Two Skydivers, Two Top Speeds

In the picture

1. 1Thin red arrow: the solo skydiver’s weight pulling down.
2. 2Thin yellow arrow: air drag pushing up, now as strong as the weight, so the speed stays steady.
3. 3Thick red arrow: the pair’s weight, about twice as big, on the same frontal area.
4. 4Thick yellow arrow: drag only matches that bigger weight once the pair is falling much faster.
5. 5Long wind streaks: the pair’s steady speed is higher than the solo skydiver’s.

Examples

• Two paper cupcake cases stacked together fall faster than one alone, because they have the same shape but twice the weight.
• A badminton shuttlecock with a coin taped inside falls faster than a plain one of the same shape.

Quiz: Two Skydivers, Two Top Speeds (Age 14)

1. 1

   Why does a falling skydiver eventually stop speeding up?

   • Gravity gets weaker the longer they fall.
   • The air’s upward push grows until it equals their weight.
   • Their weight stops pulling on them once they reach top speed.
2. 2

   Two skydivers have the same body size and position, but one is twice as heavy. Which one reaches the higher steady falling speed?

   • Neither: they settle at the same speed, because gravity speeds everything up equally.
   • The lighter one, because it cuts through the air more easily.
   • The heavier one, because the air must push harder to balance its weight.
3. 3

   A tandem pair and a solo skydiver are each falling at their own steady speed. How does the air drag on the pair compare with the drag on the solo skydiver?

   • About twice as big, because it matches the pair’s bigger weight.
   • The same, because they meet the air with the same body area.
   • About half as big, because the drag is shared between two people.

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.