A plate of area 0.5 m² moves at 2 m/s over a 2-mm oil film on a fixed surface. The force needed is 40 N. Find the oil's coefficient of viscosity. Step 1: Velocity gradient dv/dy = 2 m/s / 0.002 m = 1000 s⁻¹. Step 2: Shear stress = F/A = 40 / 0.5 = 80 Pa. Step 3: η = stress / gradient = 80 / 1000 = 0.08 Pa·s = 80 centipoise. Answer: η ≈ 0.08 Pa·s — about 80 times thicker than water, a typical light machine oil. Thicker oil would need a larger force for the same speed.