Push a stalled car ten meters and you have done work. Hold a heavy box in place and you have done none, no matter how much your arms ache. In physics, work has a strict meaning: a force moves an object, and energy transfers in the process. Effort alone does not count.

The formula is force times distance, measured in joules. Lift a 5-kilogram bag one meter, and you have done about 49 joules of work. Slide it across a table against friction, and the work goes into heat. The direction matters too. A force perpendicular to motion, like carrying a tray while walking, does no work on the tray at all.

Work connects force, energy, and motion. It is how energy moves between objects. An engine does work on a car to speed it up. Gravity does work on a falling rock. Friction does negative work, removing kinetic energy and warming the surfaces. Every machine is a device for doing work, and every inefficiency is work lost to unwanted heat.

Key points

• Work equals force times distance
• Measured in joules
• Force must move the object
• Direction of force matters
• Connects to the work-energy theorem