MCAS/FINAL PHYSICS REVIEW

Isotopes

atoms with an unequal number of protons and neutrons (usually more neutrons)

fission

the process where a heavy, unstable atomic nucleus splits into two or more smaller, lighter nuclei

• ex: large unstable isotope is hit by high-speed particles

• energy (light and theral energy is released)

• requires less energy then fusion

fusion

the process where two or more light atomic nuclei slam together to form a single, heavier nucleus

• under extreme pressure and temperature

• requires large amount of energy (in sun) and releases some

radioactive decay/nuclear decay

isotopes change by themselves and become more stable

• breaking into smaller atoms/particles

• influenced by atomic # & mass

• types: Alpha, Beta, Gamma

alpha decay

atom breaks into two parts and emits an helium

• pair of neutron bound to pair of protons

• smaller atom (whatever is left over)

• MN decrease by 4 and AN decrease by 2 (turns into diff element)

• release large slow-moving decay products

beta deacy

neutron turns into proton & releases electron to balance

• turns into different element

• AN increase by 1

gamma decay

emits gamma ray & rearranges protons & neutrons

• highest energy

• no change in AN & MN and stays the same element

half life

amount of time for a radioactive substance to lose half its mass through decay

atom

center = nucleus

• protons (positive)

• neutron (neutral)

electrons (negative) float around the nucleus

charges attraction

+ + = repel

- - = repel

+ - = attract

conductors

materials that transfer electrons easily

• ex: metals, salt water, humid air

insulators

materials that do not transfer electrons easily

• they can store electrons

• ex: wood, plastic, rubber, thick fabric, dry air

Coulomb's Law

electrostatic force between electrically charged particles

• like charges repel and opposite charges attract

• with a force directly proportional to the product of the charges

• inversely proportional to the square of the distance between

Electrostatic force

the attractive or repulsive force that acts between electrically charged particles or objects at rest

• Distance increases = Fe decreases

• Charge increase = Fe increase

electric field

positive = outward arrows

negative = inward arrows

stronger charge = more arrows

repulsive electric fields

• same charges repel (+/- & +/-)

• field lines push away from each other

attracive forces

opposite charges attract, their field lines connect

electrical circuit

a closed loop through which electrons (electric charges) flow

Ohm’s Law

• relationship between voltage, current and resistance

• V = I x R

• R = resistance (ohms)

• I = current (amps)

• V =voltage (volts)

Power (P)

the rate that electrical energy is converted into a different type of energy

• P = I x V

• units = watts or J/s

mechanical waves

• require a medium (ex: sound, earthquakes) and vibrate matter

• multiple styles: longitudinal, transverse, and more

• fastest in solid, slowest in gas

electromagnetic waves

• light waves: don’t need matter to move (can travel through empty space)

• only transverse

• made from photons and the fastest thing in the universe

• ex: light, x-rays, gamma ways, UV rays

• constant speed: 3 × 10^8

transverse waves

particles vibrate perpendicular

longitudinal waves

particles vibrate parallel to wave direction

wave velocity

V = F x λ

λ = wave length

F = frequency

V = velocity

• higher frequency = shorter wave length (vice versa)

Pitch

pitch = frequency

• more matter thats being vibrate, the lower the pitch

Sound

• mechanical waves

• longitudinal waves

Doppler Effect

• sound moving towards you is louder (higher frequency and less wave length)

constructive interference

When two waves meet and add together

• crest + crest = bigger crest

• bigger wave (amplified)

• higher amplitude, concentrated energy in one place

• in water = bigger wave, in light = light

Destructive interference

When two waves meet and cancel out

• smaller wave or even zero

• Lower amplitude, Can completely cancel if equal size“, “Muted” wave

• in water = no wave, in light = dark

• Noise cancelling headphones match the frequency and create the same wave but opposite

EM Wave Order

Law of Reflection

The Reflected Angle for a single ray must equal its Incident (orginal) Angle

Specular Reflection

Light that is reflected in the same direction from a smooth surface (like a mirror)

Diffuse Reflection

light that is reflected in many directions from a rough surface

• can cause reflection to be blurrier

concave mirror

A mirror that curves inward (like the inside of a spoon) and can form images that are magnified or upside down depending on distance.

