Grade by Grade
C. Matter and Energy · Properties of Liquids and Solids

Soak It Up or Keep It Out

C2.6 A1.2 A1.5 A3.1About 35 minutes
Learning goals
  • I can test materials to see if they absorb water or repel water.
  • I can classify materials as absorbent or water-repellent.
  • I can explain why we choose absorbent or water-repellent materials for different jobs.
  • I can record my results in a chart and share them.

Words to know

absorb
To soak up a liquid. A sponge absorbs water.
absorbent
Able to soak up liquid. Paper towels are absorbent.
repel
To push away. A material that repels water keeps water from soaking in.
water-repellent
Keeps water from soaking in. Drops of water sit on top or roll off.
bead
A small round drop. Water beads up on wax paper.

The spilled juice

Oops! A cup of juice tips over on the table. Quick, grab something! Will you grab a paper towel or a plastic bag?

You would grab the paper towel, because it soaks up liquid. The plastic bag would just push the juice around. Let's find out why.

Remember from Grade 1

In Grade 1 you learned that some materials are absorbent (they soak up water, like a towel) and some are waterproof (they keep water out, like rubber boots).

This year we will use a new science word: repel. A material that repels water pushes it away. Water cannot soak in. Instead, it makes little round beads that sit on top or roll off.

Absorbs water (absorbent)Repels water (water-repellent)
paper towelwax paper
spongeplastic bag
cotton washclothaluminum foil
tissuerubber boot
cotton ballraincoat
breada duck's feathers
Classifying materials by how they act with water

What do they look like?

  • On an absorbent material, a drop of water spreads out and sinks in. The material looks darker and feels wet.
  • On a water-repellent material, a drop of water stays as a round bead on top. If you tip it, the drop rolls off.

Nature's raincoat

Ducks spend a lot of time in water. They spread a special oil from their bodies over their feathers. This helps their feathers repel water, so they stay dry and warm underneath.

Round water drops sitting on the fabric of a red rain jacket.
The water stays in round beads on top of this rain jacket. The jacket's fabric repels water. AI-generated image
paper towelabsorbs:the drop spreads and soaks inwax paperrepels:the drop stays a round bead
The drop test. On an absorbent paper towel, water spreads out and sinks in. On water-repellent wax paper, it stays a round bead on top.
🧽🧻☂️🥾🦆
Sponge and paper towel absorb. Umbrella, rubber boot and duck feathers repel water.

Choosing the right material

People choose materials by what the job needs:

  • To clean up a spill or dry your body, we need absorbent materials: paper towels, sponges, mops, towels, diapers.
  • To keep dry in rain and snow, we need water-repellent materials: raincoats, umbrellas, snow pants, tents, rubber boots and roof shingles.

Some things use both! A winter mitten may have a water-repellent outside to keep snow out and a soft lining inside.

Worked example

Let's do the drop test

Which materials absorb water, and which repel it? We will test a paper towel, wax paper, a cotton sock, aluminum foil and a piece of plastic bag.

  1. Make it fair: Cut each material to about the same size. Put one drop of water on each one, from the same height, using a straw as a dropper.
  2. Predict: I think the paper towel and sock will absorb. I think the wax paper, foil and plastic will repel.
  3. Observe: On the paper towel and sock, the drop spreads out and soaks in. On the wax paper, foil and plastic, the drop stays as a round bead.
  4. Tip test: Tilt the wax paper, foil and plastic. The beads roll off!

Absorbent: paper towel, cotton sock. Water-repellent: wax paper, aluminum foil, plastic bag.

Worked example

Let's choose: A coat for a dog on a rainy walk

Which material is best for the outside of a dog's rain coat: cotton, paper or plastic-coated nylon?

  1. What is the job? Keep the dog dry in the rain.
  2. What property is needed? The outside must repel water.
  3. Cotton absorbs water, so it gets soaked and heavy. Paper absorbs water and tears.
  4. Plastic-coated nylon repels water. Raindrops bead up and roll off.

Plastic-coated nylon is best, because it repels water.

Riddle time

What do you call a duck's raincoat?

Its feathers! Ducks oil them so well that rain just rolls off. No zipper needed.

How to make a straw dropper

Dip a straw into a cup of water. Put your finger tightly over the top. Lift the straw out and hold it over your material. Lift your finger a tiny bit to let out one drop.

Hands-on activity

Drop test lab

You need: a tray, a cup of water, a straw (or eye dropper), and small squares of 6 materials, such as: paper towel, wax paper, aluminum foil, a piece of cotton cloth, a piece of plastic bag, newspaper, a cotton ball, a leaf or a piece of a rain jacket you no longer use.

  1. Make a chart with columns: Material, My prediction, Absorbs or repels?
  2. Predict for each material.
  3. Put one drop of water on each material from the same height.
  4. Watch for 30 seconds. Does the drop soak in or bead up?
  5. Tip each material. Does the drop roll off?
  6. Record your results. Circle the predictions that were right.
  7. Share: Tell a grown-up which material you would use to mop a spill and which you would use to make a tent. Use the words absorb and repel.

Your turn

1

Does a sponge absorb or repel water?

2

Does wax paper absorb or repel water?

3

What does a drop of water look like on a water-repellent material?

4

Which material would you use to wipe up spilled milk: a paper towel or a plastic bag?

5

Why are umbrellas made of water-repellent material?

6

How do ducks keep their feathers from getting soaked?

More practice: warm-up

1

Is a towel absorbent?

2

Does aluminum foil soak up water?

3

Does a cotton ball absorb water?

4

Do rubber boots let water in?

5

What word means "push away"?

More practice: on your own

1

Sort these into absorbent and water-repellent: newspaper, raincoat, tissue, plastic bag.

2

Why are snow pants made with a water-repellent outside?

3

In the drop test, why do we use one drop from the same height on every material?

4

Is a diaper made to absorb or to repel? Explain.

5

You put a drop of water on a leaf and it rolls off. What does that tell you?

Challenge

1

Design a good winter mitten. Which material would you use for the outside and which for the inside? Why?

2

A paper towel company says, "Our towel soaks up the most!" How could you test that fairly against another brand?

3

A sponge floats at first but then sinks lower in the water. Why?

Check your understanding

Quiz

1.

Which material is absorbent?

2.

What does it mean when a material repels water?

3.

Which is the best material for a tent?

4.

On a water-repellent material, a drop of water...

5.

Which would you use to dry your hands?

6.

In a fair drop test, what should be different?

For parents and teachers

Big idea: Materials can be classified by whether they absorb water or repel it (C2.6). We choose absorbent materials for cleaning and drying, and water-repellent materials for keeping dry. This builds on Grade 1's absorbent vs. waterproof.

How to help: Do the drop test at the kitchen table. While getting dressed for snow, ask, "Which parts of your snowsuit repel water? Why?"

Communicating results (A1.5): Encourage a simple chart and a sentence using "absorb" or "repel".

Common difficulties:

  • Mixing up absorb and repel. Link "absorb" to a sponge soaking up and "repel" to rain rolling off an umbrella.
  • Thinking an object can only be one thing. Many products (mittens, diapers) use layers that do different jobs.

Safety: Water on the floor is slippery. Do the lab on a tray and wipe up spills.