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Vincent Selhorst-Jones

Vincent Selhorst-Jones

Newton's Third Law

Slide Duration:

Table of Contents

I. Motion
Math Review

16m 49s

Intro
0:00
The Metric System
0:26
Distance, Mass, Volume, and Time
0:27
Scientific Notation
1:40
Examples: 47,000,000,000 and 0.00000002
1:41
Significant Figures
3:18
Significant Figures Overview
3:19
Properties of Significant Figures
4:04
How Significant Figures Interact
7:00
Trigonometry Review
8:57
Pythagorean Theorem, sine, cosine, and tangent
8:58
Inverse Trigonometric Functions
9:48
Inverse Trigonometric Functions
9:49
Vectors
10:44
Vectors
10:45
Scalars
12:10
Scalars
12:11
Breaking a Vector into Components
13:17
Breaking a Vector into Components
13:18
Length of a Vector
13:58
Length of a Vector
13:59
Relationship Between Length, Angle, and Coordinates
14:45
One Dimensional Kinematics

26m 2s

Intro
0:00
Position
0:06
Definition and Example of Position
0:07
Distance
1:11
Definition and Example of Distance
1:12
Displacement
1:34
Definition and Example of Displacement
1:35
Comparison
2:45
Distance vs. Displacement
2:46
Notation
2:54
Notation for Location, Distance, and Displacement
2:55
Speed
3:32
Definition and Formula for Speed
3:33
Example: Speed
3:51
Velocity
4:23
Definition and Formula for Velocity
4:24
∆ - Greek: 'Delta'
5:01
∆ or 'Change In'
5:02
Acceleration
6:02
Definition and Formula for Acceleration
6:03
Example: Acceleration
6:38
Gravity
7:31
Gravity
7:32
Formulas
8:44
Kinematics Formula 1
8:45
Kinematics Formula 2
9:32
Definitional Formulas
14:00
Example 1: Speed of a Rock Being Thrown
14:12
Example 2: How Long Does It Take for the Rock to Hit the Ground?
15:37
Example 3: Acceleration of a Biker
21:09
Example 4: Velocity and Displacement of a UFO
22:43
Multi-Dimensional Kinematics

29m 59s

Intro
0:00
What's Different About Multiple Dimensions?
0:07
Scalars and Vectors
0:08
A Note on Vectors
2:12
Indicating Vectors
2:13
Position
3:03
Position
3:04
Distance and Displacement
3:35
Distance and Displacement: Definitions
3:36
Distance and Displacement: Example
4:39
Speed and Velocity
8:57
Speed and Velocity: Definition & Formulas
8:58
Speed and Velocity: Example
10:06
Speed from Velocity
12:01
Speed from Velocity
12:02
Acceleration
14:09
Acceleration
14:10
Gravity
14:26
Gravity
14:27
Formulas
15:11
Formulas with Vectors
15:12
Example 1: Average Acceleration
16:57
Example 2A: Initial Velocity
19:14
Example 2B: How Long Does It Take for the Ball to Hit the Ground?
21:35
Example 2C: Displacement
26:46
Frames of Reference

18m 36s

Intro
0:00
Fundamental Example
0:25
Fundamental Example Part 1
0:26
Fundamental Example Part 2
1:20
General Case
2:36
Particle P and Two Observers A and B
2:37
Speed of P from A's Frame of Reference
3:05
What About Acceleration?
3:22
Acceleration Shows the Change in Velocity
3:23
Acceleration when Velocity is Constant
3:48
Multi-Dimensional Case
4:35
Multi-Dimensional Case
4:36
Some Notes
5:04
Choosing the Frame of Reference
5:05
Example 1: What Velocity does the Ball have from the Frame of Reference of a Stationary Observer?
7:27
Example 2: Velocity, Speed, and Displacement
9:26
Example 3: Speed and Acceleration in the Reference Frame
12:44
Uniform Circular Motion

16m 34s

Intro
0:00
Centripetal Acceleration
1:21
Centripetal Acceleration of a Rock Being Twirled Around on a String
1:22
Looking Closer: Instantaneous Velocity and Tangential Velocity
2:35
Magnitude of Acceleration
3:55
Centripetal Acceleration Formula
5:14
You Say You Want a Revolution
6:11
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 Rock
7:40
Example 2: Magnitude of a Car's Acceleration While Turning
9:20
Example 3: Speed of a Point on the Edge of a US Quarter
13:10
II. Force
Newton's 1st Law

12m 37s

Intro
0:00
Newton's First Law/ Law of Inertia
2:45
A Body's Velocity Remains Constant Unless Acted Upon by a Force
2:46
Mass & Inertia
4:07
Mass & Inertia
4:08
Mass & Volume
5:49
Mass & Volume
5:50
Mass & Weight
7:08
Mass & Weight
7:09
Example 1: The Speed of a Rocket
8:47
Example 2: Which of the Following Has More Inertia?
10:06
Example 3: Change in Inertia
11:51
Newton's 2nd Law: Introduction

27m 5s

Intro
0:00
Net Force
1:42
Consider a Block That is Pushed On Equally From Both Sides
1:43
What if One of the Forces was Greater Than the Other?
2:29
The Net Force is All the Forces Put Together
2:43
Newton's Second Law
3:14
Net Force = (Mass) x (Acceleration)
3:15
Units
3:48
The Units of Newton's Second Law
3:49
Free-Body Diagram
5:34
Free-Body Diagram
5:35
Special Forces: Gravity (Weight)
8:05
Force of Gravity
8:06
Special Forces: Normal Force
9:22
Normal Force
9:23
Special Forces: Tension
10:34
Tension
10:35
Example 1: Force and Acceleration
12:19
Example 2: A 5kg Block is Pushed by Five Forces
13:24
Example 3: A 10kg Block Resting On a Table is Tethered Over a Pulley to a Free-Hanging 2kg Block
16:30
Newton's 2nd Law: Multiple Dimensions

