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1.3 Physics Is Useful

Physics plays a role in nearly everything you do. You will see how physics applies to your life by doing

the Investigations and reading how physics is used in everyday situations. There are many careers that

use the concepts learned through a study of physics. This section describes a few examples.


Engineering is the practice of using scientific knowledge to develop technology. Technology includes

all the inventions and techniques humans have developed, such as cars, microwave ovens, computers,

and even the horse-drawn plow. Engineering and technology are based on the fundamental laws of

physics. For example engineers apply the laws of forces (Chapters 5 and 6) and strength of materials

(Chapter 27) to design a bridge that can carry traffic safely across a river (Figure 1.12).

Cell phones are designed by electrical engineers using the physics of electricity (Chapters 19-24) and

light waves (Chapter 18). A cell phone uses microwaves to carry your voice from the phone to a relay

station (Figure 1.13). The relay station sends the information to a switch, where it is routed to the

closest switch to the person you are calling. Your voice then passes from that switch to another relay

station, then to the destination telephone. Other engineers design the mechanical parts of the cell phoneso it will work properly.

Automobiles are also developed by engineers using physics. For example, engines are designed by

mechanical engineers using concepts of force, motion, energy, and power (Chapters 10-12). The

engine’s fuel—gasoline, is developed by chemical engineers also applying concepts from physics

Including temperature, heat (Chapters 25-26) and how different chemicals react with each other

(Chapter 29).

Even the manufacture of a simple plastic toy requires understanding physics. A machine (called a

molding machine) takes hot, liquid plastic and squirts it into a mold that has the shape of the toy. When

the plastic cools, it hardens and the mold is opened so the toy can be removed. Physics is used all the

way from the design of the molding machine, the plastic, its melting and the filling of the mold, to the

machine that opens the mold and removes the finished toy.

Medicine and health professions

Physics is important to physicians, athletes, and other people in careers that focus on the human body.

The body obeys the laws of physics just like everything else in the universe. One area where physics

knowledge is necessary is the instrumentation used in sports and medicine, such as an x-ray machine. A

second area is the working of the body itself, such as the flow of blood or the action of muscles.

Medicine today depends intensively on technology that is based on the laws of physics. For example,

you expect to go to a hospital and get an x-ray if you think your finger is broken (Figure 1.14). An x-ray

can show what lies beneath the skin, which otherwise could not be seen. X-rays are produced by

machines based on the physics of the atom (Chapters 28 and 30) and the properties of light (Chapter

18). X-rays are a high-energy form of light, just like light from the sun. For another example,

ultrasound equipment can take moving pictures of a baby before it is born using the properties of waves

and sound (Chapters 14 and 15).

Physics also applies to the internal working of the body itself. For example, arteriosclerosis is a disease

of the arteries that makes them smaller inside. Smaller arteries restrict the flow of blood and increase

blood pressure, increasing the risk of heart disease. The relationship between the flow of a fluid

(blood), pressure, and the size of an artery is part of physics (Chapter 27). Most living animals need to

stay warm to live. The relationship between temperature, heat, and energy is also part of physics

(Chapter 25).

Athletes and coaches make very direct use of physics. Almost all forms of sports involve forces and

motion, both of which are described by physics (Chapters 5 and 6). An athlete’s body uses energy to

perform activities such as swimming, running, or jumping. For example, the energy required to jump

over a high bar is described by physics (Figure 1.15 and Chapter 10). A bicycle is the most efficient

machine ever invented to transform forces from the human body into energy of motion. Bicycles work

on the principles of torque and rotating motion—again, all part of physics (Chapters 9 and 11).

Many trainers and coaches use biomechanics to help athletes reach their maximum performance.

Biomechanics is the science of forces and their interaction with the human body and its muscles. For

example, slow-motion video may be used to analyze the technique of a high jumper. The timing of the

jump and the forces applied by each leg can be determined by analyzing the video using the principles

of physics. High-jumpers can often improve by changing their technique to make more effective use of

those forces.

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