EXSS 385: Biomechanics of Sport - Friction

Vocabulary flashcards covering static and kinetic friction, normal forces, contact area independence, and real-world biomechanical applications from EXSS 385.

Friction Force

The force acting at the interface of surfaces in contact that acts parallel to the contact area and opposes motion or the tendency to move.

Normal Contact Force ($R_n$)

The force acting perpendicular to the contact surfaces that directly affects the total friction force.

Coefficient of Friction ($\mu$)

A dimensionless value indicating the relative ease of sliding between two surfaces in contact, influenced by surface roughness, hardness, and molecular interactions.

Maximum Static Friction ($F_m$)

The peak static friction force that must be exceeded to initiate motion, defined by the formula $F_{max} = \mu_s R_n$.

Kinetic Friction ($F_k$)

The constant friction force opposing motion between two surfaces sliding past each other, defined by the formula $F_k = \mu_k R_n$.

Static vs. Kinetic Friction Relationship

The mechanical rule where the static coefficient of friction is greater than the kinetic coefficient of friction ($\mu_s > \mu_k$), making kinetic friction force less than maximum static friction force ($F_k < F_m$).

Contact Area Independence

The principle stating that friction force does not depend on the surface area of contact, but only on the coefficient of friction ($\mu$) and the normal reaction force ($R_n$).

Pulling Effect on Friction

The mechanical outcome where pulling an object creates an upward vertical force component ($P_v$), reducing the normal force ($R = \text{wt} - P_v$) and lowering friction.

Pushing Effect on Friction

The mechanical outcome where pushing an object creates a downward vertical force component ($P_v$), increasing the normal force ($R = \text{wt} + P_v$) and increasing friction.

High Friction Applications in Sports

Equipment designed to maximize traction and prevent slipping, including rubber athletic shoe soles, leather or rubber grips, chalk, tape, and tacky sprays.

Low Friction Applications in Sports

Equipment designed to facilitate sliding or gliding, including smooth soles for dancing and bowling, and ski wax for snow skiing.