50 Technology: Engineering Our World Copyright Goodheart-Willcox Co., Inc. A product may be unsafe for three reasons. First, the design of the product may be defective. A stepladder may collapse because it has poorly designed hinges connecting its two sections. Second, there may be a defect in the product because of the way in which it was manufactured. Perhaps the wrong material was used or a part is not strong enough. Third, the instructions that accompany the product may be unclear or incomplete, leading to inappropriate use or misunderstanding. Some products are designed specifi cally to make peoples’ lives safer. A fi re extinguisher can prevent property damage and possible loss of life, if it is easy to understand and to use. A bicycle helmet can prevent serious head injury in the event of an accident. Finally, functional products do not need to be boring. They can also entertain. The key ring in Figure 3-12A functions perfectly. The jump-roping key ring in Figure 3-12B, however, brings a smile to the user’s face and, therefore, can be more fun to use. User-Centered User-centered design places the user at the center of designing. Products will be designed so their use is intuitive, that is, easy to understand and learn. For example, doors and their handles come in all shapes and sizes. In public places, emergency exit doors are required by law to have crash bars installed. Crash bars allow people who are running from an emergency to open the door without reducing their speed. Look at the crash bar in Figure 3-13A. On which side do you push it to open the door? This is an example of poor user-centered design. The crash bar in Figure 3-13B is an example of good user-centered design because a quick glance tells you on which side to push. B A ©TROIKA 2017 Germany GmbH Figure 3-12. Identify products in your home that could be redesigned to function well and entertain. AlexLMX/Shutterstock.com nicepix/Shutterstock.com Figure 3-13. Two types of crash bars. A—Which side of the crash bar do you push to exit in an emergency? B—The shape of this crash bar immediately tells you which side to push. A B Florin Burlan/Shutterstock.com