Dekorationsartikel gehören nicht zum Leistungsumfang.
Sprache:
Englisch
100,95 €*
Versandkostenfrei per Post / DHL
Lieferzeit 1-2 Wochen
Kategorien:
Beschreibung
Intended for algebra-based introductory physics courses.
Building on the research-proven instructional techniques introduced in KnightGÇÖs Physics for Scientists and Engineers, College Physics: A Strategic Approach sets a new standard for algebra-based introductory physicsGÇögaining widespread critical acclaim from professors and students alike. The text, supplements, and optional MasteringPhysics-« work together to help students see and understand the big picture, gain crucial problem-solving skills and confidence, and better prepare for lecture and their future.
For the 3rd Edition, Randy Knight, Brian Jones and Stuart Field have incorporated student feedback and research to strengthen their focus on student learning, and to apply the best results from educational research and extensive user feedback and metadata.
This program presents an unparalleled teaching and learning experience, uniquely effective and integrated.
Building on the research-proven instructional techniques introduced in KnightGÇÖs Physics for Scientists and Engineers, College Physics: A Strategic Approach sets a new standard for algebra-based introductory physicsGÇögaining widespread critical acclaim from professors and students alike. The text, supplements, and optional MasteringPhysics-« work together to help students see and understand the big picture, gain crucial problem-solving skills and confidence, and better prepare for lecture and their future.
For the 3rd Edition, Randy Knight, Brian Jones and Stuart Field have incorporated student feedback and research to strengthen their focus on student learning, and to apply the best results from educational research and extensive user feedback and metadata.
This program presents an unparalleled teaching and learning experience, uniquely effective and integrated.
- Prepare for lecture: Prepare students for lecture with innovative and engaging media tools, tailored carefully to reinforce the textbook.
- Understand the big picture: Enable students to understand the connections between topics, the real-world context, and the overarching themes, skills, and principles of physics using refined and expanded learning tools.
- Develop problem-solving skills: Equip students with problem-solving tactics and strategies through expanded guidance and practice in the text and online in MasteringPhysics.
- Foster skills for the MCAT: Gear students up for the new MCAT with enhanced life-science and biomedical applications in the text and problems, and increased emphasis on reasoning with real-world situations and data.
Intended for algebra-based introductory physics courses.
Building on the research-proven instructional techniques introduced in KnightGÇÖs Physics for Scientists and Engineers, College Physics: A Strategic Approach sets a new standard for algebra-based introductory physicsGÇögaining widespread critical acclaim from professors and students alike. The text, supplements, and optional MasteringPhysics-« work together to help students see and understand the big picture, gain crucial problem-solving skills and confidence, and better prepare for lecture and their future.
For the 3rd Edition, Randy Knight, Brian Jones and Stuart Field have incorporated student feedback and research to strengthen their focus on student learning, and to apply the best results from educational research and extensive user feedback and metadata.
This program presents an unparalleled teaching and learning experience, uniquely effective and integrated.
Building on the research-proven instructional techniques introduced in KnightGÇÖs Physics for Scientists and Engineers, College Physics: A Strategic Approach sets a new standard for algebra-based introductory physicsGÇögaining widespread critical acclaim from professors and students alike. The text, supplements, and optional MasteringPhysics-« work together to help students see and understand the big picture, gain crucial problem-solving skills and confidence, and better prepare for lecture and their future.
For the 3rd Edition, Randy Knight, Brian Jones and Stuart Field have incorporated student feedback and research to strengthen their focus on student learning, and to apply the best results from educational research and extensive user feedback and metadata.
This program presents an unparalleled teaching and learning experience, uniquely effective and integrated.
- Prepare for lecture: Prepare students for lecture with innovative and engaging media tools, tailored carefully to reinforce the textbook.
- Understand the big picture: Enable students to understand the connections between topics, the real-world context, and the overarching themes, skills, and principles of physics using refined and expanded learning tools.
- Develop problem-solving skills: Equip students with problem-solving tactics and strategies through expanded guidance and practice in the text and online in MasteringPhysics.
- Foster skills for the MCAT: Gear students up for the new MCAT with enhanced life-science and biomedical applications in the text and problems, and increased emphasis on reasoning with real-world situations and data.
