Parachutists and snowflakes do not fall with a constantly accelerating motion due to the effects of air resistance. As they fall through the air, they encounter resistance from the air molecules, which creates a drag force that opposes their motion. This drag force increases with speed, so as they accelerate, the drag force also increases, eventually reaching a point where it balances out the force of gravity, causing them to reach a terminal velocity.

In the case of a parachutist, the drag force is primarily due to the large surface area of the parachute, which increases the amount of air resistance they experience. As they fall, the parachute opens and creates a large, billowing canopy that captures the air and slows their descent. The shape and design of the parachute are specifically engineered to maximize drag and achieve a controlled descent.

For snowflakes, the drag force is determined by their size, shape, and density. Larger snowflakes have a greater surface area and experience more air resistance, while smaller snowflakes have less surface area and encounter less drag. Additionally, the intricate dendritic structure of snowflakes creates additional air pockets that further increase drag. As they fall, snowflakes reach a terminal velocity that depends on their individual properties and the air conditions.

In both cases, the combination of gravity pulling the parachutist or snowflake downward and the drag force opposing their motion results in a constant velocity, rather than a continuously accelerating motion. This steady descent allows parachutists to safely descend to the ground and snowflakes to gently float to the Earth's surface.