Why kids think air is nothing
Ask a 5-year-old what is inside an empty cup and you will hear "nothing." Fair enough: air has no color, you cannot hold it, and you only notice it when the wind blows.
Scientists disagree. DK's 1000 Words STEM puts air on its materials page, next to the word gases2. Isabelle and Zinn's STEPS to STEM, a curriculum for upper elementary and middle school, explains that gases are made of particles too small to see, moving freely, and that this explains the shape of a balloon1.
An empty cup is not empty. It is full of air, and tonight your child can prove it.
The two big ideas, in parent words
Two sentences explain every experiment below. Say them first, then let the experiments convince.
| Big idea | What is really happening | Say it like this |
|---|---|---|
| Air takes up space | Two things cannot be in the same place at the same time. Air must leave before water can move in1. | "The cup is already full of air." |
| Air pushes | Pressure is tiny particles bumping into a surface. Pack more into the same space and the push grows1. | "Squeezed air pushes on whatever is in its way." |
The invisible gas all around us. It is made of tiny bits too small to see12.
Say it: “Is this cup empty, or full of something we cannot see?”Stuff with no shape of its own that spreads out until it fills the space it is in, like air12.
Say it: “What happens to the air when we blow up a balloon?”A push or a pull2.
Say it: “Can air push? Let's find out.”How hard air (or water) is pushing on something1.
Say it: “Where is the air pushing harder, inside the balloon or outside?”Experiment 1: the paper that stays dry underwater
The quickest proof that air takes up space. It is our adaptation of a rule from STEPS to STEM: two things cannot be in the same place at the same time1.
Dry paper in an upside-down cup
- 1 clear plastic cup
- 1 paper towel
- A big bowl or sink of cold water
- Crumple the paper towel into the bottom of the cup. Flip the cup to check it stays put.
- Ask: "If we push this cup under water, will the paper get wet?"
- Hold the cup straight upside down and push it straight down under the water.
- Count to five, lift it straight up, and feel the paper.
- Repeat, but tilt the cup under water. Watch the bubbles, then check the paper.
Experiment 2: the balloon rocket on a string
Now show that air pushes. STEPS to STEM poses this as a team challenge: what design makes a balloon rocket travel the farthest1? The string-and-straw setup is our adaptation.
Balloon rocket down the hallway
- 1 balloon
- 1 drinking straw
- About 13 feet of string
- Masking tape
- 2 chairs
- Thread the string through the straw. Tie the ends to two chairs, pulled tight.
- An adult blows up the balloon and pinches the neck. Do not tie it.
- Tape the balloon to the straw, neck pointing at one chair.
- Ask: "Which way will it go?" Then let go.
- Measure the distance: steps for ages 5-7, a tape measure for ages 8-10.
- Change one thing per run (more air, a different balloon) and race again.
The book lists the rule among its standards: when two things push on each other, the pushes are equal in strength and opposite in direction1. Air rushes out the back, so the balloon zooms forward.
Experiment 3: blow into the bottle, watch the paper come out
A real surprise, from the Which Way? activity in STEPS to STEM1.
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01Lay an empty plastic bottle on its side.
The book uses a soda bottle1.
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02Put a small wad of paper in the neck.
Just inside the opening1.
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03Ask for a prediction.
"If you blow across the opening, will the paper go in, come out, or go straight up?"1
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04Blow hard across the opening.
Not into it. Keep your mouth level with the bottle1.
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05Talk about it.
"Did it do what you predicted?"
Air pressure at the opening is lower than inside the bottle1
In plain words: fast-moving air spends its push going forward, so it presses less on its sides1. Your breath lowers the pressure at the opening, the still air inside pushes harder, and the paper is shoved out toward you1. The book's point is the surprise itself: when the world does not act the way we expect, scientists have a puzzle to explain1.
Experiment 4: how much air is in one breath?
For ages 8-10, this STEPS to STEM activity measures air by watching it push water out of the way1.
Measure a breath with a jar of water
- A large clear plastic jar with a lid
- A measuring cup and a marker
- A sink with a few inches of water
- 2 or 3 bendy straws taped end to end (the book uses rubber tubing)
- Make a scale: pour in 8 oz of water and mark the level. Repeat to the top1.
- Fill the jar, cap it, and turn it upside down in the sink, opening under water1.
- Unscrew the lid under water, tip the jar slightly, and slip in one end of the straw1.
- Take a deep breath and breathe out steadily through the straw1.
- Read how many ounces your breath pushed out. Do it 3 times and average1.
- One straw per person. An adult stays at the sink.
The entering air forces out the water in an equal amount.1
Common mix-ups, and how to talk about them
An empty cup has nothing in it.
Blowing always pushes things away from you.
Fast-moving air presses less on its sides, so still air can push things into the stream, like the paper ball coming out of the bottle1.
Can: See and feel results: a dry towel, a zooming balloon, a paper wad that pops out. Use the words push, pull and air2.
Try: Run Experiments 1 to 3 as magic tricks. After each, ask: "What did the air do?"
Can: Measure, repeat and average, and explain with the words pressure and compress1.
Try: Add Experiment 4, and run the balloon rocket as a fair test with a tape measure.
- Cup, paper towel, bowl of water
- Balloon, straw, string, tape
- Plastic bottle, scrap of paper
- Plastic jar, measuring cup, straws (ages 8-10)
- A towel for splashes
If you want a kit for this
Everything above works with what is in your kitchen. If your child wants to design their own launch tracks and test rigs, our STEM Cardboard Construction Kit is a good next step.
Build it with / Ages 5-7STEM Cardboard Construction KitKid-safe tools turn any box into a machine.$44.99GoP Toys sells the kit mentioned above. None of the sources cited tested our products.