Step 1: A Nitinol wire (A_f = 60 °C) is bent into a hook at room temperature (martensite, easily deformed). Heated above 60 °C in hot water, it straightens. If the wire is 0.50 m long and was bent to 6% strain, how much does it recover? Step 2: Recoverable strain for Nitinol ≈ 8% max; 6% is within range. Step 3: Recovery ΔL = 0.06 × 0.50 = 0.030 m = 3.0 cm of straightening. Step 4: If constrained from straightening, it exerts recovery stress ~500 MPa — for a 1 mm² wire that's 500 N (~50 kg force) — enough to act as a silent actuator. Step 5: Cooling back below M_s returns it to deformable martensite; the cycle repeats thousands of times. Result: ~3 cm shape recovery, or 500 N actuation force when blocked — a heat engine in a wire.