Physics · Class 11

Balance three forces

Equilibrium requires the net force to vanish in every direction. Three large pulls can balance because their vector components cancel. Changing a magnitude or direction usually leaves a resultant. The required third force is the negative of the sum of the first two.

Open the interactive experiment →

A balanced knot has no leftover arrow.

சமநிலையில் ஒவ்வொரு திசையிலும் நிகர விசை பூஜ்யம். மூன்றாவது சமநிலை விசை முதல் இரண்டு விசைகளின் கூட்டுத்தொகைக்கு எதிர்திசையில் இருக்கும்.

Key notes, relationships and model limits

Key relationship

ΣFx = ΣF cosθ = 0; ΣFy = ΣF sinθ = 0; Fbalancing = −(FA + FB).

Remember

Common trap

Adding force magnitudes alone cannot test equilibrium; directions matter.

Model limits

Three concurrent forces act on an ideal knot. The display tests translational equilibrium only; no moments or string elasticity are modeled.

What you will learn

Resolve concurrent forces and find the balancing force.

Try the experiment

Begin at the balanced knot. Change one direction, then use the required-C readout to restore balance.

Think of it this way

Three people can hold a ring steady by pulling ropes in carefully matched directions.

Worked example

Two 10 N pulls at 30° and 150° have cancelling horizontal components and total upward component 10 N. A 10 N downward pull balances them.

Why this matters

Component equations turn a visual balancing problem into two manageable scalar equations.

Before you start

Vector components · velocity · SI units

Check your understanding

For translational equilibrium in a plane, which condition is required?

Only ΣFx = 0
Both ΣFx = 0 and ΣFy = 0
All individual forces must be zero

Read the explanation

Both independent components of the resultant must vanish.

Course connection: CBSE XI Chapter 4; NEET/Main Unit 3; JEE Advanced Mechanics. Apply each exam’s stated assumptions.