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Physics Exam Study Notes ALL info check it out
Typology: Exams
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● Kinematics: study of motion ● Basic types of motion: o Uniform (constant speed in straight line) o Non-uniform ● Scalar quantity: with magnitude & no direction o Distance, average speed ● Vector quantity: with magnitude (arrow above it) & direction (in square brackets after unit) o Position, displacement, acceleration ● Velocity: o Rate of change of position o Average velocity: displacement divided by time interval for that change o 2-D motion: using GPS (global position system) ▪ N/S/E/W to communicate directions ▪ Ex : 5.0 cm [25° S of E] or [E25°S] ● Acceleration: rate of change of velocity ● V-t graph to find other things: o Area under line gives displacement, slope gives acceleration ● Resultant displacement of 2 dimensions: o Vector sum of individual displacements o Use Pythagorean Theorem and SOH-CAH-TOA ● Relative motion: velocity of a body relative to a particular frame of reference ● Methods of writing direction: o GPS = [E25°S] or [25° S of E] o Bearing = [N 160°] (measure CW from North position)
● Dynamics: causes of motion ● Force: push or pull, vector quantity o 4 fundamental forces: gravitational, electromagnetic, strong nuclear, weak nuclear ● Unit of force: Newton (N) -> 1N = 1(kg x m)/s^2 ● Net force/resultant force: vector sum of all forces acting on an object ● Mass: quantity of matter in an object (standard: kg) ● Weight: force of gravity on an object (Fg), measured in Newton’s Newton’s Laws of Motion:
● Gravitational potential energy: energy possessed by an object because of its position relative to a lower position ● Kinetic energy: energy possessed by an object due to its motion ● Law of Conservation of Energy: energy cannot be created nor destroyed. When energy changes from one from to another, no energy is lost. o Valley problems, pendulum problems, objects dropped from a height ▪ (mvA^2 )/2 + mghA = (mvB^2 )/2 + mghB o Ramp problems
remains constant
Vibrations: ● Vibration: periodic motion when it repeats a pattern of motion ● 3 types of vibrations: o Transverse: perpendicular to its axis at normal rest position (ex. pendulum) o Longitudinal: parallel to its axis of rest position (ex. pogo stick) o Torsional: around its axis at rest position (ex. motion of steering wheel) ● Cycle: 1 complete oscillation or 1 complete vibration/1 complete wave ● Frequency (f): # of cycles per second, measured in Hertz (Hz) ● Period (T): time for 1 cycle, measured in seconds ● Amplitude: distance in either direction from the rest position to an extreme position (max displacement) ● In Phase: objects have same period & pass through the rest position at the same time ● Out of Phase: objects don’t have the same period & pass through the rest position at the same time Waves: ● Wave: vibration/disturbance that can transfer energy over a distance ● Transverse waves: particles in the medium vibrate at right angles to the direction in which the waves travel (ex. water waves/waves in a rope) o Crest/trough, node/antinode, amplitude, rest axis ● Longitudinal waves: particles vibrate parallel to the direction of wave motion (ex. sound waves/compress coils in a Slinky) o Compression/rarefaction ● Wave interference: occurs when 2 act simultaneously on the same particles of a medium o Constructive interference: creates supercrests and supertroughs (add 2 together) o Destructive interference: waves diminish one another, amplitude decreases
● Standing waves: special case of inference in a one-dimension medium o If colliding waves are controlled so they have the same amplitude and wavelength but in opposite directions, it results in a “standing wave interference pattern” ● Principle of Superposition: at any point, the resulting amplitude of 2 interfering waves is the algebraic sum of the displacements of the individual waves ● Resonance: response of an object that is free to vibrate to a periodic force with the same frequency as the natural frequency of the object o Mechanical resonance: if physical contact between the periodic force & the object o Ex: Tacoma Narrows bridge, rock a car stick in snow, child moving on swing Sound: ● All sounds stimulate the auditory nerve ● Humans respond to sound frequencies between 20Hz – 20,000Hz