Physics 10 Reviewer.docx

**Lesson 1 - [Initial Remarks on Science and Physics](https://uvle.upd.edu.ph/course/view.php?id=19168#section-2)** **Visitors From Twilo** - Taken from Leon Lederman's "The God Particle" - Imagine an intelligent race of beings from the planet Twilo. - They look more or less like us, they...

**Lesson 1 - [Initial Remarks on Science and Physics](https://uvle.upd.edu.ph/course/view.php?id=19168#section-2)** **Visitors From Twilo** - Taken from Leon Lederman's "The God Particle" - Imagine an intelligent race of beings from the planet Twilo. - They look more or less like us, they talk like us, they do everything like humans - except for one thing, they can't see objects with a sharp juxtaposition of black and white - A contingent from Twilo comes to Earth on a goodwill mission - We take them to see one of the most popular cultural events on the planet: **Twiloans Try to Make Sense of Soccer** - Young Pipsqueak Twiloan: "Let\'s postulate the existence of an invisible ball." - Elders: Say what? - How did the pipsqueak come up with the idea? **Planet Neptune's existence was predicted by** **Urbain Le Verrier this way!** **Diagnostic Features of Science** - **Repeatability** - The same phenomenon is sought again and again, preferably by independent investigation, and the interpretation given to it is confirmed or discarded by means of novel analysis and experimentation**.** - **Economy** - Scientists attempt to abstract the information into the form that is both simplest and most pleasing - the combination called elegance - while yielding the largest amount of information with the least amount of effort - Occam's Razor: The simplest explanation is usually the best - **Mensuration** - If something can be properly measured using universally accepted scales, generalizations about it are rendered unambiguous - Consider process of observation with human senses, it really creates a mental model of the real world, as macroscopic approximation to the microscopically comprised real world. Therefore absolute reliance on perceived fact are subject to error induced by crudeness of model - **Heuristics** - The best science stimulates further discovery, often in unpredictable new directions, and the new knowledge provides an additional test of the original principles that led to the discovery - **Consilience** - The explanations of physical phenomena most likely to survive are those that can be connected and proved consistent with one another **Skill Sets** Perspective/Open-mindedness - Science is thinking beyond, out of, and of the "box" - Example: Heliocentrism VS Geocentrism Sense Making - Science is not just accumulating facts but putting them together in a coherent way - Example: existence of atoms Ability to Falsify - Karl Popper: "It is easy to obtain confirmations, or verifications, for nearly every theory --- if we look for confirmations. - "Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability\..." - Example: Phlogiston theory **PHYSICS** - From the Greek word "phusis" (sometimes "physis") which means nature - Physics is difficult to define since the subject has been evolving - Instead of trying to define physics, we attempt to characterize it instead Characterizing Physics - Goals -- To understand nature, that is, rationalize, explain and predict physical phenomena - Strategy -- Use of abstraction or unifying concepts (e.g. energy, entropy, charge, force, etc.) - Tools -- Mathematical models, experiments, computational work - Subfields -- Up to the 19th Century: Astronomy, Mechanics, Acoustics, Fluid Mechanics, Electromagnetism, Optics, Thermodynamics, Statistical Physics -- Modern Physics: Relativity, Cosmology, Astrophysics, Quantum Mechanics, High Energy Physics, Condensed Matter Physics, Chaos, Nonlinear Dynamics, Complex Systems, Biological Physics, Earth Systems Physics - Physics is about Frontiers! -- Dark Matter, M-Theory, Quantum Computing, etc. **7 Important Ideas in Physics** 1. The Earth is not the center of the universe (**Copernican Astronomy**) 2. The universe is a mechanism run by rules (**Newtonian Mechanics And Causality**) 3. Energy is what makes it go (**The Concept Of Energy**) 4. Entropy tells it where to go (**Entropy And Probability**) 5. The facts are relative but the law is absolute (**Relativity**) 6. You can't predict or know everything (**Quantum Theory And The End Of Causality**) 7. Fundamentally, things never change (**Conservation Principles And Symmetry**) Lesson 2 - [**The Greeks and The Homocentric Model**](https://uvle.upd.edu.ph/course/view.php?id=19168#section-3) **Greeks, Matter, Motion, and the Universe** **Natural Philosophy and the Role of Mathematics** **Greece 7th Century B.C.