MR. HOLL S PHYSICS FACTS MECHANICS. 1) Velocity is a vector quantity that has both magnitude and direction.

Transcription

1 MR. HOLL S PHYSICS FACTS MECHANICS 1) Velocity is a vector quantity that has both magnitude and direction. 2) Speed is a scalar quantity that has ONLY magnitude. 3) Distance is a scalar and represents the total ground covered. 4) Displacement is a vector that represents the straight line distance from where you started to where you finished. (IT CAN BE ZERO) 5) Acceleration of a projectile on EARTH is always 9.8 m 2 and points down even at the highest point. The force also points DOWN. 6) Inertia is the same as MASS. 7) The x-direction or horizontal component of the velocity can be found using cosine (angle). This formula is on the reference table!!! 8) The y-direction or vertical component (up and down) velocity can be found using sine (angle). This formula is also on the reference table!!! 9) Projectiles will ALWAYS have a constant x-direction velocity. The y- direction velocity will change because of gravity. (t up = t down) 10) The initial y-velocity of a horizontal projectile is ZERO. 11) The initial x-velocity DOES NOT affect the time it takes a horizontal projectile to hit the ground. 12) MASS does not change when on object is moved to another planet. 13) Mass is measured in kilograms (kg). s

2 14) Weight is measured in Newtons (N). It is a force. 15) Mass to weight multiply by ) An object s weight can change when taken to another planet. Use the formula W = mg. Remember that g is not 9.81 here!!! 17) Two vectors will produce a maximum when the angle between them is 0 degrees. (ADD THEM) 18) Two vectors will produce a minimum when the angle between them is 180 degrees. (SUBTRACT THEM) 19) A force can produce equilibrium if it is less than or equal to the maximum resultant or greater than or equal to the minimum resultant. 20) The resultant is the addition of two or more vectors. 21) Vectors can be added using the head to tail method. Do this by starting the second vector at the end of the first vector. 22) Equilibrium means that Fnet = 0 and there is no acceleration. This can occur when an object is at rest or moving with constant velocity. 23) The GRAVITATIONAL force is ONLY a force of attraction and is 2 inversely proportional to r. ( r 2r, F 1/4F) 24) For any object moving at constant velocity, the force of friction is equal to the applied force. (Coefficients of friction can be found on the reference table) 25) The force required to start an object moving (static friction) is greater than the force need to keep it moving at constant velocity (kinetic friction).

3 26) Impulse is equal to the change in momentum and has the same units. WATCH THE DIRECTION OF THE FORCE!!! 27) For any force there is an equal and opposite force. The size and mass of the two items does not have any impact on this. 28) Power is the rate at which work is done. Units are Watts or Joules/second. 29) When an object is lifted and the power or work is being asked, you must use the objects weight as the force. 30) Only the VERTICAL DISTANCE matters when an object is lifted and you are solving for the power or work. 31) The force applied to a spring with a hanging mass is the weight of the mass. 32) The x-term in any spring equation is the amount of stretch/elongation. 33) Gravitational Potential energy is the energy possessed by an object because of its height. (PE = mgh) As h increases, PE increases 34) Kinetic energy is the energy possessed by an object because of its velocity. (KE = 1/2mv^2) v 2v, KE 4KE 35) Mechanical Energy (PE + KE) is always conserved when there is no friction. (PE + KE = PE + KE) 36) The work done by friction is referred to as Internal Energy. 37) When friction occurs, Mechanical Energy decreases and Internal Energy increases.

4 38) Centripetal force and centripetal acceleration always point towards the center of the circle. 39) The velocity will always point tangent to the circle for centripetal motion. 40) The equilibrant force is equal in magnitude but opposite in direction to the resultant vector. 41) Momentum is conserved in ALL explosions and collisions. 42) For problems involving average force and time, you must use the impulse formula. (J = Ft = p) 43) The slope of a distance versus time graph is velocity. 44) The slope of a velocity versus time graph is acceleration. 45) The area under a force versus time graph is impulse. 46) The area under a velocity versus time graph is displacement. 47) The slope of a force versus elongation graph is the spring constant. 48) FORCE and ACCELERATION both point down at all times for any type of projectile motion. 49) Maximum time of flight and height occurs at a launch angle of 90 degrees and maximum range (displacement) occurs at a launch angle of 45 degrees. As the angle increases from 0 degrees the height and time of flight increase. Range increases until the angle is 45 degrees.

5 ELECTRICITY AND MAGNETISM 50) Wire resistivity s are found on the reference table. (Nichrome has the highest and silver has the lowest. 51) Wire resistance is proportional to the length and inversely proportional to the Area. (long, skinny wires = large resistance) 52) Resistivity cannot change!! It is a property of the metal. 53) Current is the rate of flow of charge. 54) In a parallel circuit the total resistance MUST be less than the smallest resistor. Adding resistors makes the total resistance decrease. 55) In a series circuit the total resistance increases as resistors are added to the circuit. 56) The slope of a voltage versus current graph is the resistance of the circuit. (THIS NEEDS TO BE A STRAIGHT LINE) 57) A variable resistor has a resistance that can be changed. 58) As the voltage applied to a resistor (constant R) increases the current also increases. As the voltage decreases, current decreases. 59) Resistance increases as the temperature of the wire increases. Resistance decreases as the temperature decreases. 60) When either resistance or voltage changes in a circuit, current is affected. (use V = IR) 61) All resistors in series have equal current (I). Also = to total current.

