Force as rate of change of momentum (F = dp/dt)

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F = dp/dt

What each symbol means

SymbolWhat it stands for
FNet external force (N)
pLinear momentum = mv (kg·m/s)
tTime (s)

When to use this

Most general form of Newton's 2nd law. Reduces to F = ma when m is constant. Essential for variable mass systems (rockets, conveyor belts). For constant force: FΔt = Δp (impulse-momentum theorem).