Physics

OpenStax Physics develops an algebra-based understanding of motion, forces, energy, waves, electricity, and modern physics across twenty-three chapters. Paul Peter Urone, Roger Hinrichs, and contributing authors connect physical models with experiments, representations, and everyday applications. The book asks readers to move between words, diagrams, graphs, equations, and units. This guide follows its chapter order, including relativity, quantum ideas, atomic structure, and particle physics, and emphasizes choosing a suitable model before beginning a calculation.

Chapter-wise summaries and reading tasks

Chapter 1 What is Physics?

Physics studies patterns in the natural world by developing models that can be tested against observation. This opening chapter connects scientific questions, hypotheses, experiments, and revisions with the practical language of measurement. Physical quantities require units, and conversions preserve the quantity while changing its numerical representation. Precision, significant figures, and uncertainty help communicate what a measurement can support. A model is valuable because of the situations it explains and predicts, not because it describes every feature of reality. Learning to state assumptions and distinguish evidence from an interpretation establishes the reasoning used throughout the book.

Study task. Describe a testable physical question, identify measurable variables, and convert one relevant quantity between units while retaining an appropriate level of precision.

Chapter 2 Motion in One Dimension

One-dimensional motion is described relative to a chosen origin and direction. Distance records how much ground an object covers, whereas displacement compares its final and initial positions. Similarly, average speed and average velocity answer different questions, especially when an object reverses direction. Position–time graphs show location over time, while velocity–time graphs describe how motion changes. Graph slopes and areas connect those pictures with numerical quantities. Explicitly selecting a reference frame prevents a negative velocity from being mistaken for an impossible result. The same journey can have a large distance and zero displacement, illustrating why definitions must be settled before calculation.

Study task. Describe a trip out and back using distance, displacement, average speed, and average velocity. Sketch compatible position–time and velocity–time graphs with labelled axes.

Chapter 3 Acceleration

Acceleration describes a change in velocity per unit time, including a change that reduces speed. Its sign depends on the chosen direction, so negative acceleration does not always mean slowing down. The chapter connects equations for uniformly accelerated motion with the shapes of position and velocity graphs. A constant-acceleration model has a defined scope: it should not be applied to a situation merely because a problem contains time and velocity. Identifying known quantities, the desired quantity, and the assumed constancy of acceleration makes equation selection more systematic. Free-fall examples also separate gravitational acceleration from the direction in which an object happens to be moving.

Study task. Compare an object moving upward while slowing with one moving downward while speeding. State the velocity and acceleration signs under a single coordinate convention.

Chapter 4 Forces and Newton’s Laws of Motion

Newton’s laws connect a body’s motion with the net external force acting on it. The first law establishes inertia, the second relates acceleration to net force and mass, and the third identifies forces exerted by interacting bodies on each other. A free-body diagram includes forces acting on one selected object; it should not combine both members of an action–reaction pair on that same body. Balanced forces can accompany rest or constant velocity, while an unbalanced resultant changes velocity. Distinguishing mass from weight and identifying the system boundary are essential before using the laws to calculate an unknown force or acceleration.

Study task. Draw a free-body diagram for a book on a table and identify the reaction partner of each force. Explain why the book’s weight and normal force are not a third-law pair.

Chapter 5 Motion in Two Dimensions

Two-dimensional motion is handled by combining vectors and resolving them into components. Graphical and analytical approaches represent the same quantities, but component calculations make complex directions easier to manage. Projectile motion combines horizontal and vertical behaviour under a stated idealization; inclined-plane problems benefit from axes chosen along and perpendicular to the surface. The chapter also introduces simple harmonic motion, where the restoring tendency depends on displacement from equilibrium. Across these applications, a vector’s direction matters as much as its magnitude. Component equations should be linked back to the physical diagram rather than treated as independent formulas without a shared coordinate system.

Study task. Resolve a vector into perpendicular components, then sketch a projectile trajectory. Explain which component changes under the ideal no-air-resistance model and why.

Chapter 6 Circular and Rotational Motion

Circular motion requires acceleration even when speed stays constant because velocity changes direction. The inward resultant is described as centripetal; it must be supplied by actual forces such as tension, gravity, or friction rather than added as an extra force. Angular quantities provide another language for describing rotation and link with linear speed through distance from the axis. Rotational motion extends the discussion to torque and the influence of how mass is distributed. Choosing a consistent rotational axis and recognizing which quantities are angular prevents confusion between a body’s turning rate and the speed of one point on it.