27m 47s

Intro
0:00
Newton's 2nd Law in Multiple Dimensions
0:12
Newton's 2nd Law in Multiple Dimensions
0:13
Components
0:52
Components
0:53
Example: Force in Component Form
1:02
Special Forces
2:39
Review of Special Forces: Gravity, Normal Force, and Tension
2:40
Normal Forces
3:35
Why Do We Call It the Normal Forces?
3:36
Normal Forces on a Flat Horizontal and Vertical Surface
5:00
Normal Forces on an Incline
6:05
Example 1: A 5kg Block is Pushed By a Force of 3N to the North and a Force of 4N to the East
10:22
Example 2: A 20kg Block is On an Incline of 50° With a Rope Holding It In Place
16:08
Example 3: A 10kg Block is On an Incline of 20° Attached By Rope to a Free-hanging Block of 5kg
20:50
Newton's 2nd Law: Advanced Examples

42m 5s

Intro
0:00
Block and Tackle Pulley System
0:30
A Single Pulley Lifting System
0:31
A Double Pulley Lifting System
1:32
A Quadruple Pulley Lifting System
2:59
Example 1: A Free-hanging, Massless String is Holding Up Three Objects of Unknown Mass
4:40
Example 2: An Object is Acted Upon by Three Forces
10:23
Example 3: A Chandelier is Suspended by a Cable From the Roof of an Elevator
17:13
Example 4: A 20kg Baboon Climbs a Massless Rope That is Attached to a 22kg Crate
23:46
Example 5: Two Blocks are Roped Together on Inclines of Different Angles
33:17
Newton's Third Law

16m 47s

Intro
0:00
Newton's Third Law
0:50
Newton's Third Law
0:51
Everyday Examples
1:24
Hammer Hitting a Nail
1:25
Swimming
2:08
Car Driving
2:35
Walking
3:15
Note
3:57
Newton's Third Law Sometimes Doesn't Come Into Play When Solving Problems: Reason 1
3:58
Newton's Third Law Sometimes Doesn't Come Into Play When Solving Problems: Reason 2
5:36
Example 1: What Force Does the Moon Pull on Earth?
7:04
Example 2: An Astronaut in Deep Space Throwing a Wrench
8:38
Example 3: A Woman Sitting in a Bosun's Chair that is Hanging from a Rope that Runs Over a Frictionless Pulley
12:51
Friction

50m 11s

Intro
0:00
Introduction
0:04
Our Intuition - Materials
0:30
Our Intuition - Weight
2:48
Our Intuition - Normal Force
3:45
The Normal Force and Friction
4:11
Two Scenarios: Same Object, Same Surface, Different Orientations
4:12
Friction is Not About Weight
6:36
Friction as an Equation
7:23
Summing Up Friction
7:24
Friction as an Equation
7:36
The Direction of Friction
10:33
The Direction of Friction
10:34
A Quick Example
11:16
Which Block Will Accelerate Faster?
11:17
Static vs. Kinetic
14:52
Static vs. Kinetic
14:53
Static and Kinetic Coefficient of Friction
16:31
How to Use Static Friction
17:40
How to Use Static Friction
17:41
Some Examples of μs and μk
19:51
Some Examples of μs and μk
19:52
A Remark on Wheels
22:19
A Remark on Wheels
22:20
Example 1: Calculating μs and μk
28:02
Example 2: At What Angle Does the Block Begin to Slide?
31:35
Example 3: A Block is Against a Wall, Sliding Down
36:30
Example 4: Two Blocks Sitting Atop Each Other
40:16
Force & Uniform Circular Motion

26m 45s

Intro
0:00
Centripetal Force
0:46
Equations for Centripetal Force
0:47
Centripetal Force in Action
1:26
Where Does Centripetal Force Come From?
2:39
Where Does Centripetal Force Come From?
2:40
Centrifugal Force
4:05
Centrifugal Force Part 1
4:06
Centrifugal Force Part 2
6:16
Example 1: Part A - Centripetal Force On the Car
8:12
Example 1: Part B - Maximum Speed the Car Can Take the Turn At Without Slipping
8:56
Example 2: A Bucket Full of Water is Spun Around in a Vertical Circle
15:13
Example 3: A Rock is Spun Around in a Vertical Circle
21:36
III. Energy
Work

28m 34s

Intro
0:00
Equivocation
0:05
Equivocation
0:06
Introduction to Work
0:32
Scenarios: 10kg Block on a Frictionless Table
0:33
Scenario: 2 Block of Different Masses
2:52
Work
4:12
Work and Force
4:13
Paralleled vs. Perpendicular
4:46
Work: A Formal Definition
7:33
An Alternate Formula
9:00
An Alternate Formula
9:01
Units
10:40
Unit for Work: Joule (J)
10:41
Example 1: Calculating Work of Force
11:32
Example 2: Work and the Force of Gravity
12:48
Example 3: A Moving Box & Force Pushing in the Opposite Direction
15:11
Example 4: Work and Forces with Directions
18:06
Example 5: Work and the Force of Gravity
23:16
Energy: Kinetic

