Coefficient of Restitution in Sports Equipment

Coefficient of Restitution

• Measures the elasticity of the collision between an object and a given surface, represented as a number between 0 and 1
• 1 = perfectly elastic collision, 0 = perfectly inelastic collision, and 0-1 = imperfectly elastic collision
• Influenced by temperature, equipment and surfaces, and velocity
• A high coefficient of restitution (COR) means a high bouncing ball, while a low COR means a low bouncing ball
• A COR of 1 means the object rebounds to the same height/velocity, while a COR of 0 means no rebound

Moment of Inertia (MOI)

• Resistance of a body to rotational movement, calculated as mass x radius2
• Less mass of a body decreases the resistance to rotational motion, while increasing the radius increases the moment of inertia
• Altering the radius leads to a change in MOI, such as a gymnast tucking their head in during a somersault to decrease MOI

Angular Velocity

• The rate of change in angular position of a body, influenced by the moment of inertia
• Increasing the radius of rotation slows rotational movement, increasing MOI, while decreasing the radius increases angular velocity
• Examples include a gymnast tucking their body during rotation to increase angular velocity, or untucking to slow it down

Modifications and Applications

• Modifications made to sporting equipment, such as shortening tennis racquets or golf clubs, reduce MOI and make it easier to use
• The moment of inertia of the human body can be altered in various sports, such as throwing, diving, dancing, and gymnastics
• Techniques used to reduce MOI include bending at the elbow, tucking, and piking, while increasing MOI involves layouts, and spreading arms or legs