Physics--Things you need to know (definitions/important things to remember)

DONE SO FAR: Topic A (ONLY UNTIL POSTULATES OF RELATIVITY), Topic B, and Topic C

Projectile motion:

when is initial velocity 0?

when object is dropped from rest

NOT when it’s launched at an angle or horizontally

UCM: acceleration of an object moving with UCM

always toward center of circle

always changing, because direction of speed always changes. Speed is constant.

UCM: velocity of an object moving w UCM

tangentual to circle of motion of object. a and v are always perpendicular

When does UCM happen?

when object has constant speed and moves in a circular path.

Projectile motion: What’s special about horizontal velocity?

it stays constant throughout all ideal projectile motion

Air resistance

when forces balance, an object reaches terminal velocity.

Constant force object falls with when net force=0

as drag force increase, magnitude approaches weight of object

When can you use suvat

when acceleration is constant

can static friction be bigger than kinetic friction

yea

what direction is elastic force

it is restoring: always points to equilibrium position.

Newton’s first law

An object will remain in translational equilibrium unless acted upon by a net (unbalanced) force.

Newton’s Second Law

The net force acting on an object is equal to the rate of change of the object’s momentum (F=ma)

Newton’s Third Law

When one object exerts a force on a second object, the second object simultaneously exerts a force equal in magnitude and opposite in direction to the first object.

2 Postulates of Special Relativity

the laws of physics are the same in all intertial frames of reference (no acceleration)

the speed of light in a vacuum is constant for all intertial frames.

Assumptions for an ideal gas

the moldecules undergo perfectly elastic collisions (no loss of momentum/KE)

there are no intermolecular forces between the molecules

molecules are in constant random motion

gas contains a large number of identical particles

particles occupy negligible volume in the container

Real gas will approximate an ideal gas when…

pressure of the gas is low

density of the gas is low

temperature of the gas is moderate to high

What is internal energy of ideal gas

all random kinetic energy

no intermolecular forces, no potential energy in gas phase

Gas Laws

Boyle’s law—-P and 1/V (isothermal) are a curved line down

Charles’ Law—-V and T (Isobaric) is straight line up

Amonton’s Law—-P and T (isochoric) is a straight line up

Luminosity

power output of an object emitting thermal radiation

Temperature

measure of the average random kinetic energy of the particles of a substance

This is a macroscopic property: no single particle has temp.

Internal energy

total intermolecular potential energy added to the random kinetic energy of the molecules of a substance

what is heat

synonym for thermal energy, measured in Joules

NOT TEMP

NOT INTERNAL ENERGY

intermolecular potential energy and random kinetic energy

Intermolecular PE is due to phase

random KE is due to temp

How does the internal energy of an ideal gas differ from that of a real gas?

internal energy of ideal gas relies only on temp (KE).

Real gas’s internal energy also relies on pressure and volume (intermolecular forces, potential energy)

Thermal Radiation

electromagnetic radiation generated by the thermal motion of microscopic particles

Thermal capacity

energy required to raise the temperature of an object by 1 Kelvin

Specific heat capacity——aka “c”

energy require to raise the temperature of a unit mass of a substance by 1 Kelvin (for 1 KILOGRAM)

Specific Latent heat

energy required to change the phase of a unit mass of a substance WITHOUT changing its temp

latent heat of vaporization = liquid/gas

latent heat of fusion = solid/liquid

When heat is transferred to a substane, it will either increase temp OR change phase, NEVER BOTH

Emissivity

measure of how effectively an object radiates or absorbs thermal energy

ranges from 0-1

perfect absorber of radiation will also be perfect emitter

Black Body (radiator)

an ideal object/surface with an emissivity of exactly 1

wide spectrum of EM is emitted (distribution and intensity depend on temp)

wtf is Solar Constant!

mean solar radiant power per unit area arriving at Earth’s Upper atmosphere (2D disc)

Greenhouse effect

Natural frequency (resonant frequency, sm that all objects have—-freq they naturally vibrate at) of most greenhouse gases is in the Infared wavelength range.

