ABSTRACT
Gravity, Weight, and the Lifting Force Gravitational attraction acts on the mass of all matter, pulling any two objects together. Normally, we perceive only the pull of one close-by massive object, the earth, but in fact all objects attract all others gravitationally (trivia: two 10 lb objects 1 foot apart exert a gravitational attraction force of about 1 billionth of a pound on each other). By convention, the force developed due to the gravitational pull of the Earth is called weight, and many texts therefore give it the symbol w. In this book, a force is a force regardless of its origin, and so for consistency weight will be expressed as . Every person has learned through experience to gauge how hard it might be to move something by hand. An object’s apparent weight and the direction it needs to be moved affects this assessment. Lowering is easier than lifting, rolling something up a ramp can seem more practical than lifting that thing straight up the same vertical distance, and moving anything across a level floor is simple once friction is reduced. While this intuition is useful, it provides no precise values that would allow, for instance, a motor horsepower to be picked with confidence. A formulaic approach is needed.