Study task. Identify the physical force supplying inward acceleration in two different circular-motion examples. Compare the linear speeds of two points at different radii on the same rotating object.

Chapter 7 Newton's Law of Gravitation

Gravitation links falling objects on Earth with orbital motion through one interaction. Kepler’s laws summarize patterns in planetary paths and periods, while Newton’s universal law relates attraction to masses and their separation. An orbit can be understood as continuous falling with sufficient sideways motion, rather than as a place where gravity disappears. The chapter also introduces general relativity as a different account of gravitation involving spacetime, placing Newton’s useful approximation within a wider theory. Readers should distinguish a descriptive orbital pattern from the explanatory model used to account for it and note the conditions under which each approach is appropriate.

Study task. Explain why astronauts in orbit can feel weightless while still experiencing gravity. Use a sketch to connect sideways motion with continuous inward acceleration.

Chapter 8 Momentum

Momentum combines mass and velocity and is particularly useful for studying interactions over short times. Impulse measures the effect of force acting through a time interval and equals the resulting momentum change. Conservation applies to a system when the relevant external impulse is negligible. In collisions, total momentum can be conserved even when kinetic energy is not, so elastic and inelastic events must be distinguished. The choice of system determines which forces count as internal. Signed velocities and a clear before-and-after diagram help prevent apparently conflicting answers when objects move in opposite directions.

Study task. Compare two ways to stop the same moving object over different times. Explain the force implication using impulse, then identify a system suitable for analysing a collision.

Chapter 9 Work, Energy, and Simple Machines

Work transfers energy through the component of a force along displacement, while power describes the rate of energy transfer. The work–energy theorem relates net work to a change in kinetic energy, and potential-energy models make it possible to track energy stored through position or configuration. A conservation approach requires accounting for energy transferred out of the selected system, including thermal effects associated with friction. Simple machines change the relationship between applied force and motion but do not create energy. The chapter therefore links calculation with a careful inventory of energy forms and transfers, making many motion problems easier to reason about.

Study task. Draw an energy account for an object sliding down a rough slope. Explain how a machine can reduce the required input force while increasing the distance through which that force acts.

Chapter 10 Special Relativity

Special relativity examines measurements made by observers in uniform relative motion. Its postulates place the laws of physics on an equal footing in inertial frames and assign a common vacuum light speed to those observers. Time dilation, length contraction, and the relativity of simultaneity follow from these ideas rather than from defective clocks or instruments. The chapter also connects mass and energy. A useful reading strategy is to identify which observer measures each quantity and which events are being compared. Everyday Newtonian predictions remain effective at sufficiently low speeds, but they cannot simply be extended unchanged to motion approaching light speed.

Study task. Describe an event pair and specify the observers who compare it. Explain why stating whose clock or length is measured is necessary before interpreting a relativistic effect.

Chapter 11 Thermal Energy, Heat, and Work

Thermal energy, temperature, and heat are related but distinct concepts. Temperature characterizes thermal conditions, while heat is energy transferred because of a temperature difference. Specific heat links an energy transfer to a temperature change for a given substance and mass. During phase changes, energy can alter the material’s state without producing the same kind of temperature increase. Conduction, convection, and radiation provide different mechanisms for thermal transfer. Keeping the system and surroundings explicit makes it possible to interpret cooling, warming, and changes of state without assuming that a material contains a substance called heat.

Study task. Compare heating water within one phase with melting ice at its transition temperature. Explain where the transferred energy goes in each case and identify the relevant material property.

Chapter 12 Thermodynamics

Thermodynamics studies how energy transfers and physical constraints govern macroscopic systems. Thermal equilibrium provides the basis for temperature comparison, while the first law balances changes in internal energy with heat and work under a stated sign convention. The second law limits the directions of spontaneous processes and the performance of energy-conversion devices. Heat engines, refrigerators, and heat pumps move energy through different arrangements, so their performance measures answer different questions. Entropy should be connected with those process constraints rather than used as a vague synonym for visible mess. An energy-flow diagram helps distinguish what enters a device, what it delivers, and what must leave elsewhere.

Study task. Sketch energy flows for a heat engine and a refrigerator. Explain why energy conservation alone is insufficient to determine whether a proposed device is physically possible.

