Activity 3 — the wooden strip
The resultant of two parallel forces can be measured with a wooden strip and three Newton balances.
Activity 3
Apparatus: a wooden strip drilled with three holes as in the figure, three Newton balances.
- Make three holes x, y and z in a wooden strip and connect the three Newton balances A, B and C to those three holes.
- Pull with the Newton balances so that the wooden strip stays at rest.
- Always apply equal forces to the two balances A and B, and keep the Newton balances perpendicular to the wooden strip.
Figure to be added
Observation
With the wooden strip at rest, you will find that the readings of Newton balances A and B added together equal the reading of Newton balance C.
The reason is that the magnitude of the resultant of forces A and B equals the magnitude of force C.
Why keep A and B equal?
If A and B are unequal the wooden strip starts to turn — it is then no longer at rest, and the resultant cannot be read off C. Keeping the two forces equal, and the balances perpendicular to the strip, removes the turning and leaves only the sum.
Turning — the turning effect of parallel forces — is a topic of its own, and this chapter does not set out to teach it.