Q1.
Pull the rubber sheet from the centre of the base downwards and watch the balloons (Fig. 9.9a). What do you observe? Now, release the rubber sheet upwards and observe the balloons (Fig. 9.9b). What changes do you see in the balloons?
Answer
When you pull the rubber sheet downwards, the balloons inflate (blow up). When you release the rubber sheet upwards, the balloons deflate (go flat again).
| What you do | What happens to the space in the bottle | What the balloons do | What it stands for in the body |
|---|---|---|---|
| Pull the rubber sheet down [Fig. 9.9(a)] | Space inside the bottle increases | Balloons inflate — air rushes in through the tube | Inhalation |
| Release the rubber sheet up [Fig. 9.9(b)] | Space inside the bottle decreases | Balloons deflate — air is pushed out through the tube | Exhalation |
Why it happens: the bottle is sealed, so the only way air can get in or out is through the tube. Pulling the sheet down makes more room inside the bottle, and air enters through the tube to fill that room — the balloons swell. Letting the sheet snap back reduces the room, and the same air is squeezed out — the balloons collapse. Your chest works in exactly this way.
Check it yourself: if a balloon does not inflate, the seal has leaked. Press the clay round the lid again and check the rubber band at the base — the model works only if the bottle is airtight.