Question

Why must all forms of energy be changed into kinetic energy before work can be accomplished?

Other forms of energy cannot be used to accomplish work.
All work requires an object to move.

Answer 1

Short answer: No — other forms of energy can do work, but whenever work is actually done there must be a displacement, so some motion (and therefore kinetic energy at some scale) appears during the transfer.

Why: By definition work = ∫F·dx — there must be a force acting through a distance. That means some part of the system moves while the force is applied. In many processes the energy stored as chemical, electrical, thermal, or potential energy is converted (at least temporarily) into motion of something (macroscopic motion or microscopic motion of particles) that produces the displacement required for work.

Examples:
- A falling object: gravitational potential energy → kinetic energy → does work when it hits and deforms something.
- A battery powering a motor: chemical energy → electrical energy → moving charges (current) → motor shafts rotate (kinetic) → do mechanical work.
- Heat in a gas: thermal energy (random kinetic energy of molecules) creates pressure that moves a piston, doing work in a heat engine.

So it’s not that only kinetic energy can be “used” for work; rather, to accomplish work there must be movement, and that movement implies kinetic energy at some stage of the energy transfer.