Outdoors: Stem – floating and sinking

quick wins – float or sink challenge

Challenge children to predict whether the object will float or sinkin a trough of water using what they find in the garden. Encourage them to explore and examine each object, describing it with STEM words (e.g. heavy, light, soft, bouncy, hollow, hard) before placing it into the water. Use polystyrene packing material or pieces of cork tile to enable children to test what happens when objects that did sink now don’t sink when placed on top of the polystyrene or cork.

Why do some of the objects float and others don’t? Buoyancy is the force that pushes an object upwards when it is in a liquid. Children can feel this force if they try to make a very buoyant object sink – push a bouncy ball or a cork down into the water and feel the resistance. Objects sink or float depending on their weight, shape and density. A ‘dense’ object is heavy and solid for its size, such as a ball bearing, so it sinks. The same amount of metal in a sheet will float because it is less dense and the weight is spread over a larger area.

Source a ceramic ornament and a small saucer of similar weight, or a plastic fork and a metal fork of similar size. Weigh and measure them, then predict and test which will sink or float.

An object that floats in a tuff tray or trough might not ‘float’ in a puddle – why?

in the moment – the scientific method

Buoyancy experiments offer an excellent opportunity to develop children’s STEM language and experimental skills. Applying the ‘scientific method’, using age- and stage-appropriate words and examples, will help them make sense of complicated concepts. When children are playing in the water trough, use the moment to introduce some of this language and methodology:

1 Define a question – for example, will this plastic beaker float?

2 Make predictions – yes it will/no it won’t/it depends on which way round we place it in the water.

3 Gather data – place the beaker on the water in different positions and watch what happens each time.

4 Analyse the data – discuss what happened.

5 Draw conclusions – why did the beaker sometimes float and sometimes fill with water and sink?

Light and hollow objects, such as a beaker, will float because they spread their weight over a large area and contain air, which is less dense than water. However, if the beaker is placed on the water upside down, it will tip over and water will flow into it. It is now ‘dense’ and not hollow so it will sink.

Ships float because their weight is spread over a large area; if water gets into the ship’s hull (which should be full of air), it will sink.

Submarines have to fill special ‘ballast’ tanks with water in order to sink, and release it when they want to resurface.

Have children tried floating at the swimming pool? If they spread their bodies out, they may be able to float; if they curl up into a tight ball, they will sink.

continuous provision – sink or sail?

Access to water outdoors is a crucial element in any setting. Pretty much the first thing we say to settings when we arrive to help them shape their outdoor spaces is ‘where is the tap?’ If you don’t already have an easily accessible outdoor tap, installing one is inexpensive and will transform water play (and gardening) outdoors.

This month’s ideas are focused on helping you understand and introduce STEM language and methodology to water-play fun.

Transparent containers to allow children to observe the behaviour of objects, including tubs, tall test tubes (the ones that come with bubbles in are useful), bottles and, if possible, a large transparent trough – ideally on legs or a frame so that children can get underneath it, as well as around and above it.

Encourage children to experiment with the resources you already have outdoors – toys, blocks, natural materials.

Oil – for experiments with layers, buoyancy and density.

Food colouring – makes some experiments easier to observe.

Tools and equipment of various sizes to encourage controlled manipulative movements: spoons, scoops and ladles, droppers, tongs, sieves and tea strainers, slotted spoons, clear measuring jugs, a set of measuring spoons or cups, pipettes (the ones from liquid paracetamol are ideal).

Role-play resources: lifeboat station; underwater explorer; fishing or fishing boats. If parents could donate a few ‘shorty’ wetsuits, they are huge fun to play in, especially when coupled with snorkel sets. Make ‘oxygen tanks’ from painted or covered bottles and ‘flippers’ from sturdy cardboard.

Claim a corner of your freezer so that you always have some ice set aside for STEM play – ice cubes of various shapes as well as plastic food bags filled with water to make very large chunks of ice.

Enhancement –

Not every liquid has the same density as water: vegetable oil, honey or syrup, and very salty water offer a good starting point. A selection of science (and cooking) equipment will enhance experimentation.

Bottle Babies: fill 1l and 2l drinks bottles with water, or a mixture of 80% water, 20% oil. Add food colouring (which will mix with the water but not the oil) or small objects and seal the lids so they can’t be opened again.

Curate a set of resources that will allow children to make boats – cork tiles, chunks of bark, skewers, Blu Tak or plasticine, egg boxes, pieces of fabric, small food cartons, etc. Choose ‘hull’ building objects of various weights to give children the challenge of deciding on suitable materials depending on the criteria.

Floating and sinking in the air: keep a few bottles of bubbles and some balloons. The bubbles float upwards and are buffeted by the wind; balloons, unless filled with helium, will sink.

resources

In Mr Archimedes’ Bath by Pamela Allen, Mr Archimedes can’t understand why his bath overflows when his animal friends climb in with him. It’s quite an old book now, but there are video readings on YouTube and it remains a simple and entertaining explanation of the principle.

The Bucket List Family (on YouTube) have a video of their five-year-olds watching fish and sharks from a shark cage – watch from around20:30-22:15 to see them breathing underwater with fish swimming around them and sharks nearby. The voiceover and music prevent it from being frightening, and there are a shots of the boy bouncing up and sinking in the cage.

planning ahead

To help children think about density and volume, weigh a level tablespoon of honey and one of water. Objects of the same size (or volume) usually don’t weigh exactly the same.

Three-quarters fill a tall jar with water, then fill a pipette or dropper with oil. Plunge the pipette into the water and release the oil – then watch it float back to the top. If you keep adding oil, a layer will form at the top.

Icebergs: fill five or six bags (of various sizes) with water – seal the tops tightly and fit them into the freezer amongst other items so that they freeze into interesting shaped ‘icebergs’. Also freeze a few regular sized blocks in ice cube trays and food cartons. Fill a deep outdoor trough with water and give children the icebergs to release into the trough. Observations might include: how much of the iceberg is below the water; why ‘water’ is floating on water; does the shape of the iceberg make a difference to its buoyancy?; which icebergs will melt quickest?

Glossary: Float, sink, buoyant, air, water, Weight, light, heavy, dense, Sail, swim, paddle, drift