PHY Notes

Chapter 1

Shared Sources of Knowledge
Authority: an accepted source of expert information or advice- trusting knowledge told to you
Intuition:the act or facility of knowing or sensing without the use of rational processes: not using regular 5 senses but have a hunch
Reason: capacity for logical, rational, and analytic thought- mathematics
Sensory data: knowledge obtained through senses- almost always trusted as truth
The Scientific MethodHypothesis: phenomenon or problem that can be tested
Theory: statement or principles devised to explain a group of facts or phenomena, especially that has been repeatedly tested and is widely accepted- theory of evolution
Law: a well-tested theory, so firm as to be unquestioned by science- law of gravity
Model: a schematic description of a system that can be used to father the study of its characteristics- model of an atom
Six “self-evident truths”1. Existence: a physical world separate and distinct form our minds- the chin’s man dream of being a butterfly (we are not living in a dream, but truly exist)
Actual watch
2. Causality: events in the world have a physical cause that can be explained- cause must always precede the effect (time traveler can “cause” death of parents)
Wheels that turn the hands
3. Position Symmetry: the laws of nature are the same everywhere in the universe- law of gravity works on African contienent, SF, and one galixy over
The second hand and the minute had tick constantly
4. Time Symmetry: the laws of nature have remained the same throughout time- Nuton’s laws are the same today
The time did not wear out throughout the entire day (seconds are the same am and pm)
5. Principle of Noncontradiction: Of two contradictory propositions, both cannot be true- theory of evolution or creationists (one truth assumption)
Either a little man lives in the clock and turns the wheels or the watch has a wheels that turn
6. Occam’s Razor: alternative explanation with the simplest explanation is chosen if it contains a completer explanation- theory that the sun revolved around the earth changed when the sensory data was discovered and the simple solar system was accepted
Not a little man living in the watch, but the small wheels turn the watch timer
The Universe Around Us
Interactions and ForceInteraction: (give rise to forces) any of the four (strong nuclear interaction, electromagnetic interaction, weak nuclear interaction, and gravity) ways in which elementary particles and bodies can influence each other
Force: a push or pull on an object. Felt by matter in accordance with attributes possessed by the matter
Four interactions in nature
1. Strong Nuclear Interaction: the interaction between nucleons that gives rise to the strong force (act on nucleons and quarks) most powerful force known but has a range so small that electromagnetic force dominates by the time we have increase the scale to the size of an atom- acts on quarks, binding them together into nucleons and also binding the nucleons together into atomic nuclei (nuclei do not fly apart only because the strong nuclear force is stronger than the electromagnetic)
2. Electromagnetic Interaction: the interaction between charged objects that gives rise to the electromagnetic force (act on charged particles) force that dominates the world in which we live- present in the nuclei as a repulsion between positively charged protons
3. Weak Nuclear Interaction: the interaction between nucleons that gives rise to the weak force
(act on nucleons and quarks) range so small that electromagnetic force dominates by the time we have increase the scale to the size of an atom- the only force that does not dominate at any scale- attempts to break nuclei apart
4. Gravity the interaction between anything with mass that gives rise the gravitational force (act on mass) increases slowly and steadily with increasing mass and becomes the dominant force when sizes we are considering are as large as planets or larger. As molecular assemblies increase in mass, the are eventaully held together by gravity instead of electromagnetism. Since gravity always pulls matter inward toward the center of the distribution, objects held together by gravity tend to have a round shape. For example earth is in the shape of a ball.
Force strength varies with distance. The relative strength listed here is what is felt by 2 protons sitting side-by-side (approximately 10 ^-15 m apart).
Force
Relative Strength
Range
Acts Upon