Chapter 13 Waves and Their Properties

Waves carry disturbances and energy through space without requiring the medium’s particles to travel the entire distance with the disturbance. The chapter distinguishes wave types and relates speed, wavelength, frequency, period, and amplitude. These quantities describe different aspects of a pattern and should not be interchanged because they appear in the same equation. Superposition explains how overlapping waves combine, including constructive and destructive interference. A point in a medium oscillates while the pattern propagates, which is a useful distinction when interpreting drawings of a wave. The behaviour prepares the reader for sound, light, and later quantum descriptions.

Study task. Draw two wave patterns with the same wavelength but different amplitudes. Explain how their frequency and speed are related in the same nondispersive medium.

Chapter 14 Sound

Sound is a mechanical disturbance whose propagation depends on a medium. Its frequency relates to perceived pitch, while intensity and sound level describe energy transmission using different numerical scales. The Doppler effect changes the observed frequency when source and observer move relative to one another, without requiring the source’s vibration rate itself to change. Interference and resonance explain reinforcement, cancellation, and the response of vibrating systems. The chapter connects these ideas with familiar acoustic experiences but also asks readers to distinguish physical measurements from perception. A medium is necessary, so sound behaviour cannot be transferred unchanged to empty space.

Study task. Explain why a passing sound source changes perceived pitch. Compare this with resonance in a stationary system and identify which physical quantity changes in each explanation.

Chapter 15 Light

Light is placed within the wider electromagnetic spectrum, whose regions share a common physical basis while differing in wavelength and frequency. The chapter relates radiation’s behaviour to its interaction with materials, including transmission, absorption, and reflection. Different parts of the spectrum suit different applications because matter responds differently across those ranges. Frequency and wavelength are linked through propagation speed, but the properties of a medium must be considered when describing travel through matter. Understanding light as an electromagnetic wave connects the optical chapters with later electricity, magnetism, and quantum concepts instead of treating visible colours as an isolated topic.

Study task. Arrange several electromagnetic applications by wavelength or frequency. For each, explain what interaction with matter makes the application useful.

Chapter 16 Mirrors and Lenses

Geometrical optics models the paths of light rays through reflection and refraction. Mirrors and lenses form images whose positions and characteristics can be predicted with appropriate ray constructions and equations. A real image and a virtual image differ in whether light actually converges at the image location, not in whether the image can be seen. Sign conventions must be consistent when relating object distance, image distance, and focal length. Refraction depends on a change in propagation conditions, while the geometry determines the direction of bending. Drawing a small number of valid principal rays often clarifies an optical problem before any arithmetic is attempted.

Study task. Construct a ray diagram for one converging lens in two object positions. Compare image orientation, size, and whether the image is real or virtual.

Chapter 17 Diffraction and Interference

Diffraction and interference reveal light’s wave behaviour where a simple ray model is insufficient. Waves spread at openings and overlap to produce patterns determined by path differences and wavelength. Coherence provides the stable relationship needed for a persistent interference pattern. These ideas explain optical effects and technologies that cannot be understood merely by tracing isolated straight rays. The scale of the obstacle or opening relative to wavelength is central to deciding when wave effects become important. Readers should distinguish the existence of a wave phenomenon from the visibility of a particular pattern under the experimental conditions.

Study task. Predict qualitatively how a diffraction pattern changes when an opening becomes narrower. Explain why a ray diagram alone cannot capture the full pattern.

Chapter 18 Static Electricity

Electrostatics studies electric charge and the interactions associated with its distribution. Charge is conserved, and transfer changes how it is shared rather than creating an unlimited supply. Coulomb’s law describes the force between suitable charge models, while electric fields assign an influence to positions in space. Electric potential and potential energy provide a complementary energy-based description. Capacitors store separated charge and energy, with dielectrics influencing their behaviour. Distinguishing force, field, potential, and energy is a major conceptual goal: they are related but have different units and answer different questions. Diagrams help track both the direction of field effects and the signs of charges.

Study task. Compare electric field and electric potential near a simple charge arrangement. State what each quantity predicts for a test charge and why their units differ.