GHG will readily absorb IR radiation, then re-radiate it in random directions (DO NOT say REFLECT)

due to resonance, Earth absorbs some light passing through atmosphere and re-radiates it. But, it can’t leave since GHG also re-radiate it in all directions

First law of Thermodynamics

Statement of conservation of energy

Q = change in U + W

Isothermal process

Temp remains constant U=0, Q=W

PV graph: curved line down, a bit higher than adiabatic

Isovolumetric process

volume remains constant W=PV, Q=U

PV graph: straight line down

Isobaric process

pressure remains constant Q=U+W (normal)

PV graph: straight line across

Adiabatic process

no heat transferred Q=0, U=-W

PV graph: curved line down, a bit lower than isothermal

PV diagram

P is y axis

V is x axis

area under curve is work done on/by system in a thermodynamic process

Second Law of Thermodynamics

Kelvin ver: In a cyclic process, it is impossible to completely convert heat into work

Clausius ver: Thermal energy cannot spontaneously be transferred from a cold body to a hot body

Refers to the change in entropy of an isolated system

Entropy

measure of the disorder of a system

what is Heat engine

heat engine is a system that converts thermal energy into work

uses cyclical processes

Stirling Cycle

Isovolumetric heating by hot resevoir

gas expands isothermally, doing work on piston

isovolumetric cooling by cold reservoir

work done on gas by piston in isothermal compression

how to find work done by a heat engine

equal to the area enclosed by the cycle’s loop on a PV diagram

Carnot Cycle

idealized/hypothetical cyclical process that is more efficient than Stirling cycle (less waste heat)

uses reversible adiabatic processes

isothermal expansion at hot temp

adiabatic expansion from hot temp to cold temp

isothermal compression at cold temp

adiabatic compression from cold temp to hot temp

goes clockwise

SHM and Conditions

SHM is a type of oscillation that will create a pure sine/cosine wave

A restoring force (always directed towards equilibrium) causes this acceleration

Conditions for SHM:
Acceleration of object is proportional to its displacement from equilibrium

Acceleration of object is always directed towards equilibrium

How do PE, KE, and acceleration change at different points on the object’s path in SHM?

Acceleration is at maximum at maximum displacement or amplitude. Acceleration is zero at equilibrium.

Velocity is 0 at these maximum points. Velocity is greatest at equilibrium.

KE is 0 at maximum points, and greatest at equilibrium.

PE is greatest at maximum points, and 0 at equilibrium.

What affects period in spring-mass and pendulum systems?

mass, gravity, length of pendulum, and spring constant.

NOT DRAG, FRICTION, OR AMPLITUDE

What’s damping and what does it affect or not affect?

Damping is the decrease in an oscillating object’s amplitude over time due to energy losses.

DOES NOT CHANGE PERIOD

What does the a=-w²x graph look like??? (W IS NEGATIVE)

this

Transverse vs longitudinal waves

transverse waves oscillate perpendicular to the direction of travel of the wave. Crests and troughs are points of max/min displacement.

Longitudinal waves oscillate parallel to the direction of travel of the wave (sound waves, compressed slinky waves (slinky compressing and decompressing as medium oscillates). Compressions and rarefactions are points of max/min displacement.

Graphing waves: what are the two types of graphs?

Displacement-distance graph shows entire wave at a single instant in time. All particles are represented. USE FOR WAVELENGTH. CANNOT FIND PERIOD ON THIS GRAPH

Displacement-time graph represents displacement of a single particle in the wave. USE FOR PERIOD. CANNOT FIND WAVELENGTH

Pitch and Loudness of a sound

diagram

Reflection and Refraction (definitions)

Reflection is when some of the energy of a wave rebounds back into the original medium

Refraction is when some of the energy propogates into the new medium

What is diffraction!

When a wave passes through a narrow gap or slit, the waves spread out. Most extreme when the wavelength of the wave is close to the size of the opening/slit.

Waves can also diffract around obstacles.

Superposition + Interference

Principle of superposition: when two waves meet at a point in space, the total displacement is the vector sum of their individual displacements. (when two waves overlap and their displacements add together at the same point and time)

Interference is the result of superposition

Constructive vs Destructive interference

constructive is when waves meet in phase

destructive is when they meet out of phase

Path Difference

Difference in distance traveled by each wave from its source to the point of measurement

Integer = constructive

Half integer = destructive

Single Slit Diffraction Pattern

Pattern of bright and dark fringes

NOT interference pattern

Young’s Double Slit Experiment

slits produce coherent light (constant phase difference) for interference (MUST)

Two source interference creates bright and dark spots.

Also a single-slit diffraction pattern due to diffraction of each slit

Combination of 2 source and single slit diffraction

What happens as # of slits increases?

maxima become narrower, brighter, but have the same spacing.

diffraction grating

large number of equally spaced slits

when monochromatic, coherent light shines through a diffraction grating, a pattern of focused, bright maxima is seen.

what do diff harmonics of standing waves on a string look like?

like this

What do diff harmonics of standing waves in an open pipe look like?

this

What do diff harmonics of standing waves in a closed pipe look like?

this, and NO EVEN NUMBERED HARMONICS

How do standing waves form?

