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Age group 3rd – 6th class
Total time: 1hr
Outline: To learn about the importance of water, the water cycle and how to make a water filter
|Links to Primary Curriculum||Key Learning points|
– recognise that materials can be in solid, liquid or gas form (Science, Materials )
– identify and investigate a widening range of common materials in the immediate environment water, air, rock, fabric, paper, metal, wood,plastic, food (Science, Materials )
– begin to use simple methods to estimate, measure and compare observations (Science, Estimating and measuring, 1st-2nd class)
– estimate and use appropriate units of measurement (Science, Estimating and measuring, 5th-6th class)
|– All life forms are mainly made up of water and need water to survive|
– The main stages of the natural water cycle are all physical processes
– The pore size of a material controls its filtering capacity
Notes for parents/carers and teachers
This activity can be carried out at home by a child/small group of children and an adult, by varying the types of age-appropriate tasks. The materials are available at home or easily obtainable. The activity is written out with instructions directed to the child’s parent/carer. Feel free to adapt this activity as appropriate.
1. Water water everywhere….
NOTE: For younger children, feel free to carry out the experiment first and then ask them some questions about what they think happened after.
Brainstorm on the story of water and its natural cycles
Start with saying something like….We use water for so many things at home and at school. (Can you name a few?) Have you ever thought about what happens to water before it reaches your tap, and after it leaves your drain? How many different things do we mix in with our precious water which then goes down the drain? Do you know that water is used to make your clothes, your books, and even your toys! Let’s read on and find out more about water.
After discussing the questions above, you can read the following together…
Water is essential for life. It exists everywhere in our Solar System, and it was part of the Earth from its formation. Physics helps us measure properties of water like its temperature, pressure, and its buoyancy. Physics helps us see the relationship between these. For example physics can help us create a picture or a graph of what happens to a cup of water if it is heated (its temperature increases) over a set time.
Our bodies and those of all species are mostly made up of water. Life began in the oceans and then gradually evolved to live on the land. 70% of the Earth’s surface is covered in water, but only 2% of it is fresh water which we can drink and use to grow food with. So we really need to protect it. Clean water is crucial for every living thing to be able to live a healthy happy life, but we humans sometimes waste and contaminate this precious resource.
Remember all the things you just named, which we use water for in our homes? (toilets, washing machines, dishes, cooking, bathing etc). In Ireland we use about 133 litres of tap water per person per day. But how much really is that? Most people buy milk in one litre or two litres cartons. Take a litre of milk from your fridge if you have one. Imagine how much space 133 litres of milk would take up in your kitchen? Can you calculate how much water your whole family roughly uses in a week?
Apart from the tap water we use in our homes, almost everything we buy needs water to make it. Factories use huge amounts of water to make everything from toys to clothes and cars; they all use water to manufacture them.
We all want clean water in our taps, but its getting harder to make sure we all have it for many reasons. Did you know that already about 1.2 billion people around the world don’t have access to clean water? That’s 1/6 of the world’s population.
It’s up to all of us to reduce the amount of water we use. Buying less stuff is an important way to reduce the water we consume. For example it takes 1358 litres of water to make a cotton tshirt between growing the cotton plants, manufacturing the fabric, dying it, transporting it etc. Using our rainwater is another great way, because we sure have enough rain in Ireland. So let’s put it to good use!
Rainwater harvesting means collecting our rainwater from our roof tops in different sized containers or tanks, to use in our homes, schools or work places. This water can be used for the garden, washing machines, toilets and much more. This water may need to be cleaned by filtering because it can get dirty from sliding off your roof and down the drain pipes into the rain butt (a large barrel for collecting rain water). Let’s experiment by making a simple water filter to clean some dirty water and find out which materials work best.
Feel free to add these interesting facts into the conversation.
Did you know?
- The human body is between 60% and 70% water
- It takes 24,000 L of water to produce 1Kg of chocolate. This is called the hidden water use.
- The food you eat makes up the largest part of your overall water footprint – about two-thirds (Your water footprint is the amount of tap water you use as well as the ‘virtual water’ used to make your food, electricity, petrol, clothes, toys etc). The more processed foods, meat and dairy we eat, the more water we consume. So eat more fresh fruit and veg to save water!
The Water Cycle
The water cycle is a marvelous physical process which recycles all the planet’s water continuously. Physics is very important in the water cycle, because it helps us understand what happens when the temperature and pressure of the water changes.
- First, water on the surface of the Earth evaporates. Liquid water becomes a gas because the sun gently heats it.
- Then, water collects as water vapour in the sky. This makes clouds.
- Next, the water in the clouds gets cold. This makes it become tiny droplets. This process is called condensation.We’ve all seen condensation on our windows when they fog up.
