The work-energy theorem is a fundamental concept in classical mechanics that states: the net work done on an object is equal to the change in its kinetic energy. In other words, when a force moves an object, the energy used to do the work is directly converted into the object’s motion.
Mathematically, if a force causes an object to accelerate, the work done by that force increases (or decreases) the object’s kinetic energy, which depends on its mass and velocity. If positive work is done, the object speeds up; if negative work (like friction) is done, it slows down.
For example:
- Pushing a sled increases its speed—your force does positive work, raising its kinetic energy.
- Braking a car applies a force in the opposite direction of motion—negative work reduces its kinetic energy.
This theorem forms a direct bridge between force-based and energy-based approaches in physics. It’s widely used in solving problems involving motion, machines, collisions, and energy conservation.