Question

The point on an extended massive object attached to a pivot where a perpendicular impact will produce no reactive shock at the pivot is known as:

• A. Centre of gravity
• B. Centre of mass
• C. Moment of inertia
• D. Centre of percussion

Hint:

Think of a baseball bat: the "sweet spot" where you feel no "sting" or vibration in your hands upon hitting the ball is exactly the Centre of Percussion.

Answer 1

The Correct Option is D

Concept: The Centre of Percussion (CoP) is a specific point on a rotating rigid body where a force can be applied without causing any reactive force (shock) at the axis of rotation (pivot).

Step 1: Understanding the physics.
When an object is struck, it tends to translate and rotate simultaneously.
• Translation tends to push the pivot in the direction of the blow.
• Rotation tends to pull the pivot in the opposite direction. When the blow is struck exactly at the Centre of Percussion, these two effects perfectly cancel each other out at the pivot point.

Step 2: Location of CoP.
If $L$ is the distance from the pivot to the CoP, and $k$ is the radius of gyration about the pivot, then: \[ L = \frac{k^2}{r_g} \] where $r_g$ is the distance from the pivot to the center of gravity.