# High School Physics Center of Mass

Section 4: Momentum: Lecture 1 | 36:55 min

When we say a box exerts a force on the ground, what point on the box do we mean? If you were to crawl under the box so that a quarter of it were covering you, you wouldn’t feel all the weight of the box on you. That’s because the weight of an object is measured from its center, so that there’s as much of the object on the right as there is on the left as there is on top, etc. The concept of a center of mass is important in beginning our discussion on momentum as it’s an important concept to bear in mind as you solve problems involving linear momentum and collisions (like car crashes) in the next videos.

Vincent Selhorst-Jones

Center of Mass

Slide Duration:Table of Contents

16m 49s

- Intro0:00
- The Metric System0:26
- Distance, Mass, Volume, and Time0:27
- Scientific Notation1:40
- Examples: 47,000,000,000 and 0.000000021:41
- Significant Figures3:18
- Significant Figures Overview3:19
- Properties of Significant Figures4:04
- How Significant Figures Interact7:00
- Trigonometry Review8:57
- Pythagorean Theorem, sine, cosine, and tangent8:58
- Inverse Trigonometric Functions9:48
- Inverse Trigonometric Functions9:49
- Vectors10:44
- Vectors10:45
- Scalars12:10
- Scalars12:11
- Breaking a Vector into Components13:17
- Breaking a Vector into Components13:18
- Length of a Vector13:58
- Length of a Vector13:59
- Relationship Between Length, Angle, and Coordinates14:45

26m 2s

- Intro0:00
- Position0:06
- Definition and Example of Position0:07
- Distance1:11
- Definition and Example of Distance1:12
- Displacement1:34
- Definition and Example of Displacement1:35
- Comparison2:45
- Distance vs. Displacement2:46
- Notation2:54
- Notation for Location, Distance, and Displacement2:55
- Speed3:32
- Definition and Formula for Speed3:33
- Example: Speed3:51
- Velocity4:23
- Definition and Formula for Velocity4:24
- ∆ - Greek: 'Delta'5:01
- ∆ or 'Change In'5:02
- Acceleration6:02
- Definition and Formula for Acceleration6:03
- Example: Acceleration6:38
- Gravity7:31
- Gravity7:32
- Formulas8:44
- Kinematics Formula 18:45
- Kinematics Formula 29:32
- Definitional Formulas14:00
- Example 1: Speed of a Rock Being Thrown14:12
- Example 2: How Long Does It Take for the Rock to Hit the Ground?15:37
- Example 3: Acceleration of a Biker21:09
- Example 4: Velocity and Displacement of a UFO22:43

29m 59s

- Intro0:00
- What's Different About Multiple Dimensions?0:07
- Scalars and Vectors0:08
- A Note on Vectors2:12
- Indicating Vectors2:13
- Position3:03
- Position3:04
- Distance and Displacement3:35
- Distance and Displacement: Definitions3:36
- Distance and Displacement: Example4:39
- Speed and Velocity8:57
- Speed and Velocity: Definition & Formulas8:58
- Speed and Velocity: Example10:06
- Speed from Velocity12:01
- Speed from Velocity12:02
- Acceleration14:09
- Acceleration14:10
- Gravity14:26
- Gravity14:27
- Formulas15:11
- Formulas with Vectors15:12
- Example 1: Average Acceleration16:57
- Example 2A: Initial Velocity19:14
- Example 2B: How Long Does It Take for the Ball to Hit the Ground?21:35
- Example 2C: Displacement26:46

18m 36s

- Intro0:00
- Fundamental Example0:25
- Fundamental Example Part 10:26
- Fundamental Example Part 21:20
- General Case2:36
- Particle P and Two Observers A and B2:37
- Speed of P from A's Frame of Reference3:05
- What About Acceleration?3:22
- Acceleration Shows the Change in Velocity3:23
- Acceleration when Velocity is Constant3:48
- Multi-Dimensional Case4:35
- Multi-Dimensional Case4:36
- Some Notes5:04
- Choosing the Frame of Reference5:05
- Example 1: What Velocity does the Ball have from the Frame of Reference of a Stationary Observer?7:27
- Example 2: Velocity, Speed, and Displacement9:26
- Example 3: Speed and Acceleration in the Reference Frame12:44

