How fast does a skydiver fall?

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Title:
How fast does a skydiver fall?
Topic:
Parachute
Question:

How fast does a skydiver fall before opening the parachute?

Seed Expert Claude Baudoin writes:
The maximum speed of a person falling from an airplane is limited by air resistance (drag). You may have seen that skydivers extend their arms and legs outward. This increases the air resistance, and results in the lowest possible free-fall speed. If they retract their arms and legs, they fall faster.

You will experience air resistance (drag) if you carefully put your hand out of a fast moving or train. The drag is greatest if you have your hand open at 90 degrees to the direction of movement i.e. maximum surface area.

Drag force is directly proportional to the surface area resisting the flow, the viscosity ("thickness") of the medium (air in this case) and proportional to the square of the velocity of falling.

Drag force also depends on the shape of the falling object. If it is streamlined, drag will be low. If the object has sharp edges, it will have higher drag. This is the physics of aerodynamics, including turbulent flow and laminar flow of air around objects. Vehicle shapes are tested in a wind tunnel to improve their aerodynamics, reduce drag and so improve performance factors such as speed and fuel efficiency.

As a skydivers’ speed increases, drag force due to air resistance increases, until it balances the downward force of gravity due to the person's weight. At that point, the acceleration stops, since the forces are in balance, and the skydiver will keep the same speed, called terminal velocity. For a free-falling skydiver this is about 200 km/h (125 mph).