** - The Universe is a rational place, with natural laws that can be figured out. **Natural Philosophy** - An attempt to develop a consistent set of "natural laws" to explain physical phenomena without reference to supernatural causes / beings. Pythagoras - 1 -- represented reason, for reason could produce only one consistent body of truth - 2 -- stood for man - 3 -- stood for woman - 4 -- symbol for justice, being the first number that is the product of two equals - 5 -- identified with marriage, because it is formed by the union of 2 and 3 A diagram of different types of motion Description automatically generated Greeks guided by a paradigm first articulated by Pythagoras (c569\--475 B.C.E) before Socrates\' time. Key points about the movements of celestial objects: 1. The planets, Sun, Moon and stars move in perfectly circular orbits. 2. The speed of the planets, Sun, Moon and stars in their circular orbits is perfectly uniform. 3. The Earth is at the exact center of the motion of the celestial bodies. **Some Things that the Greeks Got Right** 1. Diurnal and Annual Motion 2. Hipparchus: precession of the equinoxes, systematic recording of observational astronomy 3. Earth is spherical 4. Eratosthenes: Good estimate for the size of the Earth 5. Time between 1st Quarter and Last Quarter not the same as time between Last Quarter and 1st Quarter 6. Retrograde Motion **How do we reconcile the Pythagorean paradigm with the observed motion of the heavenly bodies ?** **Plato: "Allegory of the Cave"**  **Plato: "Saving the Appearances"** - Observed motion = combinations of uniform circular motion - Task for future Philosophers: Explain the observed motion of the heavenly bodies in terms of combinations of uniform circular motions. **Greek View of the Universe** - Geocentric theory of the universe "Earth-centered universe" - Early Greek Universe : Earth + celestial spheres (Eudoxus, Aristotle) A diagram of the solar system Description automatically generated **Eudoxus (Homocentric Model)** - **Moon:1+2** - **Sun:1+2** - **Venus:1+3** - **Mercury:1+3** - **Mars :1+3** - **Jupiter:1+3** - **Saturn:1+3** - **Stars: 1** - **TOTAL: 27 SPHERES** **Aristotle's Model** - Problem with Eudoxus: "Intelligences" etc. - Introduced: Prime Mover + 28 other spheres (gear-like mechanism) **Problems with Aristotle's Model** Can't Explain: - Change in apparent size of moon - Change in brightness of the planets **Greek View of the Universe** - Geocentric theory of the universe "Earth-centered universe" - Early Greek Universe: Earth + celestial spheres (Eudoxus, Aristotle) - Ptolemy's Universe: Additional devices to account for actual observations. \[Details next meeting\] **Minority View:** Aristarchus (310-230 B.C., Greek) - the Sun is in the center of the universe - theory considered too radical - note that he was 1,750 years ahead of Copernicus Quiz: In the Pythagorean system of numbers, 5 stood for marriage. Using a single word, what do you think the number 6 stood for? Briefly explain why. In the Pythagorean system, the number **6** stood for \"**harmony**.\" This is because 6 is considered a \"perfect number\" in mathematics, being the sum of its divisors (1, 2, and 3), and symbolizes balance and proportion. In Pythagorean philosophy, harmony reflected balance in life and the cosmos. Lesson 3 - [**The Fall of Geocentric Theory and The Rise of Heliocentric Theory**](https://uvle.upd.edu.ph/course/view.php?id=19168#section-4) **Ptolemy'Geocentric Model** **Ptolemy's Calculational Devices** - Deferent - Epicycle - Eccentric - Equant   As a planet moves around on its epicycle, the center of the epicycle (called the "deferent\'\') moves around the Earth. When its motion brings it inside the deferent circle, the planet undergoes retrograde motion. **COPERNICUS and the Heliocentric Model of the Universe**  COPERNICAN MODEL **version 1 vs. version 2** A diagram of a circle with a point and a circle with a point and a circle with a point and a circle with a point and a circle with a point and a circle with a point and Description automatically generated **Theological / Philosophical Grounds Against the Model** - The Earth should be different from other planets since it should be in a special place in the universe (Giordano Bruno's "heresies"). - Other planets will not be perfect - Other "earthly beings" must exist - Heliocentric model would lead to Sun worship. **Physical Grounds Against the Model** 1. Stellar parallax is not observed since constellations do not disarrange.  