Q1.
Record all observations and measurements, and complete the Table 7.1 by adding more rows. [Number of coins in the 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)]
Answer
Keep the left pan (1 coin) at a fixed distance — say L1 = 20 cm — and slide the loaded right pan until the beam is level each time. A typical completed table:
| Coins in left pan, n₁ (effort) | Distance L₁ (cm) | Coins in right pan, n₂ (load) | Distance L₂ (cm) | n₁ × L₁ | n₂ × L₂ |
|---|---|---|---|---|---|
| 1 | 20 | 1 | 20 | 20 | 20 |
| 1 | 20 | 2 | 10 | 20 | 20 |
| 1 | 20 | 4 | 5 | 20 | 20 |
| 1 | 20 | 8 | 2.5 | 20 | 20 |
The last two columns are always equal, so the beam balances when
n1 × L1 = n2 × L2
that is, effort × effort arm = load × load arm (Eq. 7.15)
Mechanical advantage = load / effort = n2/n1 = L1/L2
Row 4: MA = 8/1 = 20 cm / 2.5 cm = 8
n1 × L1 = n2 × L2
that is, effort × effort arm = load × load arm (Eq. 7.15)
Mechanical advantage = load / effort = n2/n1 = L1/L2
Row 4: MA = 8/1 = 20 cm / 2.5 cm = 8
Why it happens: the beam is a class-I lever with the string as fulcrum. Each coin is an identical weight, so the number of coins measures the force directly. Doubling the load must halve its distance from the fulcrum, because it is the product force × arm that has to match on the two sides.
Tip: use identical one-rupee coins and a stiff plastic scale, and hang the pans with thin thread so the arm length is easy to read. If the empty beam is not level to start with, shift one pan slightly until it is — otherwise every reading is thrown off.