Science and the Realm of Physics

Science is a systematic approach to understanding the natural world. It involves discovering patterns, formulating explanations, and expressing general truths in the form of scientific theories and laws. Physics, in particular, seeks to describe how matter and energy interact in space and time. It provides the foundation for understanding a wide range of phenomena—from microscopic events inside the human body to large-scale motions across the universe.

Physics aims to explain how the world works, whether it’s the movement of ions across cell membranes, the flow of blood in vessels, or the motion of machines. In fact, nearly every aspect of modern life—and of medical technology—can be described using the laws of physics.

One striking example is the smartphone like the one pictured in Figure 2.2..

Smartphones, like many other technologies, rely on fundamental physics concepts such as electricity, magnetism, wave propagation, and energy transfer. The circuits inside a smartphone channel electrical currents based on well-understood physical laws. GPS systems, which are standard in mobile phones, apply physics equations involving speed, distance, and time to calculate your location and how long it will take to get somewhere.

While this may seem unrelated to health care, similar physics principles underlie many medical devices. For example, a cardiac monitor processes electrical signals in the body in much the same way a phone processes electrical signals through its circuits. Haptic feedback in smartphones—using tiny mechanical actuators to produce vibration—is also used in wearable medical devices to alert patients or caregivers.

Whether it’s understanding how a defibrillator works, how light is used in pulse oximeters, or how forces affect joints during rehabilitation, physics offers the framework for both explanation and innovation in health care. This course will help you connect these principles to your future clinical practice and technological environment.

Applications of Physics in the Health and Life Sciences

You don’t have to be a physicist to benefit from physics. In fact, many people use physics concepts daily—often without even realizing it. For students preparing for careers in healthcare, a basic understanding of physics can help explain the technology and physical processes you’ll encounter in clinical settings, as well as improve your decision-making when evaluating treatment plans or using medical devices.

For example, physics explains how a microwave oven heats food, why metal objects should not be placed inside, and how electromagnetic fields might interfere with pacemakers. (See Figure 2.3 and Figure 2.4) It helps us understand how radiation interacts with tissues, enabling healthcare professionals to assess the benefits and risks of X-rays or CT scans. It also explains everyday observations: a black car heats up more than a white one because dark colors absorb more thermal radiation—a concept that’s just as relevant when thinking about heat loss in burn victims or temperature control in incubators.

Physics is foundational to many other scientific disciplines. Chemistry, which explores how atoms and molecules interact, is built on physical principles at the atomic level. Anatomy and physiology—though biological in nature—rely on physics to explain blood flow, muscle contraction, hearing, and vision. Many aspects of physical therapy, exercise science, and biomedical engineering are based on mechanical and electrical principles. Even the electrical signals that transmit information through the nervous system depend on an understanding of voltage, current, and resistance.

Physics also plays a direct role in medical technologies and diagnostics:

• On the microscopic scale, physics helps us understand how molecules move across cell membranes, how ion channels work, and how pressure affects cells and tissues.

• On the macroscopic scale, it describes how the human body generates heat and performs mechanical work—how your muscles lift weight, how your lungs exchange gases, and how your heart pumps blood.

Figure 2.5 and Figure 2.6 show how physics relates to biological systems, including cell membrane dynamics and blood flow through vessels.

In medical diagnostics, physics enables life-saving technologies like:

• X-rays, which rely on the interaction of ionizing radiation with tissue;

• MRI (Magnetic Resonance Imaging), which uses magnetic fields and radio waves to visualize soft tissues;

• Ultrasound, which uses high-frequency sound waves to create images and measure blood flow;

• ECG/EKG and EEG, which monitor electrical signals in the heart and brain.

Physics is also involved in therapy. For instance:

• Radiation therapy uses precisely calculated doses of ionizing radiation to target and destroy cancer cells.

• Laser surgery and phototherapy rely on optics and light-matter interactions.

Even sensory experiences can be explained with physics—how your ears detect sound from a stethoscope, how your eyes perceive color, or how laser communication devices transmit patient data wirelessly.

You don’t need to study all of these applications in detail. What’s most important is learning the core principles of physics and developing the analytical skills to apply them in meaningful ways. Physics trains you to think critically, solve problems logically, and understand the deeper mechanisms behind the tools and systems you’ll use in your healthcare career. It’s also the most “universal” science—meaning that learning physics now will help you better understand biology, chemistry, and the technologies you’ll encounter in your future clinical work.

Models, Theories, and Laws; The Role of Experimentation

In science, we seek to describe the universe as it truly is—not as we imagine it to be. The laws of nature are concise, evidence-based descriptions of how the world behaves. These laws are not invented by humans; rather, they are discovered through careful observation and experimentation. Whether we’re studying blood flow in the circulatory system or radiation used in cancer therapy, physics laws help us make sense of the natural processes that underlie health and disease.

