Discover Physics

Discover Physics

Benjamin Crowell
Published in: Light and Matter
Release Year: 2004
ISBN: 0-9704670-8-7
Pages: 212
Edition: First Edition
File Size: 12 MB
File Type: pdf
Language: English

Description of Discover Physics

Since birth, you’ve wanted to discover things. You started out by putting every available object in your mouth. Later you began asking the grownups all those “why” questions. None of this makes you unique — humans are naturally curious animals. What’s unusual is that you’ve decided to take a physics course. There are easier ways to satisfy a science requirement, so evidently you’re one of those uncommon people who has retained the habit of curiosity into adulthood, and you’re willing to tackle a subject that requires sustained intellectual effort. Bravo! A reward of curiosity is that as you learn more, things get simpler.
“Mommy, why do you have to go to work?” “Daddy, why do you need keys to make the cargo?” “Grandma, why can’t I have that toy?” Eventually, you learned that questions like these, which as a child you thought to be unrelated, were actually closely connected: they all had to do with capitalism and property. As a scientific example, William Jones announced in 1786 the discovery that many languages previously thought to be unrelated were actually connected. Jones realized, for example, that there was a relationship between the words “bhratar,” “phrater,” “frater,” and “brother,” which mean the same thing in Sanskrit, Greek, Latin, and English. 
Many apparently unrelated languages of Europe and India could thus be brought under the same roof and understood in a simple way. For an even more dramatic example, imagine trying to learn chemistry hundreds of years ago, before anyone had discovered the periodic table or even the existence of atoms. Chemistry has gotten a lot simpler since then! 
Sometimes the subject gets simpler, but it takes a while for the textbooks 'Discover Physics' to catch up. For hundreds of years after Hindu mathematicians incorporated negative numbers into algebra, European texts still avoided them, which meant that students had to endure a lot of confusing mumbo jumbo when it came to solving an equation like x + 7 = 0. Physics has been getting simpler, but most physics books still haven’t caught up. (Can you detect the sales pitch here?) The newer, simpler way of understanding physics involves symmetry.

Content of Discover Physics

1 The Rules of the Rules 

1.1 Symmetry
1.2 A Preview of Noether’s Theorem.
1.3 What Are The Symmetries?
Lab 1a: Scaling.

2 The Ray Model of Light 21

2.1 Rays Don’t Rust
2.2 Time-Reversal Symmetry
2.3 Applications
The inverse-square law, 24.—Parallax, 25.
2.4 The Speed of Light
The principle of inertia, 28.—Measuring
the speed of light,
2.5 Reflection
Seeing by reflection, 30.—Specular
reflection, 30.
Lab 2a: Time-Reversal and Reflection
Lab 2b: Models of Light
Lab 2c: The Speed of Light in Matter

3 Images 45

3.1 Location and Magnification
A flat mirror, 46.—A curved mirror,
3.2 Real and Virtual Images
3.3 Angular Magnification
Lab 3a: Images
Lab 3b: A Real Image
Lab 3c: Lenses
Lab 3d: The Telescope

4 Conservation of Mass and Energy 61

4.1 Conservation of Mass 
4.2 Conservation of Energy 
Kinetic energy, 63.—Gravitational energy,
64.—Emission and absorption of light,
66.—How many forms of energy
4.3 Newton’s Law of Gravity 
4.4 Noether’s Theorem for Energy.
4.5 Equivalence of Mass and Energy.
Mass-energy, 74.—The correspondence
Lab 4a: Conservation Laws.
Lab 4b: Conservation of Energy 

5 Conservation of Momentum 89

5.1 Translation Symmetry 
5.2 The Strong Principle of Inertia
Symmetry and inertia, 91.—Inertial and
noninertial frames, 93.
5.3 Momentum.
Conservation of momentum, 96.—

Momentum compared to kinetic energy,

100.—Force, 101.—Motion in two
dimensions, 103.
Lab 5a: Interactions 
Lab 5b: Frames of Reference
Lab 5c: Conservation of Momentum 
Lab 5d: Conservation of Angular Momentum

6 Relativity 121

6.1 The Principle of Relativity
6.2 Distortion of Time and Space 
Time, 125.—Space, 126.—No simultaneity,
126.—Applications, 128.
6.3 Dynamics
Combination of velocities, 133.—
Momentum, 134.—Equivalence of mass
and energy, 137.

7 Electricity and Magnetism 143

7.1 Electrical Interactions
Newton’s quest, 144.—Charge and electric
field, 145.
7.2 Circuits 
Current, 149.—Circuits, 151.—Voltage,
152.—Resistance, 153.—Applications,
7.3 Electromagnetism 
Magnetic interactions, Relativity re-
quires magnetism, Magnetic fields,
7.4 Induction.
Electromagnetic signals, 166.—Induction,
169.—Electromagnetic waves,
7.5 What’s Left?
Lab 7a: Charge. 
Lab 7b: Electrical Measurements 
Lab 7c: Is Charge Conserved?
Lab 7d: Circuits
Lab 7e: Electric Fields
Lab 7f: Magnetic Fields
Lab 7g: Induction
Lab 7h: Light Waves 
Lab 7i: Electron Waves 

Appendix 1: Photo Credits 207
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