16m 34s

- Intro0:00
- Centripetal Acceleration1:21
- Centripetal Acceleration of a Rock Being Twirled Around on a String1:22
- Looking Closer: Instantaneous Velocity and Tangential Velocity2:35
- Magnitude of Acceleration3:55
- Centripetal Acceleration Formula5:14
- You Say You Want a Revolution6:11
- What is a Revolution?6:12
- How Long Does it Take to Complete One Revolution Around the Circle?6:51
- Example 1: Centripetal Acceleration of a Rock7:40
- Example 2: Magnitude of a Car's Acceleration While Turning9:20
- Example 3: Speed of a Point on the Edge of a US Quarter13:10

12m 37s

- Intro0:00
- Newton's First Law/ Law of Inertia2:45
- A Body's Velocity Remains Constant Unless Acted Upon by a Force2:46
- Mass & Inertia4:07
- Mass & Inertia4:08
- Mass & Volume5:49
- Mass & Volume5:50
- Mass & Weight7:08
- Mass & Weight7:09
- Example 1: The Speed of a Rocket8:47
- Example 2: Which of the Following Has More Inertia?10:06
- Example 3: Change in Inertia11:51

27m 5s

- Intro0:00
- Net Force1:42
- Consider a Block That is Pushed On Equally From Both Sides1:43
- What if One of the Forces was Greater Than the Other?2:29
- The Net Force is All the Forces Put Together2:43
- Newton's Second Law3:14
- Net Force = (Mass) x (Acceleration)3:15
- Units3:48
- The Units of Newton's Second Law3:49
- Free-Body Diagram5:34
- Free-Body Diagram5:35
- Special Forces: Gravity (Weight)8:05
- Force of Gravity8:06
- Special Forces: Normal Force9:22
- Normal Force9:23
- Special Forces: Tension10:34
- Tension10:35
- Example 1: Force and Acceleration12:19
- Example 2: A 5kg Block is Pushed by Five Forces13:24
- Example 3: A 10kg Block Resting On a Table is Tethered Over a Pulley to a Free-Hanging 2kg Block16:30

27m 47s

- Intro0:00
- Newton's 2nd Law in Multiple Dimensions0:12
- Newton's 2nd Law in Multiple Dimensions0:13
- Components0:52
- Components0:53
- Example: Force in Component Form1:02
- Special Forces2:39
- Review of Special Forces: Gravity, Normal Force, and Tension2:40
- Normal Forces3:35
- Why Do We Call It the Normal Forces?3:36
- Normal Forces on a Flat Horizontal and Vertical Surface5:00
- Normal Forces on an Incline6:05
- Example 1: A 5kg Block is Pushed By a Force of 3N to the North and a Force of 4N to the East10:22
- Example 2: A 20kg Block is On an Incline of 50° With a Rope Holding It In Place16:08
- Example 3: A 10kg Block is On an Incline of 20° Attached By Rope to a Free-hanging Block of 5kg20:50

42m 5s

- Intro0:00
- Block and Tackle Pulley System0:30
- A Single Pulley Lifting System0:31
- A Double Pulley Lifting System1:32
- A Quadruple Pulley Lifting System2:59
- Example 1: A Free-hanging, Massless String is Holding Up Three Objects of Unknown Mass4:40
- Example 2: An Object is Acted Upon by Three Forces10:23
- Example 3: A Chandelier is Suspended by a Cable From the Roof of an Elevator17:13
- Example 4: A 20kg Baboon Climbs a Massless Rope That is Attached to a 22kg Crate23:46
- Example 5: Two Blocks are Roped Together on Inclines of Different Angles33:17

