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Science ·Class 9 Science

Activity 7.5 Let us experiment to verify the law of levers using a beam balance with coins. Class 9

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RBSEGuide
· Jul 03, 2026 · Reviewed & updated Sep 17, 2026 · 2 min read

Activity 7.5 Let us experiment to verify the law of levers using a beam balance with coins. Class 9


Activity 7.5 Let us experiment

Aim: To verify the law of levers using a beam balance with coins.

  1. Take a long scale (50 cm or larger), a piece of string, two paper cups (to act as pans), adhesive tape or a piece of thread and identical coins (to act as weights).
  2. Tie the string tightly around the scale at its midpoint. This string will act as the fulcrum. Hang the scale from this string using a stand or hook, so that it can swing freely. This scale will now act as a beam (Fig.).
  3. Fix paper cups to both ends of the beam using thread. These cups act as the pans of a balance. Check whether the beam is levelled. If it is tilted, adjust the hanging points of the pans until both sides balance equally.
  4. Place 1 coin in the left pan (call it effort) and 1 identical coin in the right scale pan (call it load). Observe that the beam stays horizontal.
  5. Add one more coin to the right pan, so that it contains 2 coins. The beam tilts. Move the heavier pan closer to the centre of the beam to balance the beam. Measure its distance from the centre.
  6. Repeat step 5 with 4 coins and then 8 coins in the right pan. Each time, note its distance from the centre that balances the beam.
  7. Record all observations and measurements, and complete the Table by adding more rows.

Observation:

Table: Number of coins in the left pan and its distance from the fulcrum

Result:

Number of Coins in left pan, n1 (Effort)Distance of left pan from the fulcrum, L1 (cm)Number of Coins in right pan, n2 (Load)Distance of right pan from the fulcrum, L2 (cm)
1L11L1 (equal)
12L12L1


Calculation:

The beam balances when n1 × L1 = n2 × L2

or, effort × effort arm = load × load arm

Thus, Mechanical advantage = [latex]\frac{\text { Load }}{\text { Effort }}[/latex] = [latex]\frac{\text { effort arm }}{\text { load arm }}[/latex]

Conclusion:

Hence, by increasing the effort arm, the lever applies a larger force F2 to the load than the effort F1. The lever thus allows us to gain a mechanical advantage equal to the ratio of the distances, i.e., = L1.