see how your little ones are growing!