16m 47s

- Intro0:00
- Newton's Third Law0:50
- Newton's Third Law0:51
- Everyday Examples1:24
- Hammer Hitting a Nail1:25
- Swimming2:08
- Car Driving2:35
- Walking3:15
- Note3:57
- Newton's Third Law Sometimes Doesn't Come Into Play When Solving Problems: Reason 13:58
- Newton's Third Law Sometimes Doesn't Come Into Play When Solving Problems: Reason 25:36
- Example 1: What Force Does the Moon Pull on Earth?7:04
- Example 2: An Astronaut in Deep Space Throwing a Wrench8:38
- Example 3: A Woman Sitting in a Bosun's Chair that is Hanging from a Rope that Runs Over a Frictionless Pulley12:51

50m 11s

- Intro0:00
- Introduction0:04
- Our Intuition - Materials0:30
- Our Intuition - Weight2:48
- Our Intuition - Normal Force3:45
- The Normal Force and Friction4:11
- Two Scenarios: Same Object, Same Surface, Different Orientations4:12
- Friction is Not About Weight6:36
- Friction as an Equation7:23
- Summing Up Friction7:24
- Friction as an Equation7:36
- The Direction of Friction10:33
- The Direction of Friction10:34
- A Quick Example11:16
- Which Block Will Accelerate Faster?11:17
- Static vs. Kinetic14:52
- Static vs. Kinetic14:53
- Static and Kinetic Coefficient of Friction16:31
- How to Use Static Friction17:40
- How to Use Static Friction17:41
- Some Examples of μs and μk19:51
- Some Examples of μs and μk19:52
- A Remark on Wheels22:19
- A Remark on Wheels22:20
- Example 1: Calculating μs and μk28:02
- Example 2: At What Angle Does the Block Begin to Slide?31:35
- Example 3: A Block is Against a Wall, Sliding Down36:30
- Example 4: Two Blocks Sitting Atop Each Other40:16

26m 45s

- Intro0:00
- Centripetal Force0:46
- Equations for Centripetal Force0:47
- Centripetal Force in Action1:26
- Where Does Centripetal Force Come From?2:39
- Where Does Centripetal Force Come From?2:40
- Centrifugal Force4:05
- Centrifugal Force Part 14:06
- Centrifugal Force Part 26:16
- Example 1: Part A - Centripetal Force On the Car8:12
- Example 1: Part B - Maximum Speed the Car Can Take the Turn At Without Slipping8:56
- Example 2: A Bucket Full of Water is Spun Around in a Vertical Circle15:13
- Example 3: A Rock is Spun Around in a Vertical Circle21:36

28m 34s

- Intro0:00
- Equivocation0:05
- Equivocation0:06
- Introduction to Work0:32
- Scenarios: 10kg Block on a Frictionless Table0:33
- Scenario: 2 Block of Different Masses2:52
- Work4:12
- Work and Force4:13
- Paralleled vs. Perpendicular4:46
- Work: A Formal Definition7:33
- An Alternate Formula9:00
- An Alternate Formula9:01
- Units10:40
- Unit for Work: Joule (J)10:41
- Example 1: Calculating Work of Force11:32
- Example 2: Work and the Force of Gravity12:48
- Example 3: A Moving Box & Force Pushing in the Opposite Direction15:11
- Example 4: Work and Forces with Directions18:06
- Example 5: Work and the Force of Gravity23:16

39m 7s

- Intro0:00
- Types of Energy0:04
- Types of Energy0:05
- Conservation of Energy1:12
- Conservation of Energy1:13
- What is Energy?4:23
- Energy4:24
- What is Work?5:01
- Work5:02
- Circular Definition, Much?5:46
- Circular Definition, Much?5:47
- Derivation of Kinetic Energy (Simplified)7:44
- Simplified Picture of Work7:45
- Consider the Following Three Formulas8:42
- Kinetic Energy Formula11:01
- Kinetic Energy Formula11:02
- Units11:54
- Units for Kinetic Energy11:55
- Conservation of Energy13:24
- Energy Cannot be Made or Destroyed, Only Transferred13:25
- Friction15:02
- How Does Friction Work?15:03
- Example 1: Velocity of a Block15:59
- Example 2: Energy Released During a Collision18:28
- Example 3: Speed of a Block22:22
- Example 4: Speed and Position of a Block26:22