39m 7s

Intro
0:00
Types of Energy
0:04
Types of Energy
0:05
Conservation of Energy
1:12
Conservation of Energy
1:13
What is Energy?
4:23
Energy
4:24
What is Work?
5:01
Work
5:02
Circular Definition, Much?
5:46
Circular Definition, Much?
5:47
Derivation of Kinetic Energy (Simplified)
7:44
Simplified Picture of Work
7:45
Consider the Following Three Formulas
8:42
Kinetic Energy Formula
11:01
Kinetic Energy Formula
11:02
Units
11:54
Units for Kinetic Energy
11:55
Conservation of Energy
13:24
Energy Cannot be Made or Destroyed, Only Transferred
13:25
Friction
15:02
How Does Friction Work?
15:03
Example 1: Velocity of a Block
15:59
Example 2: Energy Released During a Collision
18:28
Example 3: Speed of a Block
22:22
Example 4: Speed and Position of a Block
26:22
Energy: Gravitational Potential

28m 10s

Intro
0:00
Why Is It Called Potential Energy?
0:21
Why Is It Called Potential Energy?
0:22
Introduction to Gravitational Potential Energy
1:20
Consider an Object Dropped from Ever-Increasing heights
1:21
Gravitational Potential Energy
2:02
Gravitational Potential Energy: Derivation
2:03
Gravitational Potential Energy: Formulas
2:52
Gravitational Potential Energy: Notes
3:48
Conservation of Energy
5:50
Conservation of Energy and Formula
5:51
Example 1: Speed of a Falling Rock
6:31
Example 2: Energy Lost to Air Drag
10:58
Example 3: Distance of a Sliding Block
15:51
Example 4: Swinging Acrobat
21:32
Energy: Elastic Potential

44m 16s

Intro
0:00
Introduction to Elastic Potential
0:12
Elastic Object
0:13
Spring Example
1:11
Hooke's Law
3:27
Hooke's Law
3:28
Example of Hooke's Law
5:14
Elastic Potential Energy Formula
8:27
Elastic Potential Energy Formula
8:28
Conservation of Energy
10:17
Conservation of Energy
10:18
You Ain't Seen Nothin' Yet
12:12
You Ain't Seen Nothin' Yet
12:13
Example 1: Spring-Launcher
13:10
Example 2: Compressed Spring
18:34
Example 3: A Block Dangling From a Massless Spring
24:33
Example 4: Finding the Spring Constant
36:13
Power & Simple Machines

28m 54s

Intro
0:00
Introduction to Power & Simple Machines
0:06
What's the Difference Between a Go-Kart, a Family Van, and a Racecar?
0:07
Consider the Idea of Climbing a Flight of Stairs
1:13
Power
2:35
P= W / t
2:36
Alternate Formulas
2:59
Alternate Formulas
3:00
Units
4:24
Units for Power: Watt, Horsepower, and Kilowatt-hour
4:25
Block and Tackle, Redux
5:29
Block and Tackle Systems
5:30
Machines in General
9:44
Levers
9:45
Ramps
10:51
Example 1: Power of Force
12:22
Example 2: Power &Lifting a Watermelon
14:21
Example 3: Work and Instantaneous Power
16:05
Example 4: Power and Acceleration of a Race car
25:56
IV. Momentum
Center of Mass

36m 55s

Intro
0:00
Introduction to Center of Mass
0:04
Consider a Ball Tossed in the Air
0:05
Center of Mass
1:27
Definition of Center of Mass
1:28
Example of center of Mass
2:13
Center of Mass: Derivation
4:21
Center of Mass: Formula
6:44
Center of Mass: Formula, Multiple Dimensions
8:15
Center of Mass: Symmetry
9:07
Center of Mass: Non-Homogeneous
11:00
Center of Gravity
12:09
Center of Mass vs. Center of Gravity
12:10
Newton's Second Law and the Center of Mass
14:35
Newton's Second Law and the Center of Mass
14:36
Example 1: Finding The Center of Mass
16:29
Example 2: Finding The Center of Mass
18:55
Example 3: Finding The Center of Mass
21:46
Example 4: A Boy and His Mail
28:31
Linear Momentum

22m 50s

Intro
0:00
Introduction to Linear Momentum
0:04
Linear Momentum Overview
0:05
Consider the Scenarios
0:45
Linear Momentum
1:45
Definition of Linear Momentum
1:46
Impulse
3:10
Impulse
3:11
Relationship Between Impulse & Momentum
4:27
Relationship Between Impulse & Momentum
4:28
Why is It Linear Momentum?
6:55
Why is It Linear Momentum?
6:56
Example 1: Momentum of a Skateboard
8:25
Example 2: Impulse and Final Velocity
8:57
Example 3: Change in Linear Momentum and magnitude of the Impulse
13:53
Example 4: A Ball of Putty
17:07
Collisions & Linear Momentum

40m 55s

Intro
0:00
Investigating Collisions
0:45
Momentum
0:46
Center of Mass
1:26
Derivation
1:56
Extending Idea of Momentum to a System
1:57
Impulse
5:10
Conservation of Linear Momentum
6:14
Conservation of Linear Momentum
6:15
Conservation and External Forces
7:56
Conservation and External Forces
7:57
Momentum Vs. Energy
9:52
Momentum Vs. Energy
9:53
Types of Collisions
12:33
Elastic
12:34
Inelastic
12:54
Completely Inelastic
13:24
Everyday Collisions and Atomic Collisions
13:42
Example 1: Impact of Two Cars
14:07
Example 2: Billiard Balls
16:59
Example 3: Elastic Collision
23:52
Example 4: Bullet's Velocity
33:35
V. Gravity
Gravity & Orbits

