Definition
Work is the measure of energy transfer that occurs when an object is moved over a distance by an external force applied in the direction of the displacement. Mathematically, it is defined as:
- How to read: “Work W is equal to force F times distance d.”
- Meaning / when to use: Use to calculate the energy transferred when a constant force moves an object. One Joule (J) of work is done when a force of 1 Newton is exerted over a distance of 1 meter.
Why It Matters
Work is the fundamental currency of mechanical systems and thermodynamics. It is the direct measure of how much energy must be spent to change a system’s state (e.g. lifting a rocket, driving a car, compressing a gas). Understanding work allows engineers to calculate fuel requirements, battery capacity, and the maximum capability of any engine or machine.
Core Concepts
- Force-Displacement Trade-off: Mechanical systems (like levers or pulleys) can multiply force, but they can never multiply work. If you multiply the output force by 10, the output distance must be divided by 10, because input work must equal output work (assuming no friction).
- How to read: “The input force times the input distance equals the output force times the output distance.”
- Meaning: Conservation of energy—you cannot get more work out of a machine than you put into it.
- Thermodynamic Work: Work done by a system (e.g., a piston expanding) is energy leaving the system, while work done on a system is energy entering it.
- Work-Energy Theorem: The net work done on an object is equal to its change in kinetic energy:
- How to read: “The net work W net is equal to the change in kinetic energy delta K.”
- Meaning: Accelerating an object requires doing work on it; that work is stored as motion (kinetic energy).