28m 10s

- Intro0:00
- Why Is It Called Potential Energy?0:21
- Why Is It Called Potential Energy?0:22
- Introduction to Gravitational Potential Energy1:20
- Consider an Object Dropped from Ever-Increasing heights1:21
- Gravitational Potential Energy2:02
- Gravitational Potential Energy: Derivation2:03
- Gravitational Potential Energy: Formulas2:52
- Gravitational Potential Energy: Notes3:48
- Conservation of Energy5:50
- Conservation of Energy and Formula5:51
- Example 1: Speed of a Falling Rock6:31
- Example 2: Energy Lost to Air Drag10:58
- Example 3: Distance of a Sliding Block15:51
- Example 4: Swinging Acrobat21:32

44m 16s

- Intro0:00
- Introduction to Elastic Potential0:12
- Elastic Object0:13
- Spring Example1:11
- Hooke's Law3:27
- Hooke's Law3:28
- Example of Hooke's Law5:14
- Elastic Potential Energy Formula8:27
- Elastic Potential Energy Formula8:28
- Conservation of Energy10:17
- Conservation of Energy10:18
- You Ain't Seen Nothin' Yet12:12
- You Ain't Seen Nothin' Yet12:13
- Example 1: Spring-Launcher13:10
- Example 2: Compressed Spring18:34
- Example 3: A Block Dangling From a Massless Spring24:33
- Example 4: Finding the Spring Constant36:13

28m 54s

- Intro0:00
- Introduction to Power & Simple Machines0:06
- What's the Difference Between a Go-Kart, a Family Van, and a Racecar?0:07
- Consider the Idea of Climbing a Flight of Stairs1:13
- Power2:35
- P= W / t2:36
- Alternate Formulas2:59
- Alternate Formulas3:00
- Units4:24
- Units for Power: Watt, Horsepower, and Kilowatt-hour4:25
- Block and Tackle, Redux5:29
- Block and Tackle Systems5:30
- Machines in General9:44
- Levers9:45
- Ramps10:51
- Example 1: Power of Force12:22
- Example 2: Power &Lifting a Watermelon14:21
- Example 3: Work and Instantaneous Power16:05
- Example 4: Power and Acceleration of a Race car25:56

36m 55s

- Intro0:00
- Introduction to Center of Mass0:04
- Consider a Ball Tossed in the Air0:05
- Center of Mass1:27
- Definition of Center of Mass1:28
- Example of center of Mass2:13
- Center of Mass: Derivation4:21
- Center of Mass: Formula6:44
- Center of Mass: Formula, Multiple Dimensions8:15
- Center of Mass: Symmetry9:07
- Center of Mass: Non-Homogeneous11:00
- Center of Gravity12:09
- Center of Mass vs. Center of Gravity12:10
- Newton's Second Law and the Center of Mass14:35
- Newton's Second Law and the Center of Mass14:36
- Example 1: Finding The Center of Mass16:29
- Example 2: Finding The Center of Mass18:55
- Example 3: Finding The Center of Mass21:46
- Example 4: A Boy and His Mail28:31

22m 50s

- Intro0:00
- Introduction to Linear Momentum0:04
- Linear Momentum Overview0:05
- Consider the Scenarios0:45
- Linear Momentum1:45
- Definition of Linear Momentum1:46
- Impulse3:10
- Impulse3:11
- Relationship Between Impulse & Momentum4:27
- Relationship Between Impulse & Momentum4:28
- Why is It Linear Momentum?6:55
- Why is It Linear Momentum?6:56
- Example 1: Momentum of a Skateboard8:25
- Example 2: Impulse and Final Velocity8:57
- Example 3: Change in Linear Momentum and magnitude of the Impulse13:53
- Example 4: A Ball of Putty17:07

