Lesson 6 of 11 · 7 min
Equilibrium of a particle
NCERT § "Equilibrium of a Particle"
Over the stadium gate hangs a 10 kg team banner, held at one knot by two ropes: one at 30° above the horizontal, the other at 60°. Which rope is working harder?
The lesson in notes
In short
A particle is in equilibrium when the net external force on it is zero; it is then at rest or in uniform motion.
Two forces keep a particle in equilibrium only if they are equal in size and opposite in direction.
Three concurrent forces in equilibrium add to zero and can be drawn head to tail as a closed triangle.
In practice, resolve every force along two perpendicular axes and set the sum of components along each axis to zero.
A mass hanging from two strings is the standard case: the vertical components of the tensions together balance the weight, and the horizontal components cancel.