Q.Given below are two statements, one of which is labelled as Assertion (A) and the other is labelled as Reason (R). Read both the statements carefully : Assertion (A) : When an object or body is moving at a constant velocity, with no changes in speed or direction, it is dynamic equilibrium. Reason (R) : A cyclist in motion or the body position maintained by a sprinter on the track while running are examples of dynamic equilibrium. In the context of the above two statements, which one of the following is correct ? (A) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

Dynamic Equilibrium

Stand perfectly still, and staying balanced is relatively easy — your base of support does not change, and neither does the position of your centre of gravity. Now try to stay balanced while running, cycling, or performing a gymnastics routine. That is a completely different challenge, and it is the subject of dynamic equilibrium in biomechanics.

Static vs. Dynamic Equilibrium

Static equilibrium is balance while at rest — a body is in static equilibrium when it is stationary and all the forces acting on it are balanced, such as someone standing still or holding a plank position.

Dynamic equilibrium, by contrast, is balance while in motion. The body is moving, its centre of gravity and base of support are both constantly changing, and yet the overall system stays under control rather than falling over. A person walking is a good example: at any single instant during a stride, the body may technically be off-balance (the centre of gravity briefly outside the base of support), but the next footfall re-establishes a new base of support before a fall actually happens. The balance is maintained through continuous movement, not despite it.

Examples in Sport

• A cyclist balances by constantly making tiny steering and weight-shift corrections; a bicycle at a complete standstill is actually far harder to balance than one in motion.
• A gymnast on a balance beam performing a routine has to maintain dynamic equilibrium throughout every step, jump, and turn, re-establishing balance with each new foot placement. …