F = ma Kesalahan: Net Gaya vs Berat
Newton’s second law uses gaya resultan — the vector sum of all gayas — not whichever gaya you notice first.
F_net = m a — Gaya resultan dalam newton; massa dalam kilogram; a dalam m/s²
Jebakan 1: Using berat alone when other gayas act
Salah: Block on a table being pulled: set F_net = mg.
Benar: Horizontal pull problems: F_net is along the surface (pull − gesekan). Berat and normal often cancel vertically.
Perbaikan: Sketch all gayas, then sum components along the percepatan direction.
Jebakan 2: Forgetting gesekan opposes the tendency to slide
Salah: F_net = F_pull when a rough surface clearly has kinetic gesekan.
Benar: While sliding, F_net = F_pull − μk N (same line, opposite directions).
Perbaikan: Static gesekan can prevent motion entirely — then a = 0 and F_net = 0.
Jebakan 3: Putting kilograms into F_net
Salah: m = 2 kg, a = 3 m/s² → writing F = 2 without satuan thinking “2 kg of gaya.”
Benar: F_net = m a = 2 × 3 = 6 N.
Perbaikan: Gaya answers must be dalam newton when m is dalam kg and a dalam m/s².
Jebakan 4: Confusing F = ma with W = mg
Salah: Any time you see massa, automatically writing F = mg even when the question asks for horizontal percepatan gaya.
Benar: W = mg is gravitasi gaya. F_net = ma is whatever gaya resultan menghasilkan the stated percepatan.
Perbaikan: Ask: “Is gravity the only gaya, or the gaya resultan I need?”
Jebakan 5: Using a single gaya’s magnitude when gayas cancel
Salah: Two equal opposite pulls of 10 N → claiming F_net = 10 N.
Benar: Equal opposite gayas → F_net = 0 → a = 0 (if that is the full story).
Perbaikan: Gaya resultan is a sum of vectors, not “the biggest arrow on the diagram.”
Kesimpulan
F = ma needs gaya resultan dalam newton and massa dalam kilogram — bukan berat alone, and not a single gaya when others cancel or oppose it.
FAQ
Berapakah gaya resultan?
The vector sum of all gayas on the benda. That sum equals m a.
Is berat always the gaya resultan?
Only dalam free fall with gravity as the only gaya (idealized). Tables, strings, and gesekan usually add other gayas.
Latihan W = mg · Gaya Kalkulator · Gesekan Kalkulator · Berat Kalkulator · Bidang miring Kalkulator
W = mg Rumus Latihan · Cara menghitung Gaya (F = ma) · Massaa vs Berat Ujian Jebakan · Cara menghitung Gesekan