o Infrasonic: lower than 20Hz, ultrasonic: above 20,000Hz ● Produced by vibrating objects (ex. guitar string, throat vibrating, stereo speaker) ● Needs a material medium for transmission ● Sound waves are longitudinal waves ● Larger amplitude: louder sound, higher frequency: higher pitch ● Intensity of sound: o Sounds audible to humans can vary in intensity ● Loudness measured in bels (B), most people use decibel scale (dB) o 1dB = 1/10B or 10dB = 1B ▪ 0dB: threshold of hearing (10-12W/m^2 ) ▪ 85dB: must wear eat protection for industrial safety ▪ 130dB: threshold of pain (10^1 W/m^2 ) ▪ 160dB: instant perforation of ear drum (10^4 W/m^2 ) o Each rise of 10dB: 10 fold increase in sound intensity ● Interference between identical sound waves: causes louder/softer sound regions o Can be done with 2 loudspeakers in phase ● Noise cancellation headphones use destructive interference (exactly out of phase with outside noise), can remove 70% of external noise ● Beat: periodic change in sound intensity ● Beat frequency: # of beats heard per second, in hertz ● Doppler Effect: observed frequency increases when source of sound approaches, and vice versa Sound Barrier: ● When flying at speed of sound, the wave fronts in the front of a plane pile up, producing an reap of very dense air/intense compression o Extra thrust required to break through barrier
Quality of sound: ● In a vibrating stretched string and the fundamental mode of vibrating, the string vibrates in one segment with a node on each end and one antinode in the middle. This creates f 0 or fundamental frequency. ● Different frequencies can be produced by forcing the string to vibrate in different patterns o Frequency produced depends on number of nodes/antinodes ● Second harmonic (2f 0 ) same as first overtone, 3 f 0 = second overtone, etc. o Frequencies of overtones are in simple whole numbered multiples of the fundamental and are called harmonics o Overtones can be more intense than fundamental in some instruments (ex. clarinet) ● Quality of a musical note depends on the # and relative intensity of the overtones it produces along with the fundamental ● Tuning fork only has one fundamental frequency Resonance in air columns: ● Closed air columns: o Caused by standing wave pattern with node at closed end & antinode at open end o For fixed length: resonance first occurs when air column is ¼ λ (wavelength) ▪ Then: 3/4 λ, 5/4 λ, 7/4 λ etc. ● Open air columns: o Created by standing wave patterns set up in a tube where an antinode exists at BOTH open ends o For fixed length open columns: resonance first occurs at λ/2 (first harmonic) o Then: λ, 3λ/2, 2 λ, etc.
Electrostatics: ● Static electricity: a build-up of stationary electric charge o Charging by friction: rubbing 2 objects together ● Fundamental laws of electric charge: o Opposite charges attract, similar charges repel, charged objects attract some neutral objects ● Change in charge due to loss/gain of electrons only ● Conductors: solids in which charge flows freely (most metals, water) ● Insulators: solids that hinder the flow of charge (glass, rubber, wood, plastic, concrete) Electric fields and electric charge: ● Every charged object creates an electric field of force in the space around it
o Relative distance between adjacent field lines at a given point is an indication of the strength of the electric field at that point ● Magnitude of the electric force of the attraction or repulsion is: o Directly proportional to the product of the charges o Inversely proportional to the square of the distances between them ● One coulomb (C) of energy made up of 6.24x10^18 e- Electric current: ● Rate of movement of electrically charged particles past a point ● When electric charges move from 1 place to another ● In metals: moving charges are electrons ● Measured in amperes (A) o 1A = 1C/s o Standard household fuse: 15A ● Conventional current: positive charge from + to – (used in this course) o Electric flow: negative charge from – to + ● Can flow in either direction in liquids & gases ● Batteries: DC, wall sockets: AC ● Ammeter: measures amount of electric current in a circuit Electrical potential difference: ● Amount of work required per unit of charge (coulomb) to move a positive charge from one point to another in the presence of an electric field ● A 1V battery performs 1J of work to move 1C of charge between its terminals o 1V = 1J/C Electrical resistance: ● Opposition experienced when charges pass through a material or device, resulting in a loss of electrical potential energy ● Ohm’s law: The potential difference between any 2 points in a conductor varies directly as the current between the 2 points as long as the temp. remains constant. ● Unit for resistance: ohm (Ω) o 1 Ω = 1V/1A Electric circuits: ● Series: o VT = V 1 + V 2 + V 3 o IT = I 1 = I 2 = I 3 o RT = R 1 + R 2 + R 3 ● Parallel: o VT = V 1 = V 2 = V 3
