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SESK: Stuff Everyone Should Know · sesk.info/eng-friction-not-contact-area

In the basic dry friction model, does a wider contact area increase the friction force?

No: friction depends on the normal force and the materials, not the contact area.

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  1. Yes, friction grows with contact area
  2. No, it depends on normal force and materials ✔
  3. Only for metals

Why: The model is friction = coefficient times normal force. Spread the same weight over a bigger area and the pressure drops by the same factor, so the total friction stays about the same.

Huh, didn't know that: Static friction adjusts from zero up to a maximum before slipping begins.

The dad joke
I lay down flat on the floor to get more friction. I just got more nap.
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References

Answer: No, it depends on normal force and materials. The model is friction = coefficient times normal force. Spread the same weight over a bigger area and the pressure drops by the same factor, so the total friction stays about the same.

  1. OpenStax University Physics Volume 1: 6.2 Friction openstax.org/books/university-physics-volume-1/pages/6-2-friction
    but not on the amount of area in contact
    Checked 2026-10-10.

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