Why Do Spiders Survive Falls That Humans Cannot?

Understanding the Physics of Falling

Momentum is calculated as mass multiplied by velocity. Spiders, due to their light mass, are inherently more aerodynamic and propelled by forces beyond simple gravity.

Physics plays a crucial role in explaining why humans and spiders behave differently during gravity-induced falls. The equation for atmospheric resistance is directly proportional to the mass of a falling body. When a human falls spread eagle, they encounter significant air resistance at a maximum velocity of around 120 mph near sea level. However, due to their mass, this resistance either increases or decreases as the square of their size. A spider, with its much lower mass, can be supported by air, even floating long distances on a breeze.

Spiders and Atmospheric Forces

Darwin once proposed that spiders used the Earth's electric field to stay aloft, an idea supported by modern scientific tests, particularly by Morley and Robert. Spiders rely on their electrified hairs and abdominal movements to overcome this electric field, enabling them to glide through the air. Darwin's theory leans on the idea that the Earth's surface emits a downward current that is countered by an upward current from the sky, allowing spiders to navigate through this electric field effectively.

The phenomenon described by Darwin, however, is scientifically intriguing, though further investigations and explanations are still needed. By using strong electric field receptions and hair-like structures on their bodies, spiders activate an electrified flying mechanism, quite similar to how they 'parachute' or 'fly' without typical wings. This unique adaptation makes them wonderful explorers and travelers without falling prey to the same physics that often spells danger for humans.

Terminal Velocity and Biological Scaling

The relationship between terminal velocity, gravitational force, and atmospheric resistance is governed by fundamental biological scaling laws. The volume of a body increases cubically with size, whereas the surface area only increases quadratically. This means that a very small animal like a spider, due to its lower mass and higher surface area to volume ratio, experiences far less gravitational force per unit volume compared to a larger entity like a human.

When a human falls, the energy required to dissipate upon impact is significantly higher due to their greater mass and velocity squared by mass. In contrast, a spider's smaller mass and larger surface area mean that the forces are distributed more evenly, resulting in a much lower terminal velocity. The strength and endurance of a spider's muscles and exoskeleton, being proportional to area, can handle these forces more effectively.

This principle of scaling in biology logically explains why large objects (like humans) face much greater challenges when falling, while small organisms (like spiders) can survive falls that would be fatal to us. Therefore, the next time you see a spider out in the open fields or trees, marvel at this marvel of spatial physics and the ingenuity of these tiny, resilient creatures.