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Science Launch G5 / Week 11 / Wednesday
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Week 11 · Protect Our Planet

Wednesday

Investigation: Build a filter model
// Communities use science to protect resources
⏱ about 15 min

Wednesday: Investigation: Build a filter model

Rocket finally gets to build his filter. A grown-up cuts a plastic bottle in half and turns the top upside down into the bottom.

"Like a funnel," Rocket says. "Now the layers!"

Raven lines up cups of gravel, sand and cotton balls. "Which order?" she asks. "What do you notice about the sizes?"

Nova scans the cups. "Here is a hint," she says. "Big pieces catch big dirt. Tiny grains catch tiny dirt."

Rocket stirs a spoonful of soil into a cup of water. "Muddy creek, ready for testing," he says.

What you need

  • A plastic bottle cut in half by a grown-up
  • Cotton balls or a paper coffee filter
  • Clean sand and small clean pebbles or gravel
  • A cup of water with a spoonful of soil stirred in
Safety first
A grown-up does all the cutting. The cut edge can be sharp, so tape it.
Never drink the filtered water. It is not safe to drink.
Work outdoors or over a sink. Wash your hands when you finish.

Steps

  1. Put the top half of the bottle upside down into the bottom half, like a funnel.
  2. Put a layer of cotton balls in the neck.
  3. Add a layer of sand on top of the cotton.
  4. Add a layer of pebbles on top of the sand.
  5. Make your prediction below.
  6. Slowly pour the muddy water into the top.
  7. Compare the water that drips out with the muddy water you started with.
MAKE A PREDICTION
  • Read the question.
  • Tap your answer.
What do you predict the water will look like after it goes through the filter?
Water sampleColorBits you can see?
Before filtering
After filtering

Real water treatment plants use filters too. Their filters are made of materials such as sand, gravel or charcoal.

But filtering is only one step. Treatment plants also let heavy dirt settle to the bottom. Then they disinfect the water to remove germs.

Your model water may look clearer, but it can still have germs. That is why we never drink it.

What is passing water through layers like sand and gravel called? Type one word.
WHY THIS EXERCISEFiltration removes bits of dirt, and it is one of the steps communities use to clean drinking water.

Model versus real plant

Your filter caught some of the dirt in its layers.

Real treatment plants filter water too, but that is only one step.

They also let heavy dirt settle and then disinfect the water to remove germs.

FILTER THINKING
  • Read the question.
  • Tap your answer.
Why did the pebbles go on top and the sand below?
Why is filtered model water still unsafe to drink?
STEPS AT A WATER TREATMENT PLANT
  • ?Heavy dirt settles to the bottom.
  • ?Water passes through filters of sand, gravel or charcoal.
  • ?The water is disinfected to remove germs.
WHY THIS EXERCISESettling, filtering and disinfecting clean drinking water.

You built and tested a model of a real community tool. Tomorrow we will learn how recycling saves energy.

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