Inhaltsverzeichnis
- Full Version, All Chapters: Chs 1-30
- Volume 1: Chs 1-16
- Volume 2: Chs 17-30
- OVERVIEW The Science of Physics
- Representing Motion
- 1.1 Motion: A First Look
- 1.2 Models and Modeling
- 1.3 Position and Time: Putting Numbers on Nature
- 1.4 Velocity
- 1.5 A Sense of Scale: Significant Figures, Scientific Notation, and Units
- 1.6 Vectors and Motion: A First Look
- 1.7 Where Do We Go from Here?
- SUMMARY
- QUESTIONS AND PROBLEMS
- 2.1 Describing Motion
- 2.2 Uniform Motion
- 2.3 Instantaneous Velocity
- 2.4 Acceleration
- 2.5 Motion with Constant Acceleration
- 2.6 Solving One-Dimensional Motion Problems
- 2.7 Free Fall
- SUMMARY
- QUESTIONS AND PROBLEMS
- 3.1 Using Vectors
- 3.2 Coordinate Systems and Vector Components
- 3.3 Motion on a Ramp
- 3.4 Motion in Two Dimensions
- 3.5 Projectile Motion
- 3.6 Projectile Motion: Solving Problems
- 3.7 Circular Motion
- 3.8 Relative Motion
- SUMMARY
- QUESTIONS AND PROBLEMS
- 4.1 Motion and Forces
- 4.2 A Short Catalog of Forces
- 4.3 Identifying Forces
- 4.4 What Do Forces Do?
- 4.5 Newton's Second Law
- 4.6 Free-Body Diagrams
- 4.7 Newton's Third Law
- SUMMARY
- QUESTIONS AND PROBLEMS
- 5.1 Equilibrium
- 5.2 Dynamics and Newton's Second Law
- 5.3 Mass and Weight
- 5.4 Normal Forces
- 5.5 Friction
- 5.6 Drag
- 5.7 Interacting Objects
- 5.8 Ropes and Pulleys
- SUMMARY
- QUESTIONS AND PROBLEMS
- 6.1 Uniform Circular Motion
- 6.2 Dynamics of Uniform Circular Motion
- 6.3 Apparent Forces in Circular Motion
- 6.4 Circular Orbits and Weightlessness
- 6.5 Newton's Law of Gravity
- 6.6 Gravity and Orbits
- SUMMARY
- QUESTIONS AND PROBLEMS
- 7.1 Describing Circular and Rotational Motion
- 7.2 The Rotation of a Rigid Body
- 7.3 Torque
- 7.4 Gravitational Torque and the Center of Gravity
- 7.5 Rotational Dynamics and Moment of Inertia
- 7.6 Using Newton's Second Law for Rotation
- 7.7 Rolling Motion
- SUMMARY
- QUESTIONS AND PROBLEMS
- 8.1 Torque and Static Equilibrium
- 8.2 Stability and Balance
- 8.3 Springs and Hooke's Law
- 8.4 Stretching and Compressing Materials
- 8.5 Forces and Torques in the Body
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART I SUMMARY Force and Motion
- ONE STEP BEYOND Dark Matter and the Structure of the Universe
- PART I PROBLEMS
- OVERVIEW Why Some Things Stay the Same
- 9.1 Impulse
- 9.2 Momentum and the Impulse-Momentum Theorem
- 9.3 Solving Impulse and Momentum Problems
- 9.4 Conservation of Momentum
- 9.5 Inelastic Collisions
- 9.6 Momentum and Collisions in Two Dimensions
- 9.7 Angular Momentum
- SUMMARY
- QUESTIONS AND PROBLEMS
- 10.1 The Basic Energy Model
- 10.2 Work
- 10.3 Kinetic Energy
- 10.4 Potential Energy
- 10.5 Thermal Energy
- 10.6 Conservation of Energy
- 10.7 Energy Diagrams
- 10.8 Molecular Bonds and Chemical Energy
- 10.9 Energy in Collisions
- 10.10 Power
- SUMMARY
- QUESTIONS AND PROBLEMS
- 11.1 Transforming Energy
- 11.2 Energy in the Body
- 11.3 Temperature, Thermal Energy, and Heat
- 11.4 The First Law of Thermodynamics
- 11.5 Heat Engines
- 11.6 Heat Pumps
- 11.7 Entropy and the Second Law of Thermodynamics
- 11.8 Systems, Energy, and Entropy
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART II SUMMARY Conservation Laws
- ONE STEP BEYOND Order Out of Chaos
- PART II PROBLEMS
- OVERVIEW Beyond the Particle Model
- 12.1 The Atomic Model of Matter
- 12.2 The Atomic Model of an Ideal Gas
- 12.3 Ideal-Gas Processes
- 12.4 Thermal Expansion
- 12.5 Specific Heat and Heat of Transformation
- 12.6 Calorimetry