34m 53s

Intro
0:00
Law of Universal Gravitation
1:39
Law of Universal Gravitation
1:40
Force of Gravity Equation
2:14
Gravitational Field
5:38
Gravitational Field Overview
5:39
Gravitational Field Equation
6:32
Orbits
9:25
Orbits
9:26
The 'Falling' Moon
12:58
The 'Falling' Moon
12:59
Example 1: Force of Gravity
17:05
Example 2: Gravitational Field on the Surface of Earth
20:35
Example 3: Orbits
23:15
Example 4: Neutron Star
28:38
VI. Waves
Intro to Waves

35m 35s

Intro
0:00
Pulse
1:00
Introduction to Pulse
1:01
Wave
1:59
Wave Overview
2:00
Wave Types
3:16
Mechanical Waves
3:17
Electromagnetic Waves
4:01
Matter or Quantum Mechanical Waves
4:43
Transverse Waves
5:12
Longitudinal Waves
6:24
Wave Characteristics
7:24
Amplitude and Wavelength
7:25
Wave Speed (v)
10:13
Period (T)
11:02
Frequency (f)
12:33
v = λf
14:51
Wave Equation
16:15
Wave Equation
16:16
Angular Wave Number
17:34
Angular Frequency
19:36
Example 1: CPU Frequency
24:35
Example 2: Speed of Light, Wavelength, and Frequency
26:11
Example 3: Spacing of Grooves
28:35
Example 4: Wave Diagram
31:21
Waves, Cont.

52m 57s

Intro
0:00
Superposition
0:38
Superposition
0:39
Interference
1:31
Interference
1:32
Visual Example: Two Positive Pulses
2:33
Visual Example: Wave
4:02
Phase of Cycle
6:25
Phase Shift
7:31
Phase Shift
7:32
Standing Waves
9:59
Introduction to Standing Waves
10:00
Visual Examples: Standing Waves, Node, and Antinode
11:27
Standing Waves and Wavelengths
15:37
Standing Waves and Resonant Frequency
19:18
Doppler Effect
20:36
When Emitter and Receiver are Still
20:37
When Emitter is Moving Towards You
22:31
When Emitter is Moving Away
24:12
Doppler Effect: Formula
25:58
Example 1: Superposed Waves
30:00
Example 2: Superposed and Fully Destructive Interference
35:57
Example 3: Standing Waves on a String
40:45
Example 4: Police Siren
43:26
Example Sounds: 800 Hz, 906.7 Hz, 715.8 Hz, and Slide 906.7 to 715.8 Hz
48:49
Sound

36m 24s

Intro
0:00
Speed of Sound
1:26
Speed of Sound
1:27
Pitch
2:44
High Pitch & Low Pitch
2:45
Normal Hearing
3:45
Infrasonic and Ultrasonic
4:02
Intensity
4:54
Intensity: I = P/A
4:55
Intensity of Sound as an Outwardly Radiating Sphere
6:32
Decibels
9:09
Human Threshold for Hearing
9:10
Decibel (dB)
10:28
Sound Level β
11:53
Loudness Examples
13:44
Loudness Examples
13:45
Beats
15:41
Beats & Frequency
15:42
Audio Examples of Beats
17:04
Sonic Boom
20:21
Sonic Boom
20:22
Example 1: Firework
23:14
Example 2: Intensity and Decibels
24:48
Example 3: Decibels
28:24
Example 4: Frequency of a Violin
34:48
Light

19m 38s

Intro
0:00
The Speed of Light
0:31
Speed of Light in a Vacuum
0:32
Unique Properties of Light
1:20
Lightspeed!
3:24
Lightyear
3:25
Medium
4:34
Light & Medium
4:35
Electromagnetic Spectrum
5:49
Electromagnetic Spectrum Overview
5:50
Electromagnetic Wave Classifications
7:05
Long Radio Waves & Radio Waves
7:06
Microwave
8:30
Infrared and Visible Spectrum
9:02
Ultraviolet, X-rays, and Gamma Rays
9:33
So Much Left to Explore
11:07
So Much Left to Explore
11:08
Example 1: How Much Distance is in a Light-year?
13:16
Example 2: Electromagnetic Wave
16:50
Example 3: Radio Station & Wavelength
17:55
VII. Thermodynamics
Fluids

42m 52s

Intro
0:00
Fluid?
0:48
What Does It Mean to be a Fluid?
0:49
Density
1:46
What is Density?
1:47
Formula for Density: ρ = m/V
2:25
Pressure
3:40
Consider Two Equal Height Cylinders of Water with Different Areas
3:41
Definition and Formula for Pressure: p = F/A
5:20
Pressure at Depth
7:02
Pressure at Depth Overview
7:03
Free Body Diagram for Pressure in a Container of Fluid
8:31
Equations for Pressure at Depth
10:29
Absolute Pressure vs. Gauge Pressure
12:31
Absolute Pressure vs. Gauge Pressure
12:32
Why Does Gauge Pressure Matter?
13:51
Depth, Not Shape or Direction
15:22
Depth, Not Shape or Direction
15:23
Depth = Height
18:27
Depth = Height
18:28
Buoyancy
19:44
Buoyancy and the Buoyant Force
19:45
Archimedes' Principle
21:09
Archimedes' Principle
21:10
Wait! What About Pressure?
22:30
Wait! What About Pressure?
22:31
Example 1: Rock & Fluid
23:47
Example 2: Pressure of Water at the Top of the Reservoir
28:01
Example 3: Wood & Fluid
31:47
Example 4: Force of Air Inside a Cylinder
36:20
Intro to Temperature & Heat

