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Laws of friction; usage in engineering

Short answer

Laws: friction opposes motion, self-adjusting up to limit, F_max = μN, independent of area, depends on surfaces, kinetic μ_k < μ_s. Engineering uses: brakes and clutches use friction to stop or transmit torque; belt drives transmit power via friction (T1/T2 = e^(μθ)), and friction grip bolts carry load through friction between clamped plates.

Explain the laws of friction. Also give two examples of engineering usage of friction.

Laws of friction

  1. The friction force acts along the surfaces in contact and opposes the motion or the tendency to motion.
  2. For bodies at rest the friction force equals the applied tangential force, up to a maximum: F ≤ μₛN.
  3. The limiting friction is proportional to the normal reaction, F_max = μₛN.
  4. It does not depend on the area of contact.
  5. It depends on the nature of the surfaces (μₛ).
  6. Sliding (kinetic) friction is F = μₖN with μₖ < μₛ, and is almost independent of the speed of sliding.

Two examples of engineering usage

  1. Brakes and clutches: the braking force in vehicles (disc and drum brakes) and the torque transmitted by a clutch plate come from friction. Brake torque = μ N r.
  2. Belt drives and friction grip bolts: a belt transmits power to a pulley by friction (T₁/T₂ = e^(μθ)); friction-grip bolts in steel joints carry the load by friction between the clamped plates. Other uses: screw threads and nails holding by friction, walking and tyre grip on roads.

✓ Answer checked by Claude Opus 5.5 (high effort)

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