- Then, the water falls from the sky as rain, hail, sleet or snow. This is called precipitation. The tiny droplets join together and become liquid water again or even frozen water like hail or snow.
- The water sinks into the earth’s surface and also collects into lakes, oceans, or aquifers. As it travels down through all the layers of soil, sand, gravel, and bedrock, the water is cleaned or filtered because the dirty particles get trapped in the different layers.
As we put more chemicals and rubbish in our water supply, this natural cycle can’t clean the water entirely anymore, and those contaminants are accumulating in certain places like lakes and oceans and the soil. You probably know that we have sewage treatment plants which clean up some of our dirty waters, but they can’t clean all of our water.
2. Making our own water filter
What you need
Use reused/recycled materials where possible (plastic bottles,old clothes )
Two water bottles (1L – 2L), scissors or knife, fabric (e.g. old sock), or cotton balls, sand and/or charcoal (from campfire or BBQ, not instant type which is soaked in chemicals), gravel, large gravel or small stones,cup to hold filtered and non-filtered water/ cut-off base of water bottle, mucky water!
1) Using your scissors or knife, cut off the very end of the two water bottles
2) Using your knife, scissors, or anything sharp (nail), make a small hole in the centre of each lid. Make sure the lids are on tight!
3) Stick the fabric (or cotton balls) down by the lid. (Hint: Use tightly woven fabric for better filtration)
4) If using charcoal, crush it by first placing it in a strong plastic bag and breaking it with a hammer or rock, making it into quite a fine powder.
4) Now fill one bottle with about 6-8cm of sand and the other with 6-8cm of charcoal.
5) Next, add your gravel into each bottle. Around 6-8cm of gravel should be enough.
6) Finally add your larger gravel or small stones into the bottle. Again, 6-8cm is enough. Your water filter is now complete!
7. Just put the filter over your cup for filtered water. With the other cup, pour the dirty/muddy water into the filter. Pour the water slowly to minimise disruption to the different layers in your filter.
8) Observe the difference in colour, and maybe smell, of the two samples of filtered water that you end up with from the two slightly different filtering materials.
3. How does my water filter work?
Prompt the children with some questions like these below. You can then read the full explanation to them, or better still, put it into your own words.
How do you think the different layers in the filter work to take the dirt out of the water? What do the stones and gravel do? What does the sand or the charcoal do? What does the fabric/cotton do? Why do you think we put them in this order with the smallest sand/charcoal particles at the bottom, and biggest stones/gravel at the top?
There is lots of everyday physics behind the cleaning of water. One way to clean water is by filtration. When water is being filtered, we need to use the right materials to do the job. These materials usually have very tiny holes or ‘pores’ that allow the water through, but stop or trap the dirt. We need to have the right size of pores, so the filtering material will remove as much dirt or impurities as possible from the water. When the water first travels through the stones or larger gravel, the bigger particles that are suspended in it, like leaves or twigs, get caught in between them and so the cleaning begins. The water keeps seeping down through the next layer of gravel which catches some smaller particles, like tiny stones or bits of grass. As it continues downward smaller and smaller particles or pieces of dirt, get caught in between the smaller particles of sand/charcoal, until eventually the fabric/cotton catches the tiniest particles of all, and the water comes out much more transparent than the muddy water that went in.
This is a good example of a basic water filter, but we can’t get fully clean water from it. Some dirt actually dissolves completely in the water and isn’t easily taken out with these physical filters. Chemical filters are used in water treatment plants to help remove the final dirt in the water, as well as kill nasty bacteria. That’s why your filtered water from this experiment is not drinkable, even if it’s a lot cleaner that it was before.
4. What did you like? What did you learn?
What did you like most about making this water filter?
What did you learn about water and conserving it?
What else would you like to try if you did this experiment again?
5. Elisa Palazzi’s passion for protecting the planet
Inspired by her maths and physics Professor in secondary school, Elisa Palazzi decided to study Physics at the University of Bologna. After completing her Bachelor of Science, she continued on at the same University and in 2008, completed her PhD in Physical Modelling for Environmental Protection.
Elisa’s career in climate change began at the Italian National Research Council (CNR) in Torino, Italy. After moving to a new research group that focused on the mountain environments, Elisa found her passion. The work was exciting: she enjoyed researching mountains, how important they are in providing essential services, such as water, and how sensitive they are to climate and environmental changes.
Elisa’s advice for female professionals embarking on a career in science is to be self-confident and not feel inadequate. The key to success, according to Elisa, is a mix of study and dedication, open-mindedness, curiosity, asking questions and the ability to change one’s mind. This is a never-ending process.
6. Extra Resources