• stuff look bigger when close

• smaller and upside down when far

convex mirror

A mirror that bulges outward (like the back of a spoon) and always forms a smaller, upright image.

refraction

waves bend and change direction as they go from one medium to another

Less refractive to more refractive

• light ways get bent towards the normal

• light slows down

More refractive to less refractive

• light rays bent away from normal

• light speeds up

Temperature

average kinetic energy is represented by temperature

• higher temperature = more kinetic energy

Heat/Thermal Energy

energy that moves from a warmer object to a cooler one

• measured in Joules

Conduction

heat moves through a substance in physical contact

• stick on candle flame

Convection

heat moves through a mixing or circulating fluid

• boiling water

Heat Transfer

Thermal Equilibrium

is when two or more objects in contact have reached the same temperature, so no heat flows between them anymore.

• heat always move from hot to cold until they reach Thermal Equilibrium

• one substance gains heat from another, the other substance loses that heat

Adding Heat

• attractive forces weaken, kinetic energy increases

• melting, vaporization

Removing Heat

• attractive forces strengthe, kinetic energy decreases

• freezing, condensing

Phase Change

Heat is the “cost” or energy needed to change the phase of a substance (solid ↔ liquid ↔ gas).

• It doesn’t raise temperature during the change

• Instead, it breaks or forms bonds between particles

• More heat = more phase change, not hotter temperature

Work

energy transfered in or out of an object

W = F x D

mechanical energy

energy that allows an object to do work

ex: kinetic and potential energy

potential energy

energy that is stored due to an object's position or condition.

PE = mgh

Gravitational potential energy

stored energy an object has because of its height above the ground (or another reference point).

kinetic energy

the energy an object has because it is moving.

KE = ½ mv²

translational kinetic energy

 energy due to motion from one location to another

Law of conservation for Energy

all forms of energy can be converted into a different form

• potential energy decreases it becomes kinetic energy and vice versa

Total Mechanical Energy

Add Kinetic and Potential Energy

• total mechanical energy doesn’t change

Power

the rate at which work is done

• unit watts or J/S

• P = W/change in time

Energy Efficiency

a measure of how much input energy is converted into useful output energy.

• Efficiency = Energy Out/Energy In

momentum

the quantity of motion an object has based on mass and velocity

p = m x v

m = mass v = velocity

measured in kg x m/s

elastic collison

two objects hit eachother and bounce off eachother

m₁v₁ + m₂v₂ = m₁v₁' + m₂v₂'

inelastic collision

The two objects, m1 and m2, have the same velocity when they are stuck together, v'

m1v1 + m2v2 = (m1 + m2)v'

Law of Conservation of Momentum

total momentum of a group of objects doesn’t change (unless acted on by an outside force)

impulse

the change in momentum of an object when a force acts on it for a certain amount of time.

Δp = F_Net(Δt) 

• large impulse = large forcer over short time

Fnet

Net force is the overall force acting on an object after all forces are added together (with direction).

Fnet = m x a

• m increases = a decreases

• a increase = fnet increase

distance

the length of the path something takes

• always postive

displacement

measurement of the space in between the start and finish

• negative, positive, zero

• Δx = x_f - x₀ 

velocity

displacement/change in time

• m/s

speed

distance/change in time

acceleration

the rate at which an object’s velocity changes over time.

a = change in velocity/change in time

gravity

when objects fall they accelerate at 9.8 m/s² due to the pull of gravity

Newton’s 1st Law

An object will stay at rest or keep moving in a straight line at constant speed unless acted on by a net force.

• Law of Inertia = property of an object that resists change in motion (more mass = more inertia)

Newton’s 2nd Law

Fnet = M x A

• more mass = less accerlation

• more force = more accerlation

example:

• It’s easier to push an empty cart than a full one

Newton’s 3rd Law

For every force, there is an equal and opposite force.

• gravity opposite of normal force

• applied opposite of friction

Free Body Diagrams

• Fn = Fg

• Fg = weight/the force of gravity pulling dowwn

• Fnet = Fa - Ff

static friction

between two things that grip eachother but don’t move

kinetic the friction

between two things that are currently sliding against each other

coefficent of friction

number that tells you how “rough” two surfaces are and how much they resist sliding past each other.

• Bigger μ → more friction (harder to slide)

• Smaller μ → less friction (easier to slide)

It has no units (just a number).

• μ = Ff/Fn

Fg = m x g

weight/force of gravity on Earth

Universal Law of Gravity

• M increase = Fg increase

• Distance increase = Fg decrease

• G = 6.7 × 10^-11

Kinematic Graph

Displacment on Velocity over Time Graph

light particles

photons—discrete, zero-mass packets of energy. The most famous demonstration of this particle nature is the Photoelectric Effect, where individual photons collide with electrons to knock them out of metal

Diffracted

a wave spreads out when it passes through a small opening or around an obstacle.

Refracted

means light (or a wave) changes direction when it passes from one medium to another because its speed changes.