When two waves of equal AMPLITUDE, FREQUENCY, and SPEED pass through each other in OPPOSITE directions, a standing wave is formed by the superposition of the two waves.

Differences between traveling and standing waves

TRAVELING:

transfers energy between two points

all particles have same amplitude

any phase difference is possible between particles

STANDING:

have energy, but none is transferred

particles have diff amplitudes

two particles can only be completely in phase or completely out of phase

RHR #1: (the one w velocity)

Thumb= Force on a POSITIVE charge

Index= velocity

Middle= B field (magnetic)

RHR #2: thumb curling thing

Thumb= direction of current

Finger curl direction= B field direction

How to find impulse on a graph

area under curve on a Force-Time diagram

Law of Conservation of Momentum

Momentum of a system does not change so long as no net external force acts on the system.

Elastic vs. Inelastic collision

Elastic: kinetic energy is conserved

Inelastic: kinetic energy is NOT conserved (lost to heat, sound, etc.)

Momentum still conserved for both.

Explosions are REVERSE collisions. Initial momentum is usually zero.

What is work?

Energy that is added or removed from the system, when applying a force

aka change in E

unit: J

How to find work on a graph

Area under the curve of a force vs. displacement graph

What is power

the rate at which work is done (change in W)/(change in time)

unit is Watts.

W=J/s

Rotational motion analogies (variables)

this

what is torque

torque is the rotational equivalent of a force. Will cause rotational acceleration about a pivot

Rotational equilibrium

in equilibrium if the net torque acting on the object is zero.

Wtf is inertia!

The moment of inertia describes an object’s resistance to rotation.

Based on how mass is distributed about its axis of rotation (closer = less inertia)

Conservation of Angular Momentum

The angular momentum of a system does not change unless a net external torque acts on the system.

What is impulse

A change in momentum

equation for centripetal force

RADIAL DIRECTIONS: towards center = positive, AND away from center = negative

Total Energy of an object in orbit, and what happens to it

if total energy is positive, object follows a hyperbolic path and never returns

If total energy is zero, object follows parabolic path, where it just about stops. Never returns.

If total energy is negative, object goes into circular or elliptical orbit (or crashes into planet if launch speed is too low)

Gravitational Potential

work done per UNIT MASS (J/kg) to move a SMALL TEST MASS to a point from infinity

Graph of Energy for an orbiting mass

this

Total orbital energy

The total orbital energy is negative—-the object is bound by the grav. field of the planet

Gravitational potential energy (of an object)

Energy that an object has due to its position in a grav. field.

Defined as 0 at r = infinity

Grav. Potential energy is negative everywhere else

Electric potential energy (of a particle)

Energy stored in a charged particle based on its position in an electric field

also 0 at r = infinity

Electric Potential

Work done per UNIT CHARGE to bring a small TEST CHARGE to a point from infinity (J/C, aka Volt)

Electric field strength

Force per unit POSITIVE test charge at a specific point in an electric field

Gravitational field strength

Force acting per unit mass on an object at a specific point in a gravitational field

what happens inside a charged sphere?

ts

Galilean Relativity

Assumes that Newton’s laws of motion are the same in all inertial reference frames (frames that are not accelerating)

Inverse transformations (relativity)

this

Evidence for time dilation

Muons decay: and when they were moving at the speed of 0.994c relative to lab clocks, their average lifetime from the lab clocks agreed w the relativistic measurements.

Atomic clocks flown around the world also show evidence: time dilation is used to calibrate them when they move

Evidence for length contraction

Muons are produced when cosmic rays interact w the atmosphere. They should decay before reaching the Earth’s surface, according to classical physics, but we detect muons on the surface.

velocity when rolling

v = wr

0 at contact point, medium at center of mass, and fast at top

Electric Potential Difference

Work done per UNIT CHARGE to move a small POSITIVE test charge between TWO POINTS

V = W/q

Conductor vs insulator

the outer valence electrons of a conductor are very loosely bound to their nucleus. All electrons in an insulator are tightly bound to their nucleus.

Some materials can act as both, called semiconductors.

What is electric current

Rate of flow of charge (Amp, aka C/s)

ACTUAL flow of charge carriers (electrons) is opposite the direction of conventional current

What is resistance

A measure of its tendency to resist the flow of current

Ratio of the potential difference across a conductor to the current flowing through it (unit: Ohm)

What is resistivity

A property of a material that describes its natural resistance independent of its physical dimensions

Unit: Ohm x meter