- 12.7 Specific Heats of Gases
- 12.8 Heat Transfer
- 12.9 Diffusion
- SUMMARY
- QUESTIONS AND PROBLEMS
- 13.1 Fluids and Density
- 13.2 Pressure
- 13.3 Buoyancy
- 13.4 Fluids in Motion
- 13.5 Fluid Dynamics
- 13.6 Viscosity and Poiseuille's Equation
- 13.7 The Circulatory System
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART III SUMMARY Properties of Matter
- ONE STEP BEYOND Size and Life
- PART III PROBLEMS
- OVERVIEW Motion That Repeats Again and Again
- 14.1 Equilibrium and Oscillation
- 14.2 Linear Restoring Forces and SHM
- 14.3 Describing Simple Harmonic Motion
- 14.4 Energy in Simple Harmonic Motion
- 14.5 Pendulum Motion
- 14.6 Damped Oscillations
- 14.7 Driven Oscillations and Resonance
- SUMMARY
- QUESTIONS AND PROBLEMS
- 15.1 The Wave Model
- 15.2 Traveling Waves
- 15.3 Graphical and Mathematical Descriptions of Waves
- 15.4 Sound and Light Waves
- 15.5 Energy and Intensity
- 15.6 Loudness of Sound
- 15.7 The Doppler Effect and Shock Waves
- SUMMARY
- QUESTIONS AND PROBLEMS
- 16.1 The Principle of Superposition
- 16.2 Standing Waves
- 16.3 Standing Waves on a String
- 16.4 Standing Sound Waves
- 16.5 Speech and Hearing
- 16.6 The Interference of Waves from Two Sources
- 16.7 Beats
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART IV SUMMARY Oscillations and Waves
- ONE STEP BEYOND Waves in the Earth and the Ocean
- PART IV PROBLEMS
- OVERVIEW Light Is a Wave
- 17.1 What Is Light?
- 17.2 The Interference of Light
- 17.3 The Diffraction Grating
- 17.4 Thin-Film Interference
- 17.5 Single-Slit Diffraction
- 17.6 Circular-Aperture Diffraction
- SUMMARY
- QUESTIONS AND PROBLEMS
- 18.1 The Ray Model of Light
- 18.2 Reflection
- 18.3 Refraction
- 18.4 Image Formation by Refraction
- 18.5 Thin Lenses: Ray Tracing
- 18.6 Image Formation with Spherical Mirrors
- 18.7 The Thin-Lens Equation
- SUMMARY
- QUESTIONS AND PROBLEMS
- 19.1 The Camera
- 19.2 The Human Eye
- 19.3 The Magnifier
- 19.4 The Microscope
- 19.5 The Telescope
- 19.6 Color and Dispersion
- 19.7 Resolution of Optical Instruments
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART V SUMMARY Optics
- ONE STEP BEYOND Scanning Confocal Microscopy
- PART V PROBLEMS
- OVERVIEW Charges, Currents, and Fields
- 20.1 Charges and Forces
- 20.2 Charges, Atoms, and Molecules
- 20.3 Coulomb's Law
- 20.4 The Concept of the Electric Field
- 20.5 The Electric Field from Arrangements of Charges
- 20.6 Conductors and Electric Fields
- 20.7 Forces and Torques in Electric Fields
- SUMMARY
- QUESTIONS AND PROBLEMS
- 21.1 Electric Potential Energy and Electric Potential
- 21.2 Sources of Electric Potential
- 21.3 Electric Potential and Conservation of Energy
- 21.4 Calculating the Electric Potential
- 21.5 Connecting Potential and Field
- 21.6 The Electrocardiogram
- 21.7 Capacitance and Capacitors
- 21.8 Energy and Capacitors
- SUMMARY
- QUESTIONS AND PROBLEMS
- 22.1 A Model of Current
- 22.2 Defining and Describing Current
- 22.3 Batteries and emf
- 22.4 Connecting Potential and Current
- 22.5 Ohm's Law and Resistor Circuits
- 22.6 Energy and Power
- SUMMARY
- QUESTIONS AND PROBLEMS
- 23.1 Circuit Elements and Diagrams
- 23.2 Kirchhoff's Laws
- 23.3 Series and Parallel Circuits
- 23.4 Measuring Voltage and Current
- 23.5 More Complex Circuits
- 23.6 Capacitors in Parallel and Series
- 23.7 RC Circuits
- 23.8 Electricity in the Nervous System
- SUMMARY
- QUESTIONS AND PROBLEMS
- 24.1 Magnetism
- 24.2 The Magnetic Field
- 24.3 Electric Currents Also Create Magnetic Fields
- 24.4 Calculating...
