Selection of ‘wet’ ideas and activities to explore and promote science-based learning in your classroom.
Transpiration and evaporation
Find a tree or plant that receives a lot of sunlight and has branches that are easily accessible. Place a clear plastic bag over one of its branches (try to pick one that has plenty of leaves), tie it off and leave it for two hours. When you return, what do you observe has happened to the bag?
Just as humans release water vapour when they breathe, so do plants. This process is known as ‘transpiration’. The water is expelled through the leaves of the plant. The plastic bag has trapped the water that would usually evaporate through the plant’s ‘breathing’.
Soft drink bottlewave machine
Fill half a two-litre plastic soft drink bottle with baby oil. Add blue food colouring. Fill the rest with water until it reaches the brim of the bottle. Replace the lid tightly and waterproof it with tape to prevent leaking. What do the students notice has occurred to the water? Place the bottle on its side and gently rock it lengthwise. This should simulate the troughs and crests of a wave.
Fill a jar two-thirds with water. Fill another jar with two-thirds water and add about three tablespoons of salt, stirring until it is dissolved. Add more salt, a small amount at a time, until the water is at saturation point. Gently place an unboiled egg in each jar. Observe and record the results.
The salt water is dense enough to keep the egg afloat, while the opposite is true of the regular tap water. Mention to the students how it is easier to float in the ocean rather than a pool. Why do they think this is the case?
Create simple sailboats using recycled materials and compete in races. Spare balsa wood, used milk cartons, plastic drink bottles, foil etc. can all be used.
Experiment with different materials to find a ‘Flonker’. What is it? A ‘Flonker’ is something that doesn’t float or sink. Float a piece of foam (peanut-shaped, if possible) in a small container of water. What happens? How can you make it ‘flonk’? Try adding things to the foam, like paperclips or pieces of Blu-tack™, to change the weight or shape of the foam. What happens? Keep changing the design until it ‘flonks’ for at least 10 seconds. Record changes and observations.
Float a paperclip! In a cup of water, gently place a paperclip and record what happens. Tear a piece of paper towelling just slightly larger than the paper clip. Gently place the paper towel on top of the water. Place another paper clip gently onto the paper towel. What happens now? Experiment placing the paper clip in other liquids, like soda water, vegetable oil or soapy water to observe and record differences.
Water has a surprising amount of surface tension, as the water molecules ‘hold together’ at the surface. Different liquids have varying degrees of surface tension.
How long can you keep an ice cube before it melts? Get a number of ice cubes and a small box or waterproof container that can hold the cubes. Leave one ice cube as a control and wrap the other cubes in different materials, like aluminium foil, tape, newspaper, rubber bands, plastic wrap or anything you like. Place them inside the container. Wait 30 minutes or any set time. Compare the ice cubes. Which is bigger? Why? What other changes can you make to keep the ice cubes even longer? Try different wrappings, a lid on the container or packing the ice in foam inside the container! Change one thing at a time—predict, observe and record the results.