Question

Describe the energy transformations that occur from the time a skydiver jumps out of a plane until landing on the ground.

Answer 1

Brief overview: most of the skydiver’s initial energy is gravitational potential energy (PE = mgh). As the fall proceeds that PE is converted into kinetic energy (KE) and—because of air resistance—into other forms (mainly thermal and sound). Below is a stage-by-stage description.

1. Just after jumping
- Initial energy: gravitational potential energy relative to the ground (mgh).
- Conversion begins: PE → KE as the skydiver accelerates downward.

2. Free fall with air resistance
- PE continues to convert to KE.
- Air resistance (drag) does work against the motion. That converts some of the mechanical energy into:
- Thermal energy (heating of the air and the suit/parachute fabric),
- Sound (air noise),
- A small amount of kinetic energy given to the air (air flow/wake).
- If drag grows enough, the skydiver reaches terminal velocity: weight = drag, so net force = 0 and KE becomes roughly constant while incoming PE is converted primarily into thermal and sound energy via drag.

3. Parachute deployment
- The parachute suddenly increases drag. Much of the skydiver’s KE is converted rapidly into:
- Work to inflate and accelerate a large mass of air (air gains kinetic energy briefly),
- Thermal energy (friction and viscous heating in the air and fabric),
- Elastic energy in the parachute lines and harness as they stretch,
- Sound (a snap/pop or whoosh).
- The net effect is a large loss of KE (deceleration).

4. Descent under canopy
- With the parachute open, the skydiver descends slowly. Remaining PE continues to convert slowly into energy dissipated by drag: mainly thermal in the air/fabric and sound. KE remains relatively small and nearly constant.

5. Landing
- The remaining KE (and any elastic energy stored) is removed by doing work on the ground and the body:
- Energy goes into deformation of the ground/harness/body, converted to thermal energy and sound,
- Muscles absorb some energy (controlled flexing), and some elastic energy may be returned (bounce) or dissipated.
- After coming to rest the initial PE has been accounted for as KE at intermediate times plus the various dissipated forms (thermal, sound, air kinetic, and some stored/released elastic energy).

Energy accounting (conceptual)
- mgh (initial PE) = KE (during fall) + energy dissipated by drag (thermal + sound + air kinetic) + energy absorbed/stored by parachute and body (elastic) + energy transferred to ground at landing.
- Conservation of energy holds; the useful mechanical energy is largely converted to heat and sound rather than vanishing.