40m 55s

- Intro0:00
- Investigating Collisions0:45
- Momentum0:46
- Center of Mass1:26
- Derivation1:56
- Extending Idea of Momentum to a System1:57
- Impulse5:10
- Conservation of Linear Momentum6:14
- Conservation of Linear Momentum6:15
- Conservation and External Forces7:56
- Conservation and External Forces7:57
- Momentum Vs. Energy9:52
- Momentum Vs. Energy9:53
- Types of Collisions12:33
- Elastic12:34
- Inelastic12:54
- Completely Inelastic13:24
- Everyday Collisions and Atomic Collisions13:42
- Example 1: Impact of Two Cars14:07
- Example 2: Billiard Balls16:59
- Example 3: Elastic Collision23:52
- Example 4: Bullet's Velocity33:35

34m 53s

- Intro0:00
- Law of Universal Gravitation1:39
- Law of Universal Gravitation1:40
- Force of Gravity Equation2:14
- Gravitational Field5:38
- Gravitational Field Overview5:39
- Gravitational Field Equation6:32
- Orbits9:25
- Orbits9:26
- The 'Falling' Moon12:58
- The 'Falling' Moon12:59
- Example 1: Force of Gravity17:05
- Example 2: Gravitational Field on the Surface of Earth20:35
- Example 3: Orbits23:15
- Example 4: Neutron Star28:38

35m 35s

- Intro0:00
- Pulse1:00
- Introduction to Pulse1:01
- Wave1:59
- Wave Overview2:00
- Wave Types3:16
- Mechanical Waves3:17
- Electromagnetic Waves4:01
- Matter or Quantum Mechanical Waves4:43
- Transverse Waves5:12
- Longitudinal Waves6:24
- Wave Characteristics7:24
- Amplitude and Wavelength7:25
- Wave Speed (v)10:13
- Period (T)11:02
- Frequency (f)12:33
- v = λf14:51
- Wave Equation16:15
- Wave Equation16:16
- Angular Wave Number17:34
- Angular Frequency19:36
- Example 1: CPU Frequency24:35
- Example 2: Speed of Light, Wavelength, and Frequency26:11
- Example 3: Spacing of Grooves28:35
- Example 4: Wave Diagram31:21

52m 57s

- Intro0:00
- Superposition0:38
- Superposition0:39
- Interference1:31
- Interference1:32
- Visual Example: Two Positive Pulses2:33
- Visual Example: Wave4:02
- Phase of Cycle6:25
- Phase Shift7:31
- Phase Shift7:32
- Standing Waves9:59
- Introduction to Standing Waves10:00
- Visual Examples: Standing Waves, Node, and Antinode11:27
- Standing Waves and Wavelengths15:37
- Standing Waves and Resonant Frequency19:18
- Doppler Effect20:36
- When Emitter and Receiver are Still20:37
- When Emitter is Moving Towards You22:31
- When Emitter is Moving Away24:12
- Doppler Effect: Formula25:58
- Example 1: Superposed Waves30:00
- Example 2: Superposed and Fully Destructive Interference35:57
- Example 3: Standing Waves on a String40:45
- Example 4: Police Siren43:26
- Example Sounds: 800 Hz, 906.7 Hz, 715.8 Hz, and Slide 906.7 to 715.8 Hz48:49