Details
Erscheinungsjahr: | 2021 |
---|---|
Fachbereich: | Astronomie |
Genre: | Importe, Physik |
Rubrik: | Naturwissenschaften & Technik |
Medium: | Taschenbuch |
Inhalt: | Kartoniert / Broschiert |
ISBN-13: | 9781292277769 |
ISBN-10: | 1292277769 |
Sprache: | Englisch |
Einband: | Kartoniert / Broschiert |
Autor: |
Jones, Brian
Knight, Randall Field, Stuart |
Hersteller: | Pearson Education Limited |
Verantwortliche Person für die EU: | preigu, Ansas Meyer, Lengericher Landstr. 19, D-49078 Osnabrück, mail@preigu.de |
Maße: | 215 x 275 x 46 mm |
Von/Mit: | Brian Jones (u. a.) |
Erscheinungsdatum: | 16.06.2021 |
Gewicht: | 2,42 kg |
Inhaltsverzeichnis
- Full Version, All Chapters: Chs 1-30
- Volume 1: Chs 1-16
- Volume 2: Chs 17-30
- OVERVIEW The Science of Physics
- Representing Motion
- 1.1 Motion: A First Look
- 1.2 Models and Modeling
- 1.3 Position and Time: Putting Numbers on Nature
- 1.4 Velocity
- 1.5 A Sense of Scale: Significant Figures, Scientific Notation, and Units
- 1.6 Vectors and Motion: A First Look
- 1.7 Where Do We Go from Here?
- SUMMARY
- QUESTIONS AND PROBLEMS
- 2.1 Describing Motion
- 2.2 Uniform Motion
- 2.3 Instantaneous Velocity
- 2.4 Acceleration
- 2.5 Motion with Constant Acceleration
- 2.6 Solving One-Dimensional Motion Problems
- 2.7 Free Fall
- SUMMARY
- QUESTIONS AND PROBLEMS
- 3.1 Using Vectors
- 3.2 Coordinate Systems and Vector Components
- 3.3 Motion on a Ramp
- 3.4 Motion in Two Dimensions
- 3.5 Projectile Motion
- 3.6 Projectile Motion: Solving Problems
- 3.7 Circular Motion
- 3.8 Relative Motion
- SUMMARY
- QUESTIONS AND PROBLEMS
- 4.1 Motion and Forces
- 4.2 A Short Catalog of Forces
- 4.3 Identifying Forces
- 4.4 What Do Forces Do?