Nuclear Strong
10 ^38
Atomic Nuclei 10 ^ -15m
Nucleons

Electromagnetic
10 ^36
Earth Diameter 10 ^7m
Charged Matter

Nuclear Weak
10 ^25
Atomic Nuclei 10 ^-15m
Nucleons

Gravity
1
Entire universe 10 ^26m
Mass

　
Nuclear Interactions: The strong and weak forces
Atomic Nuclei: the positively charge central region on an atom (contains protons and neutrons or simply the nucleons)
Proton(nucleon): strongly interacting particle made up of three quarks (carry a positive electrical charge) in the nucleus of an atom and bound together by the strong nuclear force
Neutron (nucleon): composite, strongly-interacting particle made up of three quarks (carries no electrical charge) part of nucleus of atom and bound together by the strong nuclear force
Nucleon: generic name for either proton or neutron- so small that it would take on trillion lined up next to each other to reach across the head of a pin, but they are so dense that a pinhead-size ball made of nucleons packed next to each other would weigh about a million tons
Quark: elementary particles of which protons and neutrons consist (each nucleon contains 3) strong nuclear force acts on quarks and binds them together within the nucleons
Radioactive: term for nuclei that are susceptible to being changed or broken apart when under the influence of the various forces; rather than staying together from the strength of the strong nuclear force
The Electromagnetic Interaction
Electrons: elementary particle in atom (negatively charged) located outside of atomic nuclei. The average distance of the outermost electron from the nucleus is 100,000 times larger than its nucleus and most of that is simply empty space (if a nucleus were the size of a ballpoint pen tip, its surrounding atom would be the size of a football field)
Atom: fundamental unit of an element (nuclei and electrons bound together)
Elements: substance composed of atoms that have an identical number of protons in each nucleus and can be reduced to simpler substances by normal chemical means (nearly 100 natural elements on periodic table)
Molecules: atoms joined together, usually made up of more than one atom- table sugar molecule contains 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms
The Realm of the Gravitational Interaction
Solar System: the sun and all planets, comets, asteroids, and other bodies that orbit about it under the pull of gravity. (If the sun were an orange on the 50-yard line of a football field earth would be a BB 10 yards away and Neptune would be a marble 300 yards away on this scale all the material in the entire solar system combined would form a ball smaller than a grapefruit- most of space is empty space)


Chapter 2
Aristotle(1642-1727): concept of force being necessary to sustain all motion was thought to be true for nearly 2,000 years
Galileo Galilei: understood the law of inertia several decades before Isaac Newton
The first law of motion
Every object at rest, or in uniform motion, will remain in the state of uniform motion unless compelled to do otherwise by forces acting upon it- pulling a table cloth and seeing the dishes move (a car moving on ice does not have friction and therefore can move forward, and when the car turns a corner the passenger “slides” to the side but in reality the passenger is still moving forward due the first law of motion and is compelled to move sideways with the car )
Uniform Motion (uncelebrated motion): motion at a constant speed in a straight line
State of Uniform Motion: condition of an object when no unbalanced force acts upon it. A state of motion always refers to being at rest or in uniform motion.
Force: a push or pull on an object
Velocity and Acceleration
Velocity: the state of motion of an object; the distance in a paricular direction covered in a certain time and is mearused in miles per hour or meters per second (speed combined with the direction of the motion) use of arrow to show direction
Acceleration: (caused by force) rate of change of velocity per unit time; the rate at which speed or direction changes and measured in miles per hour per second or meters per second per second (change of velocity divided by the time required for the change)use of arrow to show direction
Force: Interduction to the second Law of Motion
Force: is that it is a push or a pull, exerted by one object on another with direction and several forces can act on one object. force is measured in punds or newtons
Net Force: the total force acting on an object; two people pushing one cart in the same direction increase the net force while two people pushing one cart in oposite directions decreases net force.
unbalanced forces: portion of the total force that is unopposed by other forces and so will cause an acceleration; the net force is NOT zero. This happens when ever an object moves faster, slower, changes direction, or experiences any combination of speed and directional changes.
Centraipetal acceleration: toward a center (air-hockey puck slides in a circle when acceleration is sideways and velocity is forward)
Mass
Mass: the characteristic of a body which determines how much it accelerates when a force is applied; a LARGER truck and a SMALLER car is a measure of mass
Weight: meausre of the force of gravity pulling on an object; changes with location
The Second Law of Motion
Force= mass x acceleartion or F=ma sometime written a=f/m
ex: an object that has a mass of 100 kilograms is pushed by a force that causes it to accelerate at a rate of 5 meters per second every second translates to 500 newtons=100 kilograms x 5 meters per second every second
THE THIRD LAW OF MOTION
3rd law of motion: forces occure only when 2 things interact with each other (car can accelearte only if its wheels touch teh road and push against it- interaction between the tires and pavement) All forces result from interactions between pairs of objects, each object exerting a force on the other. The two resulting forces have the same strength and act in exactly opposite directions.
equation: force of you on Earth= force of earth on you combined with the 2nd law it is stated earth's mas x earth's acceleration = your mass x your acceleartion, the earth is 10^23 times bigger than me and so the force is 10^23 times less than mine (an amount too small to measure) but assume I slip on a banana peel on my way to class the equatio becomes: force of you on teh banana peel = force of the banana peel on you or banana peel's mass x banana peel's acceleration = your mass x your acceleration, this time the banana peel has 1/1000 of my mass and the acceleration backwards must be 1000 times more than mine forward to balance the equation- meaning I fall over.