36m 24s

- Intro0:00
- Speed of Sound1:26
- Speed of Sound1:27
- Pitch2:44
- High Pitch & Low Pitch2:45
- Normal Hearing3:45
- Infrasonic and Ultrasonic4:02
- Intensity4:54
- Intensity: I = P/A4:55
- Intensity of Sound as an Outwardly Radiating Sphere6:32
- Decibels9:09
- Human Threshold for Hearing9:10
- Decibel (dB)10:28
- Sound Level β11:53
- Loudness Examples13:44
- Loudness Examples13:45
- Beats15:41
- Beats & Frequency15:42
- Audio Examples of Beats17:04
- Sonic Boom20:21
- Sonic Boom20:22
- Example 1: Firework23:14
- Example 2: Intensity and Decibels24:48
- Example 3: Decibels28:24
- Example 4: Frequency of a Violin34:48

19m 38s

- Intro0:00
- The Speed of Light0:31
- Speed of Light in a Vacuum0:32
- Unique Properties of Light1:20
- Lightspeed!3:24
- Lightyear3:25
- Medium4:34
- Light & Medium4:35
- Electromagnetic Spectrum5:49
- Electromagnetic Spectrum Overview5:50
- Electromagnetic Wave Classifications7:05
- Long Radio Waves & Radio Waves7:06
- Microwave8:30
- Infrared and Visible Spectrum9:02
- Ultraviolet, X-rays, and Gamma Rays9:33
- So Much Left to Explore11:07
- So Much Left to Explore11:08
- Example 1: How Much Distance is in a Light-year?13:16
- Example 2: Electromagnetic Wave16:50
- Example 3: Radio Station & Wavelength17:55

42m 52s

- Intro0:00
- Fluid?0:48
- What Does It Mean to be a Fluid?0:49
- Density1:46
- What is Density?1:47
- Formula for Density: ρ = m/V2:25
- Pressure3:40
- Consider Two Equal Height Cylinders of Water with Different Areas3:41
- Definition and Formula for Pressure: p = F/A5:20
- Pressure at Depth7:02
- Pressure at Depth Overview7:03
- Free Body Diagram for Pressure in a Container of Fluid8:31
- Equations for Pressure at Depth10:29
- Absolute Pressure vs. Gauge Pressure12:31
- Absolute Pressure vs. Gauge Pressure12:32
- Why Does Gauge Pressure Matter?13:51
- Depth, Not Shape or Direction15:22
- Depth, Not Shape or Direction15:23
- Depth = Height18:27
- Depth = Height18:28
- Buoyancy19:44
- Buoyancy and the Buoyant Force19:45
- Archimedes' Principle21:09
- Archimedes' Principle21:10
- Wait! What About Pressure?22:30
- Wait! What About Pressure?22:31
- Example 1: Rock & Fluid23:47
- Example 2: Pressure of Water at the Top of the Reservoir28:01
- Example 3: Wood & Fluid31:47
- Example 4: Force of Air Inside a Cylinder36:20

34m 6s

- Intro0:00
- Absolute Zero1:50
- Absolute Zero1:51
- Kelvin2:25
- Kelvin2:26
- Heat vs. Temperature4:21
- Heat vs. Temperature4:22
- Heating Water5:32
- Heating Water5:33
- Specific Heat7:44
- Specific Heat: Q = cm(∆T)7:45
- Heat Transfer9:20
- Conduction9:24
- Convection10:26
- Radiation11:35
- Example 1: Converting Temperature13:21
- Example 2: Calories14:54
- Example 3: Thermal Energy19:00
- Example 4: Temperature When Mixture Comes to Equilibrium Part 120:45
- Example 4: Temperature When Mixture Comes to Equilibrium Part 224:55

44m 3s

- Intro0:00
- Linear Expansion1:06
- Linear Expansion: ∆L = Lα(∆T)1:07
- Volume Expansion2:34
- Volume Expansion: ∆V = Vβ(∆T)2:35
- Gas Expansion3:40
- Gas Expansion3:41
- The Mole5:43
- Conceptual Example5:44
- The Mole and Avogadro's Number7:30
- Ideal Gas Law9:22
- Ideal Gas Law: pV = nRT9:23
- p = Pressure of the Gas10:07
- V = Volume of the Gas10:34
- n = Number of Moles of Gas10:44
- R = Gas Constant10:58
- T = Temperature11:58
- A Note On Water12:21
- A Note On Water12:22
- Change of Phase15:55
- Change of Phase15:56
- Change of Phase and Pressure17:31
- Phase Diagram18:41
- Heat of Transformation20:38
- Heat of Transformation: Q = Lm20:39
- Example 1: Linear Expansion22:38
- Example 2: Explore Why β = 3α24:40
- Example 3: Ideal Gas Law31:38
- Example 4: Heat of Transformation38:03