34m 6s

Intro
0:00
Absolute Zero
1:50
Absolute Zero
1:51
Kelvin
2:25
Kelvin
2:26
Heat vs. Temperature
4:21
Heat vs. Temperature
4:22
Heating Water
5:32
Heating Water
5:33
Specific Heat
7:44
Specific Heat: Q = cm(∆T)
7:45
Heat Transfer
9:20
Conduction
9:24
Convection
10:26
Radiation
11:35
Example 1: Converting Temperature
13:21
Example 2: Calories
14:54
Example 3: Thermal Energy
19:00
Example 4: Temperature When Mixture Comes to Equilibrium Part 1
20:45
Example 4: Temperature When Mixture Comes to Equilibrium Part 2
24:55
Change Due to Heat

44m 3s

Intro
0:00
Linear Expansion
1:06
Linear Expansion: ∆L = Lα(∆T)
1:07
Volume Expansion
2:34
Volume Expansion: ∆V = Vβ(∆T)
2:35
Gas Expansion
3:40
Gas Expansion
3:41
The Mole
5:43
Conceptual Example
5:44
The Mole and Avogadro's Number
7:30
Ideal Gas Law
9:22
Ideal Gas Law: pV = nRT
9:23
p = Pressure of the Gas
10:07
V = Volume of the Gas
10:34
n = Number of Moles of Gas
10:44
R = Gas Constant
10:58
T = Temperature
11:58
A Note On Water
12:21
A Note On Water
12:22
Change of Phase
15:55
Change of Phase
15:56
Change of Phase and Pressure
17:31
Phase Diagram
18:41
Heat of Transformation
20:38
Heat of Transformation: Q = Lm
20:39
Example 1: Linear Expansion
22:38
Example 2: Explore Why β = 3α
24:40
Example 3: Ideal Gas Law
31:38
Example 4: Heat of Transformation
38:03
Thermodynamics

27m 30s

Intro
0:00
First Law of Thermodynamics
1:11
First Law of Thermodynamics
1:12
Engines
2:25
Conceptual Example: Consider a Piston
2:26
Second Law of Thermodynamics
4:17
Second Law of Thermodynamics
4:18
Entropy
6:09
Definition of Entropy
6:10
Conceptual Example of Entropy: Stick of Dynamite
7:00
Order to Disorder
8:22
Order and Disorder in a System
8:23
The Poets Got It Right
10:20
The Poets Got It Right
10:21
Engines in General
11:21
Engines in General
11:22
Efficiency
12:06
Measuring the Efficiency of a System
12:07
Carnot Engine ( A Limit to Efficiency)
13:20
Carnot Engine & Maximum Possible Efficiency
13:21
Example 1: Internal Energy
15:15
Example 2: Efficiency
16:13
Example 3: Second Law of Thermodynamics
17:05
Example 4: Maximum Efficiency
20:10
VIII. Electricity
Electric Force & Charge

41m 35s

Intro
0:00
Charge
1:04
Overview of Charge
1:05
Positive and Negative Charges
1:19
A Simple Model of the Atom
2:47
Protons, Electrons, and Neutrons
2:48
Conservation of Charge
4:47
Conservation of Charge
4:48
Elementary Charge
5:41
Elementary Charge and the Unit Coulomb
5:42
Coulomb's Law
8:29
Coulomb's Law & the Electrostatic Force
8:30
Coulomb's Law Breakdown
9:30
Conductors and Insulators
11:11
Conductors
11:12
Insulators
12:31
Conduction
15:08
Conduction
15:09
Conceptual Examples
15:58
Induction
17:02
Induction Overview
17:01
Conceptual Examples
18:18
Example 1: Electroscope
20:08
Example 2: Positive, Negative, and Net Charge of Iron
22:15
Example 3: Charge and Mass
27:52
Example 4: Two Metal Spheres
31:58
Electric Fields & Potential

34m 44s

Intro
0:00
Electric Fields
0:53
Electric Fields Overview
0:54
Size of q2 (Second Charge)
1:34
Size of q1 (First Charge)
1:53
Electric Field Strength: Newtons Per Coulomb
2:55
Electric Field Lines
4:19
Electric Field Lines
4:20
Conceptual Example 1
5:17
Conceptual Example 2
6:20
Conceptual Example 3
6:59
Conceptual Example 4
7:28
Faraday Cage
8:47
Introduction to Faraday Cage
8:48
Why Does It Work?
9:33
Electric Potential Energy
11:40
Electric Potential Energy
11:41
Electric Potential
13:44
Electric Potential
13:45
Difference Between Two States
14:29
Electric Potential is Measured in Volts
15:12
Ground Voltage
16:09
Potential Differences and Reference Voltage
16:10
Ground Voltage
17:20
Electron-volt
19:17
Electron-volt
19:18
Equipotential Surfaces
20:29
Equipotential Surfaces
20:30
Equipotential Lines
21:21
Equipotential Lines
21:22
Example 1: Electric Field
22:40
Example 2: Change in Energy
24:25
Example 3: Constant Electrical Field
27:06
Example 4: Electrical Field and Change in Voltage
29:06
Example 5: Voltage and Energy
32:14
Electric Current

29m 12s

Intro
0:00
Electric Current
0:31
Electric Current
0:32
Amperes
1:27
Moving Charge
1:52
Conceptual Example: Electric Field and a Conductor
1:53
Voltage
3:26
Resistance
5:05
Given Some Voltage, How Much Current Will Flow?
5:06
Resistance: Definition and Formula
5:40
Resistivity
7:31
Resistivity
7:32
Resistance for a Uniform Object
9:31
Energy and Power
9:55
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 Power
11:53
Voltage Source
13:38
Introduction to Voltage Source
13:39
Obtaining a Voltage Source: Generator
15:15
Obtaining a Voltage Source: Battery
16:19
Speed of Electricity
17:17
Speed of Electricity
17:18
Example 1: Electric Current & Moving Charge
19:40
Example 2: Electric Current & Resistance
20:31
Example 3: Resistivity & Resistance
21:56
Example 4: Light Bulb
25:16
Electric Circuits