6 62) All resistors in parallel have equal voltage (V). Also = to total voltage. 63) An electron and a proton have equal amounts of charge. (1e = 1.6 E -19 C) 64) A coulomb is charge, an amp is current [coulomb/sec] and a volt is potential difference [joule/coulomb]. I = q/t, V = W/q 65) An ev (electron volt) is a unit of energy ( 1 ev = 1.6E-19 J). The work done moving 1 electron through a potential difference of 1 volt is 1 ev. (W=Vq) 66) When charged spheres touch each other add the charges and divide by the number of spheres to find the final charge on each sphere. 67) Electric Fields point in the direction that a POSITIVE particle would move. Field direction is away from positively charged objects and towards negatively charged objects. Electrons will move in a direction OPPOSITE to the electric field. 68) When an object gains electrons its charge becomes negative. When an object loses electrons its charge becomes positive. 69) An object can ONLY gain or lose charge in whole number multiples of 1.6 E -19 C. Electrons cannot be split!! 70) Ammeters must be connected in series and voltmeters must be connected in parallel. 71) Magnetic fields point from the north to the south outside the magnet and south to north inside the magnet. 72) Electrostatic force can be repulsive or attractive depending on the two charges. Electrostatic force and electric field decreases as the distance increases. Graph:

7 LIGHT/WAVES 72)All electromagnetic waves originate from accelerating charged particles. 73) Sound waves are longitudinal and mechanical. Light waves are transverse and electromagnetic. 74) Light slows down, bends toward the normal and has a shorter wavelength when it enters a higher (n) value medium. (FAST - SOFA) (n values can be found on the reference table) The bigger the n value the SLOWER light will travel in that medium. 75) All angles in wave problems are measured to the normal. 76) Sound waves CANNOT travel in a vacuum or be polarized. Sound (longitudinal waves) need a medium to travel through. The speed of sound can be found on the reference table (331 m/s) 77) The electromagnetic spectrum (electrical, radio, microwaves, infrared, visible, ultraviolet x-ray and gamma or ERMI VUX G) are listed lowest energy/lowest frequency, highest wavelength to highest frequency/energy, lowest wavelength. (The electromagnetic spectrum is on the reference table) 78) The amplitude of a sound wave determines its energy and loudness. The amplitude of a light wave determines its brightness. 79) The speed of ALL types of electromagnetic waves (light waves) is 3.0 x 10 8 m/sec in a vacuum. 80) FAST SOFA refers to the refraction of light waves when they travel from one medium to another. (Fast To Slow Towards, Slow to Fast Away)

8 81) The keywords for any question involving resonance are VIBRATIONS and NATURAL FREQUENCY!! 82) Constructive interference occurs when 2 waves meet crest to crest or trough to trough. ADD the amplitudes and get brighter light or louder noise!! (0 degree phase difference or whole number wavelengths apart) 83) Destructive interference occurs when 2 waves meet crest to trough. SUBTRACT the amplitudes and get dimmer light or softer noise!! (180 degree phase difference or ½ wavelengths apart) 84) Diffraction effects are greatest for a LONG wavelength and a SMALL opening. 85) Two points are in-phase if they have the same displacement and direction of motion and are separated by a whole number of wavelengths. They are out of phase if they have opposite displacement and opposite directions of motion. 86) Period is inversely proportional to frequency. As period increases, frequency decreases. ( T = 1/f) The product of period and frequency is 1. 87) Period, velocity and wavelength are directly proportional to one another. If the period doubles, or the velocity doubles the wavelength also doubles. 88) When a wave travels from one medium to another, some of the wave is refracted and some of it is reflected. When a wave refracts there is a change in velocity and direction. (Note: if the wave is on the normal line it will NOT change directions.) 89) At the critical angle a wave will be refracted to 90 degrees. 90) Wave behavior of light and small particles (electrons) are proven by diffraction, interference and the polarization.

9 91) Transverse wave particles vibrate back and forth perpendicular to the wave direction. 92) Longitudinal wave particles vibrate back and forth parallel to the wave direction. 93) Diffuse (scattered) reflection occurs from dull or rough surfaces while regular reflection occurs from mirror (smooth) type surfaces. 94) According to the Doppler Effect, if a wave producing source is moving towards you, you will experience waves with a HIGHER frequency and a shorter wavelength. Also remember Red Run Away, Blue Come and Play. 95) In order for a standing wave to be produced there must be two (2) waves traveling in opposite directions that have the same amplitude and frequency. 96) Period is defined as the time for ONE cycle or wavelength. 97) When 2 waves interfere with one another they will continue on with their original size and direction after the interference occurs. MODERN PHYSICS 98) Light exhibits both WAVE and PARTICLE properties. 99) Diffraction and interference prove wave properties and momentum and the photoelectric effect prove particle properties.

10 100) Particles (electrons) can exhibit WAVE characteristics. 101) Photons have both energy and momentum!! (E = hf = hc/ ) Energy is proportional to frequency and inversely proportional to the wavelength. 102) A photon is ABSORBED when an electron moves up an energy level and a photon is EMITTED when an electron moves down an energy level. 103) In order for an electron to change energy levels, the photon MUST have an energy that is equal to the difference between any 2 energy levels. 104) In order to ionize an atom, the photon MUST have the ionization energy. If it has less than the ionization energy nothing will happen. 105) Lost mass gets converted into energy. Formula: 2 E mc 106) 1 universal mass unit (1 u) is equal to 9.31 E 2 MeV. Convert u to MeV 107) When a particle is annihilated ALL of its mass is converted into energy. 108) The strong nuclear force holds protons and neutrons (aka nucleons) together. It is a force of attraction!! It is the strongest force in the universe and it acts over a very short range. 109) The electrostatic force holds protons and electrons together because they have opposite charges. 110) Protons and neutrons are examples of baryons.