27m 30s

- Intro0:00
- First Law of Thermodynamics1:11
- First Law of Thermodynamics1:12
- Engines2:25
- Conceptual Example: Consider a Piston2:26
- Second Law of Thermodynamics4:17
- Second Law of Thermodynamics4:18
- Entropy6:09
- Definition of Entropy6:10
- Conceptual Example of Entropy: Stick of Dynamite7:00
- Order to Disorder8:22
- Order and Disorder in a System8:23
- The Poets Got It Right10:20
- The Poets Got It Right10:21
- Engines in General11:21
- Engines in General11:22
- Efficiency12:06
- Measuring the Efficiency of a System12:07
- Carnot Engine ( A Limit to Efficiency)13:20
- Carnot Engine & Maximum Possible Efficiency13:21
- Example 1: Internal Energy15:15
- Example 2: Efficiency16:13
- Example 3: Second Law of Thermodynamics17:05
- Example 4: Maximum Efficiency20:10

41m 35s

- Intro0:00
- Charge1:04
- Overview of Charge1:05
- Positive and Negative Charges1:19
- A Simple Model of the Atom2:47
- Protons, Electrons, and Neutrons2:48
- Conservation of Charge4:47
- Conservation of Charge4:48
- Elementary Charge5:41
- Elementary Charge and the Unit Coulomb5:42
- Coulomb's Law8:29
- Coulomb's Law & the Electrostatic Force8:30
- Coulomb's Law Breakdown9:30
- Conductors and Insulators11:11
- Conductors11:12
- Insulators12:31
- Conduction15:08
- Conduction15:09
- Conceptual Examples15:58
- Induction17:02
- Induction Overview17:01
- Conceptual Examples18:18
- Example 1: Electroscope20:08
- Example 2: Positive, Negative, and Net Charge of Iron22:15
- Example 3: Charge and Mass27:52
- Example 4: Two Metal Spheres31:58

34m 44s

- Intro0:00
- Electric Fields0:53
- Electric Fields Overview0:54
- Size of q2 (Second Charge)1:34
- Size of q1 (First Charge)1:53
- Electric Field Strength: Newtons Per Coulomb2:55
- Electric Field Lines4:19
- Electric Field Lines4:20
- Conceptual Example 15:17
- Conceptual Example 26:20
- Conceptual Example 36:59
- Conceptual Example 47:28
- Faraday Cage8:47
- Introduction to Faraday Cage8:48
- Why Does It Work?9:33
- Electric Potential Energy11:40
- Electric Potential Energy11:41
- Electric Potential13:44
- Electric Potential13:45
- Difference Between Two States14:29
- Electric Potential is Measured in Volts15:12
- Ground Voltage16:09
- Potential Differences and Reference Voltage16:10
- Ground Voltage17:20
- Electron-volt19:17
- Electron-volt19:18
- Equipotential Surfaces20:29
- Equipotential Surfaces20:30
- Equipotential Lines21:21
- Equipotential Lines21:22
- Example 1: Electric Field22:40
- Example 2: Change in Energy24:25
- Example 3: Constant Electrical Field27:06
- Example 4: Electrical Field and Change in Voltage29:06
- Example 5: Voltage and Energy32:14