52m 2s

Intro
0:00
Electric Circuits
0:51
Current, Voltage, and Circuit
0:52
Resistor
5:05
Definition of Resistor
5:06
Conceptual Example: Lamps
6:18
Other Fundamental Components
7:04
Circuit Diagrams
7:23
Introduction to Circuit Diagrams
7:24
Wire
7:42
Resistor
8:20
Battery
8:45
Power Supply
9:41
Switch
10:02
Wires: Bypass and Connect
10:53
A Special Not in General
12:04
Example: Simple vs. Complex Circuit Diagram
12:45
Kirchoff's Circuit Laws
15:32
Kirchoff's Circuit Law 1: Current Law
15:33
Kirchoff's Circuit Law 1: Visual Example
16:57
Kirchoff's Circuit Law 2: Voltage Law
17:16
Kirchoff's Circuit Law 2: Visual Example
19:23
Resistors in Series
21:48
Resistors in Series
21:49
Resistors in Parallel
23:33
Resistors in Parallel
23:34
Voltmeter and Ammeter
28:35
Voltmeter
28:36
Ammeter
30:05
Direct Current vs. Alternating Current
31:24
Direct Current vs. Alternating Current
31:25
Visual Example: Voltage Graphs
33:29
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 Switch
45:14
IX. Magnetism
Magnetism

25m 47s

Intro
0:00
Magnet
1:27
Magnet Has Two Poles
1:28
Magnetic Field
1:47
Always a Dipole, Never a Monopole
2:22
Always a Dipole, Never a Monopole
2:23
Magnetic Fields and Moving Charge
4:01
Magnetic Fields and Moving Charge
4:02
Magnets on an Atomic Level
4:45
Magnets on an Atomic Level
4:46
Evenly Distributed Motions
5:45
Unevenly Distributed Motions
6:22
Current and Magnetic Fields
9:42
Current Flow and Magnetic Field
9:43
Electromagnet
11:35
Electric Motor
13:11
Electric Motor
13:12
Generator
15:38
A Changing Magnetic Field Induces a Current
15:39
Example 1: What Kind of Magnetic Pole must the Earth's Geographic North Pole Be?
19:34
Example 2: Magnetic Field and Generator/Electric Motor
20:56
Example 3: Destroying the Magnetic Properties of a Permanent Magnet
23:08
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Lecture Comments (17)

1 answer

Last reply by: Professor Selhorst-Jones
Sat Jan 11, 2014 11:17 AM

Post by Jack Wilshere on January 11, 2014

Hello, I do not understand how the third example obeys the law of conservation of energy. Let's say the guy has a weight of 800 N and the height of the entire system is 3 m. At the top, the gravitational potential energy he has is 2400 J (800*3), yet the energy he spends going up is only 1200N (since the force that he exerts is only 1200 N and the distance traveled is 3m). What's going on?

1 answer

Last reply by: Professor Selhorst-Jones
Sun Jul 28, 2013 9:05 PM

Post by enya zh on July 27, 2013

How come the moon doesn't drop into the Earth? What does it mean to have the moon in freefall?
Thanks!!!☺

3 answers

Last reply by: Professor Selhorst-Jones
Fri May 24, 2013 2:08 PM

Post by Goutam Das on May 24, 2013

My questions may seem like unusual.Sorry about that.
1.I have no doubt about that the forces will be always equal, but the question is "why they are always equal"?
2.And What is the "source of that opposite force": Electromagnetic Force or something else?
3.Is there any "exception" of The 3rd Law?

1 answer

Last reply by: Professor Selhorst-Jones
Fri May 24, 2013 11:15 AM

Post by Goutam Das on May 24, 2013

Hi Professor,
In the third example, why does pulling upwards with a pulley yield twice the force?

6 answers

Last reply by: Professor Selhorst-Jones
Wed Nov 21, 2012 2:21 PM

Post by Tanveer Sehgal on November 20, 2012

Hey,

In the third example, there are two tensile forces acting in the positive direction and 1 in the negative direction. So why is it that we do not consider the force acting in the negative direction? The net force 2T-Fg. Why is not T-Fg?

Newton's Third Law

  • Forces always come in pairs: each force is equal in magnitude, but opposite in direction. Taken together, they would cancel each other out.
  • This is true of all forces.
  • If forces always come in pairs that can cancel each other out, why don't we normally see it come into play when we're working on problems? Two main reasons:
    • The force in the problem is external to the system. The force is guaranteed, and we don't care what happens to the thing causing the force.
    • The "equal and opposite" force is somehow translated into the Earth, where the planet's large mass makes it negligible.

Newton's Third Law

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Newton's Third Law 0:50
    • Newton's Third Law
  • Everyday Examples 1:24
    • Hammer Hitting a Nail
    • Swimming
    • Car Driving
    • Walking
  • Note 3:57
    • Newton's Third Law Sometimes Doesn't Come Into Play When Solving Problems: Reason 1
    • Newton's Third Law Sometimes Doesn't Come Into Play When Solving Problems: Reason 2
  • Example 1: What Force Does the Moon Pull on Earth? 7:04
  • Example 2: An Astronaut in Deep Space Throwing a Wrench 8:38
  • Example 3: A Woman Sitting in a Bosun's Chair that is Hanging from a Rope that Runs Over a Frictionless Pulley 12:51

Transcription: Newton's Third Law

Hi, welcome back to educator.com, today we are going to be talking about Newton's third law.0000

Put your hand, just as a quick experiment, on the edge of the table, or something hard that is fixed in place, and push for a while.0005

