Types of Equilibrium

Types of Equilibrium

With respect to the state of a body, equilibrium is divided into two categories: static equilibrium and dynamic equilibrium. Both appear constantly in sport, and the CBSE Class 12 Physical Education course expects students to tell them apart with sporting examples, and to recognise which one a given skill depends on.

1. Static Equilibrium

For a body to be in static equilibrium it must be neither moving nor rotating — all the forces and torques acting on it add up to zero. For an object that is completely motionless, three conditions must be met:

1. The sum of all the vertical forces acting on the body is zero.
2. The sum of all the horizontal forces acting on the body is zero.
3. The sum of all the torques (turning effects) is zero.

In short, static equilibrium is the balance of the body during rest or in a stationary position. Because the body is not moving, an athlete has time to actively adjust posture, widen the base, and lower the centre of gravity to satisfy these three conditions — which is exactly why static-equilibrium skills reward careful, deliberate positioning before the moment of action.

Sporting examples: a gymnast holding a steady handstand or scale position, a shooter standing motionless before firing, an archer at full draw, a weightlifter holding a barbell overhead in the final lockout position, and a wrestler holding an opponent pinned.

2. Dynamic Equilibrium

Dynamic equilibrium is the state in which all the applied and inertial forces acting on a moving body are in balance, so that the body keeps moving with an unchanging speed and direction — that is, with constant velocity. Unlike static equilibrium, the body is not at rest, so balance has to be found and continuously re-found while the athlete is already moving: the base of support, muscular adjustments and centre-of-gravity position all change moment to moment. Holding this balance while moving requires maximising stability through posture, foot placement and core control.

Put simply, dynamic equilibrium is the balance of the body during movement.

Sporting examples: the body position a sprinter maintains while running down the track, a cyclist holding a straight line while pedalling, a soccer player dribbling the ball between defenders, a skater gliding and turning on ice, a surfer balancing on a moving board, and a gymnast travelling along a balance beam.

Static vs dynamic equilibrium — the key difference