Key relationship
R=√(A²+B²+2AB cosθ); Fequilibrant=−R⃗.
Physics · Practical apparatus
Parallelogram force apparatus
Two measured string tensions add as vectors. A third string placed opposite the resultant balances the knot when its tension matches the resultant magnitude.
Open the interactive experiment →Parallelogram force apparatus
இரு விசைகள் திசையன்களாகக் கூடும். எதிர் திசையிலான மூன்றாவது விசை முடிச்சை சமநிலைப்படுத்தும்.
Key notes, relationships and model limits
Practical tip
Two measured string tensions add as vectors. A third string placed opposite the resultant balances the knot when its tension matches the resultant magnitude.
Common trap
The equilibrant points opposite to the resultant. It has the same magnitude, not the same direction.
Model limits
frictionless pulleys and massless strings; the third-force residual assumes its direction is opposite the calculated resultant.
What you will learn
Adjust parallelogram force apparatus apparatus, observe its reading and derive the indicated physical quantity.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
At 90°, R=√(3²+4²)=5 N, so a 5 N equilibrant at the opposite direction balances the knot.
Why this matters
The model connects parallelogram force apparatus with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
3 N and 4 N perpendicular tensions have resultant?
- 7 N.
- 5 N.
- 1 N.
Read the explanation
5 N.
Course connection: Virtual apparatus preparation. Check exact board/exam membership in the syllabus sources. Physical practical work remains necessary.