Description:
Students investigate whether air is really “empty” by performing an experiment with a cup, paper, and water. They discover that although air cannot be seen, it takes up space and can prevent water from entering the cup.
Intention:
This activity helps students understand that air is matter: it occupies space, even though it is invisible. Students develop their ability to make predictions, observe evidence, and explain scientific phenomena.
Prepare one set of materials for each table group:
1 transparent container or bowl filled with water, 1 transparent drinking glass/cup, 1 sheet of paper or tissue (to crumple) and towels or cloths for spills.
Make a prediction
Before starting, discuss with your group:
- What will happen to the paper if we push the upside-down cup into water?
- Will the paper get wet or stay dry? Explain your prediction.
Here the method Invisible Air can be useful.
Prepare the experiment
- Fill a bowl or container with water.
- Take a small piece of paper and crumple it into a ball.
- Push the paper firmly into the bottom of the cup so it cannot fall out.
- Turn the cup completely upside down. The opening of the cup should face the water.
Test the cup
- Hold the cup straight above the water.
- Slowly push the cup straight down into the water.
- Keep the cup vertical. Do not tilt it.
- Make sure the opening of the cup goes below the water surface.
Check the result
- Slowly lift the cup straight out of the water.
- Turn the cup upright.
- Remove the paper and feel it.
- Is it wet or dry?
Investigate further (optional)
- Repeat the experiment, but this time tilt the cup slightly while it is underwater.
- What do you see happening?
- Where do the bubbles come from?
Explain/discuss
- The cup looked empty, but it was actually filled with air.
- The air took up space and blocked the water from reaching the paper.
- When the air escaped as bubbles, water could enter the cup.
Didactic tips
- Start with predictions. Let students share their ideas before the experiment to make their thinking visible.
- Let students explain first. Ask groups why they think the paper stayed dry before giving the scientific explanation.
- Make the invisible visible. Use the tilted-cup variation to show air escaping as bubbles.
- Connect to daily life. Link the experiment to examples where air takes up space, such as balloons, bubbles, or diving.