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Lesson: Chapter 12 — Equilibrium of Forces

12.2. Equilibrium under two forces 3 of 6

Activity 2 — the wooden block

Does a cubical wooden block give the same result as a ring? The second activity checks.

Activity 2

You will need: a cubical wooden block, two Newton balances, two rings for attaching the balances to the block.

  1. Attach the two rings to the centre points of the block's two opposite faces.
  2. Connect the two Newton balances to the rings and pull the block both ways, applying forces of various magnitudes.

Figure to be added

Figure 12.5 — pulling a wooden block both ways: two Newton balances connected to rings fixed at the centres of the block's opposite faces.

Observation

Whenever a resultant force exists, the block moves in some direction.

When equal forces are applied either way the resultant becomes zero and the block stays still.

So here too, in every case where the block is in equilibrium the two oppositely acting forces are equal in magnitude. What the ring gave, the block gives as well.

Why the centres of the faces?

The rings go at the centres of the faces so that the two forces act along one and the same line. Fixed at a corner, the two forces would not be collinear and the block would begin to turn — which is the turning effect met in chapter 11.