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1.1: Introduction

In this exercise, force and pressure are examined through direct observation in a qualitative manner. Force may be computed by multiplying the mass of an object by acceleration:

$f=ma\nonumber$

If the mass is measured in kilograms and the acceleration in meters per second squared, the resulting unit of force is kilogram meters per second squared, or newtons (N). For comparison, one pound of force is equivalent to approximately 4.45 N. A mass sitting on the Earth is affected by Earth’s gravitational acceleration, 9.8 m/s2, so the force acting on it at rest (i.e., its weight) is the mass in kg times 9.8 m/s2.

Pressure is defined as force per unit area:

$p=f/area\nonumber$

Given a force in Newtons and an area in square meters, the resulting unit (Newtons per square meter) is called a Pascal (Pa). Note that pressure can be increased by either increasing the force or by decreasing the area. Even a modest force can produce extremely high pressure if it is applied over an exceedingly small area.