5.5 Friction

Static Equilibrium and Forces

• Block of wood remains at rest despite applied force; net force is zero.

• Friction prevents motion; essential for understanding static equilibrium.

Static vs. Kinetic Friction

• Static friction prevents movement until a maximum force is reached (static friction max).

• When movement begins, kinetic friction takes over, requiring less force to maintain movement.

• Typical values: Static friction force at motion initiation is around $1 ext{ N}$; kinetic friction force recorded at $0.75 ext{ N}$ for constant speed.

Characteristics of Friction Forces

• Static Friction:

  • Varies up to a maximum value based on applied force and normal force.

  • Static friction force adjusts to keep net force zero.

• Kinetic Friction:

  • Constant magnitude and acts opposite to the direction of sliding.

  • Coefficient of kinetic friction is generally less than that of static friction.

Factors Affecting Friction

• Roughness of surfaces: Different materials have different coefficients of friction.

• Normal Force (N): The force pressing the two surfaces together affects friction magnitude.

• Surface Area: The area of contact does not significantly affect friction force.

Understanding Friction Coefficients

• Static Friction Max Formula: $Fs^{max} = c0s imes N$

• Kinetic Friction Formula: $Fk = c0k imes N$

• Higher coefficients indicate more resistance to sliding (greater stickiness).

Applications and Examples

• Friction is essential for daily activities (walking, driving).

• Experimental setups show the behavior of static and kinetic friction in applied force scenarios.

• Equation and graphs help in visual representation of the behavior of static and kinetic friction forces under varying conditions.