Falling into water from significant heights often sparks curiosity about survival. While water appears soft, it can transform into an unyielding surface upon high-speed impact. The gentleness of water belies its danger when a body strikes it at speed. Understanding the forces involved can illuminate why a seemingly safe landing can lead to severe injury or fatality.
Understanding the Descent
The physics of a fall begins with gravity, a constant downward force. As a person falls, gravity accelerates them, increasing their speed. Simultaneously, air resistance, or drag, opposes this motion, pushing upwards.
As speed increases, so does air resistance. Eventually, the upward force of air resistance equals the downward force of gravity. At this point, the body stops accelerating, reaching a constant speed known as terminal velocity. For a human, terminal velocity ranges from 120 to 200 miles per hour, depending on body position and mass.
The Force of Water Impact
When a body traveling at high speed strikes water, it behaves less like a fluid and more like a solid. This occurs because water molecules cannot be displaced quickly enough by the rapidly approaching body. Water is nearly incompressible, resisting being squeezed.
The rapid deceleration generates immense pressure and force on the impacting body. This sudden stop can impart forces similar to striking a hard surface. The force of impact depends on the speed of the fall and the surface area that hits the water.
Effects on the Human Body
The sudden, powerful impact with water from a significant height can cause severe physiological damage. Injuries often include broken bones, especially spinal compression fractures. Internal organs are also highly susceptible to trauma. Organs like the lungs can suffer contusions, and others may rupture due to immense pressure and rapid deceleration.
Spinal injuries and concussions are possible, depending on body orientation. The severity of injury is significantly influenced by body position at the moment of impact; a flat-body impact (e.g., a “belly flop”) distributes force over a larger area, leading to widespread damage. A feet-first entry concentrates force through the lower extremities and spine. Even with a feet-first entry, injuries like shattered ankles, harm to knees, legs, hips, and pelvis, and severe bruising to internal organs are common at higher velocities.
Strategies for Safety
If a fall into water from a height is unavoidable, specific body positioning can minimize injury. The recommended technique is to maintain a straight, vertical, feet-first entry. This streamlined entry reduces the surface area hitting the water first, allowing for more gradual deceleration.
Keeping limbs close to the body, with arms held tightly at the sides or crossed over the chest, can prevent flailing and reduce the risk of dislocated joints or broken bones upon impact. Exhaling before impact can reduce lung damage or rupture due to hydrostatic shock. Water depth is also a factor; shallow water presents the danger of hitting the bottom, which is as damaging as hitting a solid surface.