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NCERT Solutions for Class 5th The World Around Us Chapter 6 The root bridge challenge — Activity 3

Book page 105 Updated on2026-09-19

Q1.
Try a ‘Root bridge challenge’ in class. Can you connect two chairs using string or sticks in a way that will hold a small toy?
Answer

Yes — and the design that works is the one that copies the real root bridge: many strands, spread wide, tied to each other and to both ends. One string alone will sag and let the toy slide off.

What you need. Two chairs, a ball of string or several long shoelaces, some straight sticks or rulers, sticky tape, and a small light toy.

Step 1 — Set it up. Put the two chairs back to back, about half a metre apart. Everything must stretch between them; nothing may touch the floor.

Step 2 — Try the simple ways first, and see them fail.

What you tryWhat happensWhy
One single string, chair to chairIt sags and the toy slides down to the middle and falls offNothing holds the toy sideways
Two strings side by sideThe toy still slips down between themThere is no floor between the strings
One stick laid acrossIt holds a very light toy, but rolls or tipsThe ends are not tied down

Step 3 — Build the bridge that works.

  1. Tie four strings from one chair to the other. Space them out so they lie side by side, like the rails of a ladder.
  2. Pull each one tight and knot it firmly to the chair leg. A loose string means a sagging bridge.
  3. Now lay sticks across the four strings, one after another, close together. These are the steps of the ladder.
  4. Tie or tape each stick to the strings at both ends. Do not skip this — untied sticks roll.
  5. Take two more strings and weave them over and under, across the sticks, to lace the whole thing together.
  6. Add two short strings from the outer edges up to the chair backs, like handrails. They stop the bridge from twisting.
  7. Now place the toy in the middle.

What you will see. The single string could not hold the toy at all. The woven bridge holds it easily, and hardly dips. Add a second toy and it still holds. The load is now shared by six or eight strands instead of resting on one.

Bridge designHeld the toy?Why
One stringNoAll the weight on one strand; it sags into a V
Two strings, nothing acrossNoNo surface for the toy to rest on
Four strings + sticks across, untiedOnly justThe sticks shift and roll apart
Four strings + sticks tied + strings woven throughYes, firmlyEvery part holds every other part; the weight is shared all over
How the real bridge is made: In Meghalaya, the Khasi and Jaintia people find a rubber-fig tree growing on a stream bank. They guide its long thin air-roots across the water — traditionally along a hollow betel-nut trunk laid as a guide. The roots keep growing. When they reach the far bank they take hold in the soil. Then, year after year, people twist the new roots together and weave in more. Roots that touch and rub for long enough actually join into one. It takes fifteen to thirty years before the bridge can be walked on — and after that it goes on getting stronger, because it is alive. Some are more than a hundred years old, and one at Nongriat has two levels, one above the other.
The thought to take away: A bridge of cement is at its strongest on the day it is finished, and weakens from then on. A living root bridge is at its weakest on the day it is finished, and grows stronger every year after. That is why Chandan says, we just have to look after them now.
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