▪ Domains: clusters of 10^17 atoms ● Non-magnetized: randomly pointing domains ● Effects: o Magnetic induction ▪ Permanent magnet near iron nail: temporary magnet ▪ Field of perm. cause dipoles in nail to align momentarily ▪ Soft iron: if nail loses magnetism as moved away ▪ Hard iron: if nail retains magnetism as moved away o Demagnetization ▪ Aligned dipoles return to random directions ▪ Caused by dropping or heating ▪ Some materials revert when removed from magnetic field (i.e. pure iron) ▪ Materials that instantly demagnetize: soft ferromagnetic materials ▪ Alloys used to make hard ferromagnetic materials (use aluminum or silicon) o Reverse magnetization ▪ Poles reversed when magnet placed in a strong enough magnetic field with reverse polarity o Breaking a bar magnet ▪ Creates mini magnet with identical dipole alignment o Magnetic saturation ▪ Peak of magnet’s strength: when max # of dipoles aligned o Induced magnetism by Earth ▪ Dipoles will align if a piece of iron with agitated atoms by heating or mechanical vibration in Earth’s magnetic field ● Point north & at angle of inclination + tapping with a hammer ▪ Steel columns, hulls, and railroad tracks tend to magnetize o Keepers for bar magnets ▪ Bar magnets demagnetize over time as poles start to reverse the dipoles’ polarity (random thermal motion of atoms) ▪ Store in pairs with opposite poles adjacent & small pieces of soft iron (keepers) across ends to prevent demagnetization ▪ Keepers become strong induced magnets, form closed loops
Factors affecting the magnetic field of a coil: ● Coil’s magnetic field can be turned on/off & alter strength ● Strength related to degree of concentration of its magnetic field lines ● More current in the coil = greater concentration of magnetic field lines in the core o 2x current = 2x magnetic field strength ● Number of loops in the coil: o Each loop of wire produces its own magnetic field o Magnetic field of a coil: sum of the magnetic fields of all its loops o 2x loops in coil = 2x magnetic field strength ● Type of core material: o Material of core affects coil’s magnetic field strength ▪ Cylinder of iron (instead of air) = 1000+ times stronger ▪ Aluminum core = no effect o Core material becomes induced magnet, magnetic field strength increases ▪ Dipoles align with magnetic field of the coil o Relative magnetic permeability (K): factor by which a core material increases the magnetic field strength that would exist in the same region if a vacuum replaced it o 2x relative magnetic permeability of the core = 2x strength ● Ferromagnetism, paramagnetism, and diamagnetism o Core materials divided into 3 groups according to their relative magnetic permeability o Ferromagnetic: high, strong induced magnets o Paramagnetic: slight increase, slightly greater than 1 ▪ Oxygen and aluminum o Diamagnetic: slight decrease, slightly less than 1 ▪ Copper, silver and water Motor Principle: ● A current carrying conductor that cuts across external magnetic field lines, experiences a force perpendicular to both the field lines and the direction of the electric current ● Applications: moving coil loudspeaker, galvanometer (armature forced to pivot with increased current) o Voltmeter: galvanometer + high value resistor in series o Ammeter: galvanometer + low value “shunt” resistor in parallel ● Electric motor: device that can convert electrical potential energy into mechanical energy o DC motor: needs DC electricity, uses “split right commutator” to reverse current through armature o AC motor: needs AC electricity, uses “slip rings” attached to armature since current switches direction, no need for split ring
● Step down transformer: o Used to decrease AC voltages o Ex: train set, car race car transformers, power adapters ▪ Adapter : step down transformer + rectifier (AC to DC convertor) in series