Just push for 10 seconds or so, and then take a look at what the bottom of your hand looks like.0014

If you look at it, you will notice that there is actually a mark on your hand, there will be some sort of line, or some sort of indentation.0020

So what happened?0030

You were pushing on the table, but what happened to your hand?0031

Your hand got pushed back on by the table.0034

Every force is going to have a force that resists it.0037

There is going to be an equal and opposite reactionary force.0040

If you push a certain amount of force into the table, the table is going to push a certain amount of force back into your hand.0042

You push on the table, it pushes back on you.0048

Newton's third law, one way to put it, (Newton put it in a slightly different way himself), but in modern language, 'Whenever an object a force on another object, the second object exerts a force of equal magnitude in the opposite direction, on the first object'.0052

If you put in a force of some amount of newtons, say, x N this way, the object is going to put a force of x N this way.0067

If you put it symbolically, the force of A on B = - the force of B on A, but negative, i.e. FA-B = - FB-A, so same magnitude, but opposite directions.0075

Just some basic everyday examples..0085

How about the hammer hitting a nail?0088

We have got a nail like this, and a hammer comes down on it, what happens?0090

The hammer hits the nail, and bounces back off, stops in place, the nail gets driven down into the wood, so there is definitely a force on the nail, but the hammer stops, for the hammer to stop, there has to be a force on the hammer.0099

The amount of that force is the amount of force that the hammer puts in to the nail, the same amount of force that the hammer gets from the nail.0112

They are going to be in opposite directions, but they are going to be equal, and that is what stops the hammer, and moves the nail, and then friction arrests the movement of the nail, we will talk about that later when we get to friction.0119

What if you are swimming?0129

If you are swimming, you are swimming along, you got yourself in the water, and you push on the water this way.0131

For example, if you do a breaststroke, and when you are swimming like this, your hands are cupping the water, they are catching the water, and they are pushing against the water.0140

So, you push against the water, and because you are pushing against the water, the water pushes back on you, which pushes you forward.0148

If you are driving along in a car, the car, it has wheels, (we have not talked about friction yet, we will very soon), the wheels, they push on the earth, they spin , and because of friction, them trying to rotate, pushes on the earth.0155

They are going to try to rotate this way, the wheels try to rotate this way, because of their friction, they have got friction, they stick to the earth, they are going to push the earth this way, the response of which is going to push the car this way.0178

Friction once again, combined with Newton's third law, is what gives our car motion.0189

When we walk on the earth, when you walk along, your foot pushes into the earth at a certain amount, which is going to cause you to be pushes in the opposite direction.0196

You push on the earth, if you want to jump, you bend your knees, and you push down really hard, and that is going to result in you getting pushed up, which is going to cause you to fly up into the air.0210

That is how you move, you move by pushing on something, and it responds because of Newton's third law, every force has an equal and opposite reaction force.0223

You push a certain amount , and that thing is going push back on you with that same amount in the opposite direction.0232

A careful thing to pay attention to is that, Newton's third law is always true, but often when we are working on our problems, it will not come into play.0239

It is still there, it is still happening, but this is because our problems are not normally going to have to include Newton's third law in the way we think about it.0247

It is still there if you want to think about it, but it will not have any effect on what we are doing in our work.0255

One reason why it often happens is that the force in the problem is external, it is guaranteed by the problem, we do not care what happens to the thing causing the force.0260

Very often we have talked about a block on a frictionless table or a block on a table.0269

We put some force into that block, what is putting that force in the block?0275

We do not know, it could be rockets on the back of the block, or it could be a person just standing there and pushing on the block, and so let us say it is a person standing there pushing on the block.0279

What happens to the person?0293

The person is going to wind up getting pushed back by the block by the amount that he push on the block.0294

But, we have been guaranteed by the problem, we have been told that a constant force is being applied, so we know that the person is somehow dealing with the force from the block, probably by putting it into the earth, by pushing against feet, and they are managing to handle the force that they are getting back from the block, and manage to keep up a constant force.0300

However the force is handled, we are guaranteed by the problem that there is a constant force, so with that point we can just deal with the constant force.0318

We do not have to worry about where the other part of it is going, because we have been given this external force that is guaranteed.0325

We do not have to care about where the forces are coming from, because it is given to us in the problem statement, it is given.0331

The other thing is, equal and opposite forces are often translated into the earth.0338

For example, with the person pushing on the block, which cause the person to be pushed back by a certain amount.0341

What does that person do?0354

The person then translates that force by pushing into the earth with his legs, which then cancels it out, so the amount that they get pushed by this becomes zero, because they get a net force of zero.0356

They put a push into the ground, (push by the person are in 'blue'), they push a blue up here, and a blue down here with their legs.0368

So the reactionary force is, from the person's point of view, they wind up experiencing the reaction forces, so the two cancel out, the person stands still, they can manage to keep up that constant force.0382

What happens to the force that gets us into the earth?0393

The equal and opposite force, if they get translated into the earth (or any planet), it is normally expected that the planet's mass is so large, so incredibly large compared to the force put into it, that it is going to experience this miniscule acceleration, we do not have even have to care about it, because the acceleration is so small, it is of little consequence.0396

Mass is giant for the earth, compared to these forces we are dealing with, they are comparatively puny, so there is no effect on the earth as far as we are concerned.0415

Let us start looking at some examples.0425

Let us say that the earth is sitting here, and up in the sky, we have got the moon.0427

If the earth exerts a pull of force of gravity Fg on the moon, how much does the moon pull on the earth?0436

So, Fg has been pulled by the earth.0448

We can turn these into vectors if we want, so, Fg is pulled by the earth on the moon, how much does the moon pull back on earth?0452

