Physics
Terminal Velocity
Quick fact
A skydiver in a belly-to-earth position reaches a terminal velocity of about 120 mph (193 km/h), while a skydiver in a head-down dive can exceed 200 mph (322 km/h).
Why this is interesting
Ever wonder why a skydiver doesn't keep speeding up until they hit the ground? What stops them from accelerating forever?
Read the full explanation
Understanding Terminal Velocity
Imagine dropping a feather and a rock from the same height. The rock plummets, the feather flutters. That difference is because air resistance affects them differently. Terminal velocity is the speed where air resistance (pushing upward) exactly balances gravity (pulling downward). Before reaching that speed, gravity is stronger and the object accelerates. As speed increases, air resistance grows until it matches weight. After that, no net force remains → no acceleration → constant speed. This is why a skydiver feels a stable fall once they've fallen far enough.
A deeper explanation
Terminal velocity arises from Newton's second law (F=ma) applied to an object in a fluid. Two main forces act: weight (mass × gravity, constant) and drag (approximately proportional to the square of velocity for most objects). As velocity increases, drag rises. When drag equals weight, net force is zero, so acceleration stops. The object then falls at constant speed—its terminal velocity. This speed depends on the object's mass, cross-sectional area, shape, and the fluid's density. A streamlined shape reduces drag, leading to a higher terminal velocity. Understanding terminal velocity is crucial for designing parachutes (which increase drag to lower terminal speed), analysing meteor impacts, and explaining why hailstones have a maximum size—they fall at terminal velocity and grow until air can no longer support them.