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NCERT Solutions for Class 5th The World Around Us Chapter 7 The balloon, and the Balloon Air Rocket — Activity 1

Book page 116 Updated on2026-09-19

Q1.
1. Take a balloon and blow into it until it fills up. 2. Hold it tightly. 3. Then, release the mouth of the balloon and observe what happens.
Answer

What you will see: the moment you let go, the balloon shoots away across the room. It flies about in a wobbly, twisting path, making a hissing sound, and it drops down only when all the air has come out.

How to do it:

  1. Blow air into the balloon until it is nicely full. Do not fill it so much that it may burst.
  2. Pinch the neck tightly between your thumb and finger. Hold it up, away from your face.
  3. Now open your fingers — but do not throw the balloon. Just let it go.
  4. Watch which way it flies, and listen to the sound.
What I watchedWhat I observed
The airIt rushes out of the neck in a fast stream. You can feel it if you hold your palm near.
The balloonIt flies off in the opposite direction to the escaping air.
Its pathNot straight — it twists and turns, because the neck keeps flapping about.
The soundA hiss or a squeal, made by the air pushing through the narrow neck.
The endWhen the air is finished, the balloon is limp and it falls to the floor.
Why it happens: When you blow into the balloon you squeeze a lot of air into a small space. The stretched rubber presses on that air. The moment you open the neck, the air rushes out. As the air rushes backwards, it pushes the balloon forwards. In the book's words — when air rushes out of the balloon, it pushes the balloon forward. This is how the movement of air generates energy.
Feel it yourself: Blow up the balloon again and hold it near your cheek before you let go. When you release it, you feel the air on your skin. That moving air is doing the pushing.
Q2.
Extension Activity: Balloon Air Rocket — 1. Fill the balloon with air and attach it to a straw with tape. 2. Pass a string through the straw. 3. Hold the ends of string with someone's help. 4. Now, release the balloon and watch it move along the string.
Answer

What you will see: the balloon zooms along the string from one end to the other, carrying the straw with it. This time it does not wobble about, because the string keeps it going straight.

How to make it:

  1. Cut a drinking straw to about half its length.
  2. Thread a long string (3 to 5 metres) through the straw.
  3. Tie or hold the two ends of the string tight, across the room. Ask a friend to hold one end.
  4. Blow up the balloon. Pinch the neck so the air cannot escape.
  5. With your other hand, stick the balloon to the straw with two strips of tape, with the neck pointing backwards.
  6. Slide the straw to one end of the string. Check that the string is pulled tight.
  7. Let go of the neck.
String held tight Straw Tape holds the balloon to the straw Air rushes out this way Rocket flies this way
The air goes one way, the balloon goes the other way — and the string keeps the path straight.
Why it happens: It is exactly the same push as in Activity 1. The air rushes backwards out of the neck; the balloon is pushed forwards. In the first activity the balloon could go anywhere. Here the straw is threaded on the string, so the balloon can only go along the string. That is why it travels neatly from one end to the other. A real rocket works in the very same way — it pushes hot gas out of the back and is pushed forward.
If it does not run well: pull the string tighter, use a lighter balloon, make sure the tape is not stuck to the string, and keep the neck of the balloon pointing straight backwards along the string.
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