- 4.5 Newton's Second Law
- 4.6 Free-Body Diagrams
- 4.7 Newton's Third Law
- SUMMARY
- QUESTIONS AND PROBLEMS
- 5.1 Equilibrium
- 5.2 Dynamics and Newton's Second Law
- 5.3 Mass and Weight
- 5.4 Normal Forces
- 5.5 Friction
- 5.6 Drag
- 5.7 Interacting Objects
- 5.8 Ropes and Pulleys
- SUMMARY
- QUESTIONS AND PROBLEMS
- 6.1 Uniform Circular Motion
- 6.2 Dynamics of Uniform Circular Motion
- 6.3 Apparent Forces in Circular Motion
- 6.4 Circular Orbits and Weightlessness
- 6.5 Newton's Law of Gravity
- 6.6 Gravity and Orbits
- SUMMARY
- QUESTIONS AND PROBLEMS
- 7.1 Describing Circular and Rotational Motion
- 7.2 The Rotation of a Rigid Body
- 7.3 Torque
- 7.4 Gravitational Torque and the Center of Gravity
- 7.5 Rotational Dynamics and Moment of Inertia
- 7.6 Using Newton's Second Law for Rotation
- 7.7 Rolling Motion
- SUMMARY
- QUESTIONS AND PROBLEMS
- 8.1 Torque and Static Equilibrium
- 8.2 Stability and Balance
- 8.3 Springs and Hooke's Law
- 8.4 Stretching and Compressing Materials
- 8.5 Forces and Torques in the Body
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART I SUMMARY Force and Motion
- ONE STEP BEYOND Dark Matter and the Structure of the Universe
- PART I PROBLEMS
- OVERVIEW Why Some Things Stay the Same
- 9.1 Impulse
- 9.2 Momentum and the Impulse-Momentum Theorem
- 9.3 Solving Impulse and Momentum Problems
- 9.4 Conservation of Momentum
- 9.5 Inelastic Collisions
- 9.6 Momentum and Collisions in Two Dimensions
- 9.7 Angular Momentum
- SUMMARY
- QUESTIONS AND PROBLEMS
- 10.1 The Basic Energy Model
- 10.2 Work
- 10.3 Kinetic Energy
- 10.4 Potential Energy
- 10.5 Thermal Energy
- 10.6 Conservation of Energy
- 10.7 Energy Diagrams
- 10.8 Molecular Bonds and Chemical Energy
- 10.9 Energy in Collisions
- 10.10 Power
- SUMMARY
- QUESTIONS AND PROBLEMS
- 11.1 Transforming Energy
- 11.2 Energy in the Body
- 11.3 Temperature, Thermal Energy, and Heat
- 11.4 The First Law of Thermodynamics
- 11.5 Heat Engines
- 11.6 Heat Pumps
- 11.7 Entropy and the Second Law of Thermodynamics
- 11.8 Systems, Energy, and Entropy
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART II SUMMARY Conservation Laws
- ONE STEP BEYOND Order Out of Chaos
- PART II PROBLEMS
- OVERVIEW Beyond the Particle Model
- 12.1 The Atomic Model of Matter
- 12.2 The Atomic Model of an Ideal Gas
- 12.3 Ideal-Gas Processes
- 12.4 Thermal Expansion
- 12.5 Specific Heat and Heat of Transformation
- 12.6 Calorimetry
- 12.7 Specific Heats of Gases
- 12.8 Heat Transfer
- 12.9 Diffusion
- SUMMARY
- QUESTIONS AND PROBLEMS
- 13.1 Fluids and Density
- 13.2 Pressure
- 13.3 Buoyancy
- 13.4 Fluids in Motion
- 13.5 Fluid Dynamics
- 13.6 Viscosity and Poiseuille's Equation
- 13.7 The Circulatory System
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART III SUMMARY Properties of Matter
- ONE STEP BEYOND Size and Life
- PART III PROBLEMS
- OVERVIEW Motion That Repeats Again and Again
- 14.1 Equilibrium and Oscillation
- 14.2 Linear Restoring Forces and SHM
- 14.3 Describing Simple Harmonic Motion
- 14.4 Energy in Simple Harmonic Motion
- 14.5 Pendulum Motion
- 14.6 Damped Oscillations
- 14.7 Driven Oscillations and Resonance
- SUMMARY
- QUESTIONS AND PROBLEMS
- 15.1 The Wave Model
- 15.2 Traveling Waves
- 15.3 Graphical and Mathematical Descriptions of Waves
- 15.4 Sound and Light Waves
- 15.5 Energy and Intensity
- 15.6 Loudness of Sound
- 15.7 The Doppler Effect and Shock Waves
- SUMMARY
- QUESTIONS AND PROBLEMS
- 16.1 The Principle of Superposition
- 16.2 Standing Waves
- 16.3 Standing Waves on a String
- 16.4 Standing Sound Waves
- 16.5 Speech and Hearing
- 16.6 The Interference of Waves from Two Sources
- 16.7 Beats
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART IV SUMMARY Oscillations and Waves
- ONE STEP BEYOND Waves in the Earth and the Ocean
- PART IV PROBLEMS
- OVERVIEW Light Is a Wave
- 17.1 What Is Light?