Chapter 19 Electrical Circuits

Circuit analysis follows the movement of charge and the transfer of electrical energy around connected components. Voltage, current, resistance, and power must be distinguished before applying their relationships. Series connections share a current, whereas parallel branches share a potential difference; the resulting equivalent resistance follows from those constraints. Charge conservation at junctions and energy accounting around a circuit explain why current is not simply used up by a resistor. Ohm’s law describes components that behave accordingly under the relevant conditions. Interpreting a circuit drawing as electrical connectivity, rather than as a literal map of wire shape, makes unfamiliar arrangements easier to analyse.

Study task. Draw one series and one parallel resistor circuit. Predict how adding a resistor changes total resistance and current for the same ideal voltage supply.

Chapter 20 Magnetism

Magnetism connects fields with moving charges and currents. Magnetic force depends on direction as well as magnitude, and field-line diagrams help organize the geometry. Electromagnetic induction adds a dynamic link: changing magnetic flux can produce an induced electrical effect. Motors, generators, and transformers use these relationships in different directions and arrangements to transfer energy. The chapter asks readers to connect the device’s physical motion or changing field with the resulting force or voltage. Keeping electric and magnetic explanations distinct while showing their connection prevents the common assumption that a static magnet provides unlimited electrical power.

Study task. Explain the energy input and output of a motor and a generator. Describe what must change to induce an electrical effect and identify the source of the transferred energy.

Chapter 21 The Quantum Nature of Light

Quantum descriptions of light address observations that a purely classical wave model cannot fully explain. Planck’s quantization connects radiation energy with discrete exchanges, while the photoelectric effect links electron emission with photon frequency and energy. Increasing intensity and increasing frequency can therefore have different consequences. The chapter also examines wave–particle duality: different experiments reveal aspects that cannot be captured by a simple everyday picture of either a tiny ball or a classical wave alone. The important step is to connect each model with the evidence it explains and the conditions under which its predictions are tested.

Study task. Compare increasing the intensity of light below a photoelectric threshold with increasing its frequency above that threshold. Explain why the outcomes differ.

Chapter 22 The Atom

Atomic and nuclear physics examine structures within matter and the interactions that hold or transform them. The chapter moves from atomic structure to nuclear forces, radioactive decay, half-life, fission, and fusion. Half-life describes a statistical pattern across a population of unstable nuclei rather than a timetable for one selected nucleus. Nuclear changes must be distinguished from ordinary chemical rearrangements, and their energy scales reflect a different process. Applications include radiometric dating and medical imaging or treatment, where the physical interaction and its purpose differ. Understanding the mechanism is essential before interpreting an application or making comparisons between radiation types.

Study task. Sketch a decay curve over several half-lives and explain what can and cannot be predicted for a single nucleus. Compare fission and fusion in terms of how nuclei change.

Chapter 23 Particle Physics

The final chapter asks how matter and interactions can be described at more fundamental scales. The four fundamental forces provide a framework for comparing gravitational, electromagnetic, strong, and weak interactions. Quarks extend the account beneath protons and neutrons, and particle classification replaces the assumption that every familiar material component is indivisible. The discussion of unification considers how apparently different phenomena may fit within a broader theoretical description. Readers should separate experimentally supported structure from the continuing research goal of a more unified account. The chapter completes the book’s progression from everyday motion to models of the smallest constituents of matter.

Study task. Make a comparison chart of the four fundamental interactions, then explain how the quark picture changes an earlier atomic model. Mark which parts describe established observations and which concern theoretical unification.

How to study this book

1. Begin each problem with a labelled diagram, system boundary, coordinate convention, and list of assumptions.
2. Identify the principle before choosing an equation: force balance, momentum conservation, energy transfer, wave behaviour, or another appropriate model.
3. Carry units through every calculation and use estimates or limiting cases to assess the result.
4. Translate one result per study session into a second representation, such as a graph, verbal explanation, or energy-flow diagram.
5. Use the source chapter reviews for retrieval practice. Rework errors after a delay rather than memorizing the printed solution.

Questions for reflection

• When does conservation of momentum simplify a problem more than a force calculation?
• How can choosing a different system boundary change an energy explanation?
• Which observations require a wave or quantum account rather than a geometrical-ray model?

Source edition and coverage

All twenty-three main chapters of the linked OpenStax Physics edition are covered. The guide follows that book’s sequence rather than the different sequence used by OpenStax College Physics. This original study guide explains the source in new wording and adds learning activities. Read the publisher’s book and complete exercises.