When a skydiver is falling towards Earth, they experience two primary forces acting on them: gravitational force (weight) pulling them downward and air resistance (drag) acting upward against the direction of their fall.
Before the parachute opens, as the skydiver accelerates downward, the force of air resistance gradually increases as their speed increases. Air resistance depends on factors like velocity, surface area, and drag coefficient—so initially, the skydiver accelerates until the air resistance force balances the gravitational force, leading to a terminal velocity where the net force is zero.
When the skydiver opens the parachute, there is a significant change in the dynamics of the situation:
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Increase in Surface Area: The parachute increases the submerged surface area that the air must move around significantly, which increases the drag force (air resistance).
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Immediate Effect: Upon deployment of the parachute, the skydiver experiences a very rapid increase in air resistance due to the large surface area of the parachute catching the air. This sudden increase in drag exceeds the gravitational force acting on the skydiver.
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Deceleration: As a result of the increased air resistance, the skydiver decelerates rapidly at first. The acceleration becomes negative as the upward force of air resistance briefly exceeds the downward force of gravity.
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New Terminal Velocity: As the skydiver continues to descend, the forces will once again reach a point of equilibrium. This new terminal velocity will be much lower than the previous terminal velocity (before the parachute was opened), due to the greatly increased drag force caused by the opened parachute.
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Stabilization: Eventually, the skydiver will stabilize at this new, lower terminal velocity, at which point the forces of gravity and air resistance will be balanced again.
In summary, the moment the parachute opens, the force of air resistance drastically increases due to the expanded surface area, causing the skydiver to decelerate until a new, lower terminal velocity is reached where the forces are again balanced.