- 17.2 The Interference of Light
- 17.3 The Diffraction Grating
- 17.4 Thin-Film Interference
- 17.5 Single-Slit Diffraction
- 17.6 Circular-Aperture Diffraction
- SUMMARY
- QUESTIONS AND PROBLEMS
- 18.1 The Ray Model of Light
- 18.2 Reflection
- 18.3 Refraction
- 18.4 Image Formation by Refraction
- 18.5 Thin Lenses: Ray Tracing
- 18.6 Image Formation with Spherical Mirrors
- 18.7 The Thin-Lens Equation
- SUMMARY
- QUESTIONS AND PROBLEMS
- 19.1 The Camera
- 19.2 The Human Eye
- 19.3 The Magnifier
- 19.4 The Microscope
- 19.5 The Telescope
- 19.6 Color and Dispersion
- 19.7 Resolution of Optical Instruments
- SUMMARY
- QUESTIONS AND PROBLEMS
- PART V SUMMARY Optics
- ONE STEP BEYOND Scanning Confocal Microscopy
- PART V PROBLEMS
- OVERVIEW Charges, Currents, and Fields
- 20.1 Charges and Forces
- 20.2 Charges, Atoms, and Molecules
- 20.3 Coulomb's Law
- 20.4 The Concept of the Electric Field
- 20.5 The Electric Field from Arrangements of Charges
- 20.6 Conductors and Electric Fields
- 20.7 Forces and Torques in Electric Fields
- SUMMARY
- QUESTIONS AND PROBLEMS
- 21.1 Electric Potential Energy and Electric Potential
- 21.2 Sources of Electric Potential
- 21.3 Electric Potential and Conservation of Energy
- 21.4 Calculating the Electric Potential
- 21.5 Connecting Potential and Field
- 21.6 The Electrocardiogram
- 21.7 Capacitance and Capacitors
- 21.8 Energy and Capacitors
- SUMMARY
- QUESTIONS AND PROBLEMS
- 22.1 A Model of Current
- 22.2 Defining and Describing Current
- 22.3 Batteries and emf
- 22.4 Connecting Potential and Current
- 22.5 Ohm's Law and Resistor Circuits
- 22.6 Energy and Power
- SUMMARY
- QUESTIONS AND PROBLEMS
- 23.1 Circuit Elements and Diagrams
- 23.2 Kirchhoff's Laws
- 23.3 Series and Parallel Circuits
- 23.4 Measuring Voltage and Current
- 23.5 More Complex Circuits
- 23.6 Capacitors in Parallel and Series
- 23.7 RC Circuits
- 23.8 Electricity in the Nervous System
- SUMMARY
- QUESTIONS AND PROBLEMS
- 24.1 Magnetism
- 24.2 The Magnetic Field
- 24.3 Electric Currents Also Create Magnetic Fields
- 24.4 Calculating...
Details
Erscheinungsjahr: | 2021 |
---|---|
Fachbereich: | Astronomie |
Genre: | Importe, Physik |
Rubrik: | Naturwissenschaften & Technik |
Medium: | Taschenbuch |
Inhalt: | Kartoniert / Broschiert |
ISBN-13: | 9781292277769 |
ISBN-10: | 1292277769 |
Sprache: | Englisch |
Einband: | Kartoniert / Broschiert |
Autor: |
Jones, Brian
Knight, Randall Field, Stuart |
Hersteller: | Pearson Education Limited |
Verantwortliche Person für die EU: | preigu, Ansas Meyer, Lengericher Landstr. 19, D-49078 Osnabrück, mail@preigu.de |
Maße: | 215 x 275 x 46 mm |
Von/Mit: | Brian Jones (u. a.) |
Erscheinungsdatum: | 16.06.2021 |
Gewicht: | 2,42 kg |
Sicherheitshinweis