계산 방법 마찰 힘 (Ff = μN): Static & 운동

계산 friction with Ff = μN. Static vs kinetic μ, normal 힘 on ramps, 일ed examples, and a free friction calculator.

What 마찰 Asks

마찰 is the 힘 that opposes sliding between two surfaces in contact. In intro physics it is modeled as proportional to how hard the surfaces press together — the normal 힘 N — not directly to 무게 unless N happens to equal mg.

The core 공식 is Ff = μN. μ (mu) is the coefficient of friction, a dimensionless number that depends on the materials. N is in newtons; Ff is in newtons.

If you have μ and N (or need to find one unknown), open the free friction calculator first, then return here for static vs kinetic and ramp traps.

Static vs 운동 마찰

  • Static (not yet sliding): Ff ≤ μs N. Maximum before motion: Ff,max = μs N.
  • 운동 (sliding): Ff = μk N while the object moves.
  • Usually μs ≥ μk — it takes more push to start motion than to keep sliding.

    • 마찰 points opposite the sliding direction or the tendency to slide.

    수직 항력 First

    Ff = μN requires the correct N.

  • Flat horizontal floor, no extra vertical 힘s: N = mg.
  • Incline at angle θ from horizontal: N = mg cosθ.

    • Find N with the normal 힘 calculator before you plug into Ff = μN.

    On a ramp, combine with inclined plane rules: a = g(sinθ − μk cosθ) sliding down, and μs ≥ tanθ to stay at rest.

    Rearrangements

  • Ff = μN — friction 힘.
  • μ = Ff / N — find coefficient from a lab measurement.
  • N = Ff / μ — find normal 힘 when μ and Ff are known.

    • 풀이 예제

    예제 1: 10 kg box, μk = 0.40 on a floor

    N = mg = 10 × 9.8 = 98 N. Ff = 0.40 × 98 = 39.2 N opposite motion.

    예제 2: find μ

    Measured Ff = 25 N with N = 100 N. μ = 25/100 = 0.25.

    예제 3: 5.0 kg on a 30° ramp, μk = 0.20

    N = mg cos(30°) = 49 × 0.866 ≈ 42.4 N. Ff = 0.20 × 42.4 ≈ 8.5 N up the ramp.

    흔한 실수

  • Using mg instead of N on an incline.
  • Using μs when the block is already sliding (use μk).
  • Forgetting friction direction — opposite motion or tendency to move.
  • Treating μ as having 단위 — only Ff and N are in newtons.

    • 확인 It on the 계산기

    마찰 calculator — Ff = μN.

    Normal 힘 calculator.

    Inclined plane calculator.

    힘 calculator.

    학습 Ff = μN and confirm every dynamics home일 number on the calculator.

    문서

    • 탄성 위치 에너지 공식 (U = ½kx²): 계산기 & 예제
    • 계산 방법 전기 전력 (P = VI, I²R, V²/R)
    • 계산 방법 파동 속도 (v = fλ): 주파수 × 파장
    • 계산 방법 무게 (W = mg): 질량 vs 힘
    • 계산 방법 밀도 (ρ = m/V): 질량 ÷ Volume
    • 계산 방법 가속도 (a = (v − u)/t)

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