2. Apparent size of stars does not change 3. Violated expectations of the Aristotelian physics prevalent in his time: a. Breeze at thousands of miles per hour b. Falling motion should not be simpler c. Spinning earth would fly apart d. Unimaginable amount of force would be required to keep Earth moving **Apologetic Response for Copernican Model** - Useful for calculations - Not necessarily connected with reality A close up of a book Description automatically generated **Increased support for research** Impressed by Tycho's observation in 1572, construction of research facilities was financed by King Frederick II (Denmark and Norway) and later emperor Rudolf II (Roman Empire). **Tycho Brahe (1546 - 1601)** - Greatest naked-eye astronomer - Proved that comets were celestial objects - Proved that a supernova was a celestial object **Significant Contributions of Tycho Brahe** 1. Discovery of a "nova stella" -- Not due to earth's atmosphere (no parallax) -- Stars are not eternal 2. Accurate astronomical data for his time -- Stellar and planetary positions -- Better measure of earth's axial tilt -- Anomalies in Ptolemaic model surfaced 3. Proved that comets are celestial objects 4. Removed the necessity of crystalline celestial spheres **TYCHONIC MODEL** Tychonic system appeals to both the homocentric principle and the heliocentric revolution of other planets. - Strange hybrid of geocentrism and heliocentrism - Earth was at center - Sun orbits earth - Planets orbit sun **Laws Of Planetary Motion** - Brahe died without having confirmed the validity of his model. - Kepler inherited vast amount of data. Trial And Error Fits Lead to Laws Of Planetary Motion - Copernican and Tychonic models do not fit. - Introduced new heliocentric models but none fitted. - It took 20 years to eventually end up with an empirical model... **Kepler's Three Laws of Planetary Motion** 1. Law of orbit. Planets orbit the sun in elliptical orbits with the sun at one of the focii. 2. Law of equal areas. The line joining a planet, and the sun sweeps equal areas at equal times. 3. Law of period. The square of the period of a planet's revolution is directly proportional to the cube of its average distance from the sun. **Erasing Theological Doubts**  **Galileo Galilei (1564-1641)** - Improved early telescope designs - Made many observations of heavenly bodies. **Galileo's Astronomical Observations** - Craters of the moon - Sunspots - Saturn's rings - Moons of Jupiter - Phases of Venus - Unchanging size of stars (indication of their vast distance) \` **Ptolemy's Model Cannot Explain** **Copernican Model's Elegant Explanation** --------------------------------------- -------------------------------------------- Venus is always between earth and sun Venus can travel behind the sun **Publication of Arguments** - Dialogue Concerning the Two Chief World Systems (Dialogo) - Conviction of "grave suspicion of heresy" - Disguised as "Dialogue on the Tides" - Characters: - Salviati -- Copernican position (name of friend) - Sagredo -- intelligent layman, neutral (name of friend) - Simplicio -- Ptolemy and Aristotle's position Discourse lasted four days **Needed final touch up of the model** - Kepler's laws are empirical laws: model is fitted to the data. - Needs a physical theory that supports the current model. **QUIZ** Briefly explain how the Aristotelian/Eudoxan, Ptolemaic, and Copernican explanations of retrograde motion differ. **Ans.** The Aristotelian/Eudoxan model explained retrograde motion with complex spheres around Earth. The Ptolemaic model used small circular orbits (epicycles) to make planets appear to move backward. The Copernican model, which placed the Sun at the center, explained retrograde as an illusion when Earth overtakes a slower-moving planet. Lesson 4 - [**Aristotelian Physics and Galilean Mechanics**](https://uvle.upd.edu.ph/course/view.php?id=19168#section-5) **Aristotle & Greek Thought** - Aristotle's scientific system influenced medieval Christian and Islamic thought until the late 17th century. - Despite later intellectual revolutions, Aristotelian ideas stayed rooted in Western thought. - His work was the first to describe the physical universe using logical arguments based on basic assumptions. - Aristotelian ideas dominated for 2000 years. **Aristotelian Physics** - **Types of motion** - Celestial - Alteration - Natural - Violent - **Aristotle and the Four Elements** - Fire - Wind - Water - Earth **Violent Motion** - Motion caused by an external force - Once an arrow is released, how does it keep on moving? - Antiperistasis! **Aristotle's Laws of Motion** - First Law - The speed of falling is proportional to the weight of the object. Heavier things fall faster. - Second Law - The speed by which an object falls depends inversely on the density of the medium it is falling through. - Additional Notes: In violent motion, the speed of the object is proportional to the applied force Aristotle asserted that during violent motion the speed of the object is directly proportional to the applied force. **Why did Aristotelian Physics prevail?