29m 12s

- Intro0:00
- Electric Current0:31
- Electric Current0:32
- Amperes1:27
- Moving Charge1:52
- Conceptual Example: Electric Field and a Conductor1:53
- Voltage3:26
- Resistance5:05
- Given Some Voltage, How Much Current Will Flow?5:06
- Resistance: Definition and Formula5:40
- Resistivity7:31
- Resistivity7:32
- Resistance for a Uniform Object9:31
- Energy and Power9:55
- How Much Energy Does It take to Move These Charges Around?9:56
- What Do We Call Energy Per Unit Time?11:08
- Formulas to Express Electrical Power11:53
- Voltage Source13:38
- Introduction to Voltage Source13:39
- Obtaining a Voltage Source: Generator15:15
- Obtaining a Voltage Source: Battery16:19
- Speed of Electricity17:17
- Speed of Electricity17:18
- Example 1: Electric Current & Moving Charge19:40
- Example 2: Electric Current & Resistance20:31
- Example 3: Resistivity & Resistance21:56
- Example 4: Light Bulb25:16

52m 2s

- Intro0:00
- Electric Circuits0:51
- Current, Voltage, and Circuit0:52
- Resistor5:05
- Definition of Resistor5:06
- Conceptual Example: Lamps6:18
- Other Fundamental Components7:04
- Circuit Diagrams7:23
- Introduction to Circuit Diagrams7:24
- Wire7:42
- Resistor8:20
- Battery8:45
- Power Supply9:41
- Switch10:02
- Wires: Bypass and Connect10:53
- A Special Not in General12:04
- Example: Simple vs. Complex Circuit Diagram12:45
- Kirchoff's Circuit Laws15:32
- Kirchoff's Circuit Law 1: Current Law15:33
- Kirchoff's Circuit Law 1: Visual Example16:57
- Kirchoff's Circuit Law 2: Voltage Law17:16
- Kirchoff's Circuit Law 2: Visual Example19:23
- Resistors in Series21:48
- Resistors in Series21:49
- Resistors in Parallel23:33
- Resistors in Parallel23:34
- Voltmeter and Ammeter28:35
- Voltmeter28:36
- Ammeter30:05
- Direct Current vs. Alternating Current31:24
- Direct Current vs. Alternating Current31:25
- Visual Example: Voltage Graphs33:29
- Example 1: What Voltage is Read by the Voltmeter in This Diagram?33:57
- Example 2: What Current Flows Through the Ammeter When the Switch is Open?37:42
- Example 3: How Much Power is Dissipated by the Highlighted Resistor When the Switch is Open? When Closed?41:22
- Example 4: Design a Hallway Light Switch45:14

25m 47s

- Intro0:00
- Magnet1:27
- Magnet Has Two Poles1:28
- Magnetic Field1:47
- Always a Dipole, Never a Monopole2:22
- Always a Dipole, Never a Monopole2:23
- Magnetic Fields and Moving Charge4:01
- Magnetic Fields and Moving Charge4:02
- Magnets on an Atomic Level4:45
- Magnets on an Atomic Level4:46
- Evenly Distributed Motions5:45
- Unevenly Distributed Motions6:22
- Current and Magnetic Fields9:42
- Current Flow and Magnetic Field9:43
- Electromagnet11:35
- Electric Motor13:11
- Electric Motor13:12
- Generator15:38
- A Changing Magnetic Field Induces a Current15:39
- Example 1: What Kind of Magnetic Pole must the Earth's Geographic North Pole Be?19:34
- Example 2: Magnetic Field and Generator/Electric Motor20:56
- Example 3: Destroying the Magnetic Properties of a Permanent Magnet23:08

For more information, please see full course syllabus of High School Physics

1 answer

Last reply by: Professor Selhorst-Jones

Mon Oct 21, 2013 9:33 AM

Post by Robert Mills on October 20, 2013

On Example 4 Cont, talking about the boys new position, why is it that xr=xb+1, and not xr=xb+2, because the boat is 2m long? He's starting from the extreme opposite at 2m, walks to the other side, equalling 2 full meters. I'm probably just reading this all wrong, haha!