It’s a hot muggy day on the steep slopes of a Malaysian rainforest. About 60 feet (20 m) above the jungle floor, a small brownish-red acrobat ant clambers out of a nest hidden under the whitish-gray bark of a macaranga tree. Locking clawed back feet into the tree trunk, she follows an ant-laid chemical trail down the trunk to forage for insects. A monkey hurtles past, brushing her off. Falling, the ant wildly splays her legs like a parachute to slow her descent, and spirals downward, picking up speed. In less than a second, she reaches terminal velocity, about 4 mph (6.4 km/hour), and falls at that speed until she hits ground. She crawls away — unhurt — to search for a chemical path back home, high above.
How do ants fall such vast distances and survive? Easy. Two factors save them:
– They have so little mass relative to their air resistance that they fall slowly and, therefore, have little energy to dissipate when they hit.
– Their bodies are tiny deformable tanks, well designed to absorb blows.
Falling slowly
Ants, like all objects falling through the atmosphere, have a terminal velocity that depends on their shape, size, and mass. An ant picks up speed as she falls through the air. The air, in turn, resists her movement with a force proportional to the square of her speed. Eventually she reaches a speed at which the upward drag forces exactly balance her downward weight and she stops accelerating. That speed is her terminal velocity.
The terminal velocity of a small to medium ant is about 4 mph (6.4 km/hour), according to the physics department of the University of Illinois. An ant would fall faster, given a ball-like shape, but the ant’s no dummy. She thrusts her legs out, presenting more surface to the air, to fall slower, like a flat sheet of paper instead of a balled-up sheet. Indeed, a man has a terminal velocity of about 125 mph (200 km/hour) with arms and legs fully extended to catch the wind like a parachute and about 200 mph (320 km/hour) when curled into a ball. An ant slows similarly.
But, it isn’t falling that hurts, it’s the sudden stop. Hitting ground, however, reaps the big benefits of falling slowly. When the ant hits, she must dissipate her falling (kinetic) energy in order to halt. That kinetic energy depends on the square of the velocity — not just velocity. So she must dissipate much less energy on impact, than say a man falling at a higher velocity. An ant goes 4 mph when she hits — about 1/30th times slower than a falling man on impact. She absorbs only 1/26,000,000th (1/26 millionth) times the energy of the man (assuming an ant weighs 1/10th of an ounce (0.3 g) and a man 180 pounds (82 kg)). No wonder the man probably dies and the ant walks away, unhurt.
“Sufficiently small animals cannot be hurt in a fall from any height: A monkey is too big, a squirrel is on the edge,
taken from happy news !!
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