** - The power of theory and abstraction - Manual work is not for free citizens - Experiment was not easy to conduct in ancient times **Galileo vs. Aristotle** **Aristotle**: **LOGIC** is the best test of knowledge **Galileo**: **EXPERIMENT** is the best test of knowledge Motion according to Aristotle - Falling Motion - Object's fall at a rate proportional to their weight - Heavy objects fall faster than light objects - Falling motion is uniform motion (constant speed). - Horizontal Motion - An impetus is required to sustain motion. - Projectile Motion - Two mechanisms for projectile motion Motion according to Galileo - Falling Motion - Falling is independent of weight. - Falling is uniformly accelerated. - Horizontal Motion - To sustain motion, no force is needed - Force is only required to change motion, not sustain it. - Projectile Motion - Projectile motion is a superposition of vertical and horizontal motion Status of Heliocentric vs. Geocentric Debate after Galileo's Studies in Mechanics - Aristotelian Physics is wrong - Galileo: Horizontal motion = circular motion Additional notes on Galileo - Galileo was often right but was sometimes wrong e.g. - Ignored Kepler and his elliptical orbits - Insisted on circular motion - Wrong explanation of tides **Status of Heliocentric vs. Geocentric Debate after Galileo, Brahe & Kepler's contributions (\~ca 1609- 1619)** - Ptolemaic Model abandoned - Tychonic vs. Copernican - Objections based on Aristotelian physics not yet addressed by Copernican Model - Kepler's 1st and 2nd Laws of planetary motion (1609) - Kepler's 3rd Law of planetary motion (1619) **Our Model of the Universe (ca 1642)** Better data Tycho Brahe ----------------------------- ----------------- Final touch-up of the model Johannes Kepler Promotion of the new mode Galileo Galilei **Still missing someone to put the pieces together to form a coherent physical theory in the modern sense** **Quiz** Using Aristotelian physics, briefly explain why a sheet of paper riddled with holes falls faster than a sheet of paper without holes **Ans**. In Aristotelian physics, objects fall based on their nature and interaction with the medium (air). A sheet of paper with holes has less resistance from the air because the holes allow air to pass through more easily. As a result, it encounters less opposition and falls faster than a solid sheet, which has more surface area for the air to push against. Lesson 5 - [**Newtonian Physics and the 3 Laws of Motion**](https://uvle.upd.edu.ph/course/view.php?id=19168#section-6) **Sir Isaac Newton** - Formulated the laws of motion based on experimental observations - "Qui genus humanum ingenio superavit" **Terminologies** - Vector -- a quantity with magnitude and direction - Force -- In a simplest sense, a push or a pull. Its source may be gravitational, electrical, magnetic or simply muscular effort \[measured in NEWTONS\] - Net Force -- a (vectorial) sum of all forces - Velocity -- rate of change of position, plus a direction - Acceleration -- rate of change of velocity **Free-Body Diagrams** - Used to show the relative magnitude and direction of all forces acting on the body in a given situation - Decide which body you are referring to - Draw only forces acting on the body **Newton's First Law -- \[Law of Inertia\]** - A body at rest w/ zero net force remains at rest - A body in motion keeps moving if there is zero net force acting on it - "A body acted on by no net force moves with constant velocity (which may be zero) and zero acceleration." **Ex. Ketchup bottle, trains, shaking wet hand, etc.