Chapter 3
Falling Objects the spped increase at a set rate (baseball off a clif fell for the first second 9.8m/sec, at the second 19.6m/sec, at the third 29.4m/sec, so on
tossed object: the amount of acceleration is the same as before but first second the ball's speed is 35-9.8=15.4m/sec, the second the ball's speed is 25.2-9.8=15.4m/sec; the thritd the ball's speed is 5.6m/sec, and just after 4 seconds in the air its direction changed and the speed is now 5.6-9.8=4.2m/sec downward
Uniform Acceleration
g: the symbol representing the acceleration caused by gravity. it is equal to 22 mi/hour per second or 32 ft/second per second or 9.8m/second per second depending on the units.
acceleration: The acceleration caused by gravity is constant regardless of the direction of the motion (up/down/sideways) the rate a cannonball slows while traveling upwards is teh same rate ait speeds up when coming down; objects all fall at teh same rate of acceleration regardless of their weight (ignoring the resistance from air)
Weight and Acceleration
weight: the force of gravity on an object; w=mg or weight=mass x acceleration caused by gravity (if the mass of 1 object is 2x the mass of another its weight is exactly twice as great)
the weight does not affect the acceleration of objects, but the force on the boulder has to be greater than the force on the rock to equal the acceleration. F=ma
CIRCULAR MOTION AND THE MOON'S ORBIT
1. the force of Earth's gravity on the Moon is essentially perpendicular to the Moon's velocity. Newton's idea to fire a large cannon off a huge, massive, really tall mountain that would have enough hight that it would send the cannon ball around the earth, because unlike a shorter cannon fire it would never hit the surface of the earth, but suddenly be in motion
2. the force of gravity diminishes with distance as 1/d^2 where "d" is the distance between the centers of any two gravitating bodies: earth and an apple on the one hand, or earth and the moon on the other.
GRAVITY AND THE THRID LAW OF MOTIONbecause the moon has a mass (although small compairativly) it causes the earth to wobbel in and out of its orbit around the sun, always pulling towards the side the moon is on- newton's second law f=ma and thrid law for interaction
THE LAW OF UNIVERSAL GRAVITATION
law of gravity: every object in the universe attracts other objects by a long-range gravitational interaction that obeys Newton's Third Law. The strength of the attractive force, F, varies with the masses. M and m, of the two objects and teh distance, d, between their centers according to teh relationship [f=GmM/d^2]
gravitational constant: (represented by G) number relating the strenght of the gravitational force to the masses being attracted and their distance apart (very small 6.67x10^-11) the gravitation force between 2 100-kilogram balls placed 30 centimeters apart is 1millionth of a pound- if one of the interacting objects has a large mass, like earth, does the force become appreciable.
Henry Cavendish: british scientist knkown for his work with hydrogen and his experiment that measured the gravitational force between two masses in order to calculate the density of the earth (2 small gold/platinum spherees mounted on opposite ends of a lightweight metal bar suspended in teh middle by a very fine wire. the wire has a mirror mounted in the middle of it. a focused light beam reflects off the mirror and onto a scale across the room. 2 large lead spheres were brought near teh small spheres, te gravitational attraction between teh samll and large spheres twisted teh wire just enoug to move the light spot on the scale. force required to twist the wire was determined, teh force between teh large and small spheres was inferred, adn the universal law of gravitation was used to calculate G
ACCELERATION REVISTED
force of gravity is increases as the objects gets closer (ball falling off a cliff will be stronger near the base of the cliff)even a cliff 10 miles high, the difference in the force of gravity and resultant acceleration is not significant

[G (mass of Earth)][1kg][0.0027] [G (mass of Earth)][1kg] =difference in the -________________________________ - _______________________ foce felt by 1-kilogram (6378)^2 (6379)^2 newtons rock between
top/bottom of cliff

only consider the 1/d^x decrease for objects like rocket ships, satellites, and the moon
treating a value as constant because it does not change significantly over teh area of interest is a common practice in science
GRAVITY AND CURVED SPACE-TIME
General Theory of Relativity (from Albert Einstein): description of gravity taht was published in 1915. this theory explains the relationship between teh geomtry of space and teh flow of time in our Universe
ways to measure gravity
1. Newton's second law F=ma, mass to be measured by seeing how an object accelerates when pushed
2. Newton's law of gravity, mass to be measured independently through force Earth exerts on it
Nothing in Newton's lwas requires taht those masses have the same value- guided by Occam's razor, hypothesized those masses are the same
gravity: a geometric effect arising from connection between space, time, and matter
space and time: space-time (ruber sheet across a frame and a heavy ball in the middel. the ball bearing causes teh sheet to sag so that a small bead rolling on the edge will naturally curve around in a circle- moon around the sun)