Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

10.1 What We Mean By Force 255

As engineering students, you will encounter different types of forces such as wind forces,

drag forces, viscous forces, surface tension forces, contact forces, and normal forces during your

course of studies. In the next sections, we will explain two forces (spring and friction) that every

engineer regardless of his or her area of specialization should know.

Spring Forces and Hooke’s Law

Most of you have seen springs that are used in cars, locomotives, clothespins, weighing scales,

and clips for potato chip bags. Springs are also used in medical equipment, electronics equipment

such as printers and copiers, and in many restoring mechanisms (a mechanism that returns a

component to its original position) covering a wide range of applications. There are different

types of springs, including extension (or compression) and torsional springs. Examples of dif-

ferent types of springs are shown in Figure 10.4.

Hooke’s law (named after Robert Hooke, an English scientist who proposed the law) states

that over the elastic range the deformation of a spring is directly proportional to the applied

force, according to

Fkx (10.3)

(e) Translate

Smooth

surface (ice)

Smooth

surface (ice)

(f) Rotate

F

F

(a) Elongate

(c) Bend (d) Twist

(b) Shorten

F F

F

F

F

■Figure 10.3 Simple examples to demonstrate the tendencies of a force.

Thin plate

acting as a

spring

Linear

spring

Torsional

spring

■Figure 10.4

Examples of different types of

springs.

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