--- kf_03-19T15-06-15-227478.py
+++ kf_03-19T15-50-07-090361.py
@@ -495,6 +495,14 @@
                       math.cos(hour_angle_rad))
     sin_elevation = max(-1.0, min(1.0, sin_elevation))
     return math.degrees(math.asin(sin_elevation))
+def vertical_shadow_length(height: Distance, solar_elevation_deg: float) -> Distance:
+    if not isinstance(height, Distance):
+        raise TypeError("height must be a Distance instance.")
+    if solar_elevation_deg <= 0:
+        raise ValueError("solar_elevation_deg must be positive.")
+    height_m = height.value.convert_to(meter_unit).number
+    shadow_m = height_m / math.tan(math.radians(float(solar_elevation_deg)))
+    return Distance(Value(shadow_m, meter_unit))
 hockey_puck = PhysicalObject(
     name=Name('hockey_puck'),
     mass=Mass(Value(0.170, kilogram_unit)),
@@ -507,3 +515,11 @@
     name=Name("hot_wheels_car"),
     mass=Mass(Value(0.035, kilogram_unit)),
 )
+bic_crystal_pen = PhysicalObject(
+    name=Name('bic_crystal_pen'),
+    mass=Mass(Value(0.050, kilogram_unit)),
+    shape=Cylinder(
+        radius=Radius(Value(0.45, centimeter_unit)),
+        height=Distance(Value(14.9, centimeter_unit)),
+    ),
+)