Physics · Ch 6 — Work, Energy and Power
Introduction
Introduction
The Everyday Words, the Physics Meanings
The words work, energy, and power are part of our daily vocabulary. A farmer ploughing a field, a construction worker carrying bricks, a student studying for an exam — all are said to be "working." In physics, however, the word work has a very specific and precise meaning. It is not a synonym for effort or activity.
Similarly, we say someone who can work for 14–16 hours a day has great stamina or energy. We admire a long-distance runner for her energy. In physics, energy is indeed related to work — it is the capacity to do work. But because the term work itself is defined so precisely in physics, the definition of energy inherits that precision.
The word power is used in everyday life with different shades of meaning. In karate or boxing, we talk of "powerful" punches — delivered at great speed. This shade of meaning is close to the physical definition of power, which involves the rate at which work is done.
There is at best a loose correlation between the physical definitions of work, energy, and power and the physiological pictures these terms generate in our minds. Do not rely on everyday intuition when solving physics problems.
The aim of this chapter is to develop a rigorous understanding of these three physical quantities. Before we can proceed, we need a mathematical prerequisite: the scalar product (also called the dot product) of two vectors.