The process of scientific discovery is a human endeavor—full of curiosity, creativity, testing, failure, and breakthroughs. It is this process that has led to many of the medical tools and life-saving treatments we have today (See Figure 2.7 and Figure 2.8).

Scientific progress begins with observation—noticing patterns in nature and asking questions about them. For example, a physician might notice that patients with certain symptoms tend to respond better to a specific treatment. Over time, researchers design experiments, collect data, and develop ideas to explain what’s happening. These explanations may take the form of models, theories, or laws.

• A model is a simplified representation of something we can’t directly observe. For instance, we can’t see the structure of atoms with our eyes, but we can use models (like the planetary model of the atom) to explain how electrons behave and how atoms emit light (See Figure 2.9.).

• A theory is a well-supported explanation for observed patterns in nature. It is tested and refined over time by many scientists. For example, the kinetic theory of gases helps explain how oxygen moves into the bloodstream or how anesthetic gases behave during surgery.

• A law is a concise statement describing a general pattern in nature, usually expressed mathematically. Newton’s second law, F = ma, is one such example—it helps describe how forces affect mass and acceleration, whether you’re lifting a limb during physical therapy or calculating the force applied by a surgical tool.

Theories and laws are both supported by evidence, but they serve different roles. A law summarizes what happens, while a theory explains why it happens. Both guide our understanding and help predict future outcomes.

Some statements that apply to narrower situations are called principles, like Pascal’s Principle, which is used in understanding intravenous fluid dynamics and how pressure is transmitted in a hydraulic system.

The Evolution of Natural Philosophy into Modern Physics

The study of nature has fascinated humanity for thousands of years. In ancient times, what we now call science—including biology, astronomy, medicine, mathematics, and physics—was all part of a broader field called natural philosophy. The word physics comes from the Greek physis, meaning “nature,” and early thinkers like Aristotle studied everything from motion and anatomy to ethics and the stars. (See Figure 2.10, Figure 2.11, and Figure 2.12.)

As knowledge expanded during the Renaissance and beyond, natural philosophy began splitting into specialized disciplines. Physics retained its role as the foundation—focused on understanding matter, energy, motion, and forces. These core ideas are essential not only for studying the universe but also for explaining how the human body works and how medical devices function.

From the Renaissance to the late 1800s, physics developed as what we now call classical physics. This includes Newton’s laws of motion, thermodynamics, wave behavior, and electromagnetism—all of which are vital for understanding health-related systems like blood circulation, ventilators, ultrasound, and ECGs. But at the dawn of the 20th century, scientists encountered phenomena that classical physics couldn’t explain—especially at very high speeds and on very small scales.

This gave rise to modern physics: a set of revolutionary ideas and mathematical models that describe the bizarre yet real behavior of matter and energy at extreme conditions.

Although modern physics grabs headlines with concepts like black holes and quantum tunneling, classical physics still dominates in the healthcare environment. Why? Because it accurately describes most everyday conditions:

• Objects moving at low speeds (like blood flow or limb motion),

• Weak gravitational fields (such as Earth’s),

• And systems large enough to be seen under a microscope (like organs and tissues).

• Classical physics explains:

  • How forces affect joints and bones in physical therapy,

  • How energy is transferred during exercise or metabolism,

  • How pressure differences move air in and out of the lungs,

  • And how electrical circuits operate in medical devices like pacemakers.

While classical physics provides the foundation, modern physics is essential for understanding today’s advanced medical technologies:

• Quantum mechanics is used in MRI scanners, PET imaging, and the understanding of molecular interactions—especially in pharmaceuticals and radiation biology.

• Relativity plays a role in technologies like GPS (which affects surgical navigation) and in calculating radiation doses from fast-moving particles in high-energy treatments.

Together, quantum mechanics and relativity form relativistic quantum mechanics, which describes very small particles moving at very high speeds—critical in particle physics and high-end cancer therapies.

But don’t worry: you don’t need advanced mathematics to understand these principles. This course uses algebra-based approaches that will allow you to explore many ideas in modern physics—including atomic models, radiation, and nuclear medicine—without needing calculus.

Why Start with Classical Physics?

Even though modern physics is incredibly powerful, we begin this course with classical physics for two reasons:

1. It accurately describes most real-world conditions in medicine and biology.

2. It gives you the foundation needed to understand more complex ideas later on.

By learning classical physics first, you’ll build strong skills in problem-solving, reasoning, and real-world application. This will serve you well—whether you’re assessing how mechanical forces affect a healing joint, setting up medical equipment, or evaluating the safety and effectiveness of diagnostic tools.