It is just going to be the equal and opposite force.0461

Gravity is a two way street, and so, - Fg is the exact amount that the moon is going to pull on earth, because it is going to pull with the exact same magnitude, but in the opposite the direction, they are pulling towards one another.0463

Why is the moon not falling to the earth?0481

We will talk about that later, when we talk about how gravitation works, the fact that moon is basically in continuous free fall, and the pull is what keeps it in that free fall as opposed to just slinging off into space, but we will talk about that in a future section.0483

For now, we have to understand the gravity is equal between the two things.0495

Same if you are sitting wherever you are, standing wherever you are, the earth is pulling on you, but you are also pulling on the earth by a certain amount.0500

From the earth's point of view, it is hardly going to notice you because your mass is so slow compared to the earth's mass.0508

But, you are still exerting a force on the earth, and it is equal to your own weight.0514

Second example: Say there is an astronaut in deep space, and he has got no external forces acting on him.0519

The astronaut has a wrench.0531

Now, what happens if the astronaut throws that wrench, the astronaut has a mass of 100 kg, and over here, we have got, mass of wrench = 2 kg .0536

The astronaut throws the wrench by applying a force of 50 N on the wrench.0552

He applies it for time = 0.2s.0562

What is the wrench's velocity?, what is the astronaut's velocity?0568

Normally when we would have talked about this being on earth, the person would have translated the force from the throw through their legs, and made it so that they had no force.0572

But this person is currently in deep space.0580

He has no where he can translate this force, so the throw is going to affect him equally.0581

So what is the force on the person?0586

From Newton's law, we know that they have to be equal and opposite, so the astronaut is going to also experience a 50 N force.0589

It is going to be going in the opposite direction.0595

So, what is the wrench's velocity?0598

We just use F = ma , 50 N = (2 kg) × a , a = 25 m/s/s, is the acceleration of the wrench.0600

What is the acceleration of the astronaut?0619

Fon the astronaut = maon the astronaut , - 50 = 100 × a (negative because it is in the opposite direction, and since we took the other as the positive direction), a = (1/2) m/s/s .0622

Once again, keep attention to where your units are, although we have been dropping them for ease.(it will save you from making a really simple foolish mistake.)0659

Now, if we want to know what the velocity is, well, how long do they experience the acceleration?0680

They experience the acceleration for 0.2 s, so velocity = a × t .0685

So, for the wrench, velocitywrench = 20 × 0.2 = 5.0 m/s.0694

What about for the astronaut?0710

Velocityastronaut = (-1/2)m/s/s × 0.2 s = -0.1 m/s.0713

So they are going to wind up experiencing very different velocities because of their very different masses, just like the experience between you and the earth, you notice the pull off the earth, but the earth hardly notices the pull of you, because of your very different masses.0732

It is the same thing with the astronaut and the wrench.0745

He will throw the wrench, and the wrench will move away from him 50 times faster than him moving in the opposite direction, because his mass is 50 times more. He currently weighs nothing, because he is in deep space.0747

But the inertia is going to be 50 times more.0760

So we have go the answer here, we know that it is going to move at 5 m/s, and the astronaut is going to move in the opposite direction at 0.1 m/s.0763

Third example: For this one, we have got a woman sitting in a bosun's chair, (bosun's chair is designed to help to make it easier for you to lift yourself up, used in sailing, used in window washing things like this).0772

It is hanging from a mass-less that runs over a mass-less frictionless pulley.0786

The chair and the woman have a combined mass of 75 kg.0789

With what force does she need to pull on the rope to have a constant velocity?0797

What force does she need to pull for it to have an acceleration of 1 m/s/s?0803

Let us think about what happens when she pulls.0808

She pulls down with some force, and that is going to be the force that becomes the tension.0810

So she pulls down with some T, now this force is translated into the rope, so we have got this pull coming along, and it is going to pull up here, with a force of T.0814

But, we have not paid attention to Newton's third law.0828

If you try to yank on something, if you are climbing, if you are pulling a rope, you put a tension into it, which cause you to rise, because the amount of tension that you put into the rope is the amount of force resultant o you, going in the opposite direction.0831

The resultant force from her pull is going to be T.0845

So, what is the total force that the woman is going to experience from the pull?0849

She is going to experience 2T going up.0852

What other forces are on her?0855

Her weight = Mg, and she has got a 2T going.0857

So, if she wants to have a constant velocity, we need the sum of the forces = mass × acceleration, if we want constant velocity, that is going to be equal to zero.0865

So (making up the positive direction), 2T - Mg = 0 (no acceleration).0874

So, 2T = Mg, T = 75 × 9.8 / 2 , T = 367.5 N, is the tension that she needs to put into the rope.0890

What if she wants to have an acceleration of 1 m/s/s?0911

Very similar, 2T - Mg = M × 1, T = (Mg + M)/2 , T = ((75 × 9.8) + 75) / 2 , T = 405 N .0916

Notice, she is able to do this at a very different rate, she is able to put way less force into pulling herself up using the bosun's chair because she is taking advantage of the Newton's third law.0952

She knows that by putting a tension into the rope, she is going to get lifted by that tension doubly, by the resultant force from pulling, the tension put into the rope will wind up pulling her up, but so will the resultant force.0960

She is making Newton's third law work for her, it is helping her out in this case.0980

So she is able to pull with considerably less than what her weight is.0984

She is going at a constant velocity, she only has to pull at half her weight.0987

So that is a really clever way to be able to use less effort on our part, to be able to go up.0991

We are able to take advantage of the way Physics works.0996

That is the end for Newton's third law.0999

Hope this made sense.1001

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