** "The vis insita, or innate force of matter, is a power of resisting, by which every body, as much as in it lies, continues in its present state, whether it be of rest, or of moving uniformly forwards in a right line." "A body, from its inert nature of matter, is not without difficulty put out of its state of motion. Upon which account, this vis insita may, by a most significant name, be called inertia (vis inertiae) or force of inactivity." What happens when we push an object? - The more force....The more acceleration - The bigger the object, the lesser it accelerates. - It moves in the direction of the force. **Newton's 2nd Law -- Law of Acceleration** - "If a net external force acts on a body, the body accelerates. The direction of acceleration is the same as the direction of the net force. The mass of the body times the acceleration equals the net force vector." - [*F* = *ma*]{.math.inline} - A non-zero net force causes acceleration Mass Versus Weight - Mass -- The quantity of matter in an object. It is also the measure of inertia or sluggishness that an object exhibits in response to any effort made to start it, stop it, or change its state of motion in any way - Weight -- The force upon an object due to gravity Free Fall - near earth's surface - only gravity is acting - includes objects thrown upwards - constant acceleration with magnitude g = 9.8 m/s2 Uniform Circular Motion - Keeps on changing direction -\> must be accelerating! - The force causing the acceleration is known as the centripetal force - Inside the can, a bug feels the centripetal force as well (can pushes on her feet) - From the point of view of the bug, she is at rest, hence, the centripetal force must be countered by a centrifugal force **Observation leading to 3rd Law** - When the hammer exerts a force on the stake, it is brought to a halt in the process **Newton's 3rd Law - Action & Reaction** - "If body A exerts a force on body B (an "action"), then body B exerts a force on body A (a "reaction"). These two forces have the same magnitude but are opposite in direction. These two forces act on different bodies." - Action-reaction pair acts on different bodies. - This is why punching the floor hurts your hand, and why people wear gloves in boxing. - Earth acts on falling objects (this force being the weight of the object) at the same time, the object pulls on Earth with exactly the same magnitude **3rd Law in Action!** - Cannon and Cannonball - Bug versus Windshield Lesson 6 - [**Universal Law of Gravitation & Newtonian Synthesis**](https://uvle.upd.edu.ph/course/view.php?id=19168#section-7) **Center of Mass (Center of Gravity)** - Average position of all the mass that makes up the body - Center of mass obeys Newton's laws **Locating the Center of Mass** - Center of mass can be outside the body! **Stability & Tipping** - Stability is determined by the vertical distance the center of mass is raised in tipping - An object with a wide base and a low center of mass is more stable **Moon and It's Orbit** The tangential velocity of the moon about the earth allows it to fall around the earth rather than directly into it **Law of Gravitation** "Every particle of matter in the universe attracts every other particle with a force directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them." \ [\$\$F\_{g} = \\frac{Gm\_{1}m\_{2}}{r\^{2}}\\ \$\$]{.math.display}\ G = 6.67 x 10-11 Nm2/kg2 (Gravitational Constant) A close-up of a person Description automatically generated **Universal Gravitational Constant G** - Just as π relates circumference and diameter for circles, G relates force with mass and distance - First obtained by Henri Cavendish **Ocean Tides** - Caused by the differences in the gravitational pull between the moon and the earth on opposite sides of the earth - The sun gravitational pull on the earth is 180 times that of the moon. Why doesn't the sun cause 180 times greater than lunar tides? **Spring Tide vs. Neap Tide** - Spring Tide -- higher-than-average high tides and lower-than-average low tides - Neap Tide -- lower-than-average high tide and higher-than-average low tide **Gravity & the Model of the Solar System** - Why is the sun the center of the solar system? **Planetary Motions and The Center of Mass** Diagram of a diagram of a planet Description automatically generated **Newtonian Synthesis** During the time of Aristotle, bodies on earth are one of 4 elements while bodies on heaven are made of the 5th element known as the "quintessence". Due to the Newtonian synthesis, we learned that the motion of bodies in heaven obeys the same laws of motion as do bodies on earth. **Quiz** A person balances a meterstick on a horizontal position on the extended index finger of both hands. That person slowly brings the two fingers together. The stick remains balanced and the two fingers ALWAYS meet at the 50-cm mark (which in this case is the center of mass of the meterstick) regardless of their original positions. Explain this mind-blowing phenomenon using everything you know. Ans. The fingers meet at the center because of unequal friction. The finger with less weight slides first, while the one with more weight stays put due to higher friction. As this process alternates, both fingers eventually meet at the center of mass, where the stick is perfectly balanced.