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Physics Praxis Cheat Sheet by

Study guide for Physics Praxis 5266

Nature of Science: 15 questions, 12%

magnitude NO direction Ex= speed, distance
magnitude & Direction. Ex= accele­ration, displa­cement
Signif­icant Figures
all digits after the first non-zero are signif­icant
ex: 0.00410 3 sig figs, 23840100 6 sig figs
leading zeros don't count
adding round to # with the fewest decimals
ex:how close results are to the true value
how close results are to one another
Systematic Error
consistent error
W=mg=mass X gravity
W=Force x distance

Matter and Energy: 19 questions, 15%

Bohr model
electrons move in fixed orbitals (shells) and not anywhere in between and that each orbit (shell) has a fixed energy
alpha= 2p,2n bound
beta=high energy, high speed electrons
gamma=shortest wavelength electr­oma­gnetic waves
releases energy ex. atom smashing
releases energy ex. sun
Energy transfer
radiation= emitted
conduction= touch
convection= fluids
1st law= conser­vation of energy
2nd law= entropy increases
3rd law= A perfect crystal at zero Kelvin has zero entropy
Ideal Gas Law
Boyle's law PV=nRT
pressure and volume of a gas have an inverse relati­onship
Kinetic energy
energy of motion
Potential energy
stored energy
mgh=1/2mv+ mg(2R)
velocity b4 impact: square root (2gh)

Waves: 21 questions, 17%

Transverse waves
motion in which all points on a wave oscillate along paths at right angles to the direction of the wave's advance. Ex Water ripples
Longit­udinal waves
vibration of medium is parallel to the direction the wave travels and displa­cement of the medium is in the same direction of the wave propag­ation. Ex: sound
Mechanical waves
an oscill­ation of matter, and transfers energy through a material medium. ex: sound, water
formed when an electric field couples with a magnetic field. ex. light, gamma
Compre­ssion waves
the particle motion is in the same direction in which the wave is propag­ating i.e. longit­udinal
Doppler effect:
the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave
moving away= longer
Sonic boom= shock waves created when an object travels through the air faster than the speed of sound
sound barrier sudden increase in aerody­namic drag that happens when an object approaches the speed of sound

Waves pt 2: 21 questions, 17% (copy)

Snell's law:
relati­onship between angles of incidence & refraction
refraction= the bending of light or sound as it passes through something like a wall (sound) or a window (light).
reflection= the throwing back without absorbing it.
n1sin01 = n2sin02
change in direction
real image= occurs where rays converge
virtual image= rays only appear to diverge
Polari­zation= division into two sharply distinct opposites
converging= both sides of the lens curve outward it will bend light from distant objects inwards toward a single point, called the focal point
convex=refract and converge
further from lens the bigger the object appears
diverging=both sides of the lens curve inward and light from distant objects will bend outwards.
concave=refract and diverge, always smaller
+ behind lens
- in front of lens
more lenses, - the focal length

Mechanics: 44 questions, 35%

Newton's 1st
law of inertia: objects at rest remain at rest
Newton's 2nd
F=ma: the greater the mass the more force needed to accelerate
Newton's 3rd
every action has an equal and opposite reaction
Kepler's 1st
all planets move in an elliptical orbit around the sun
Kepler's 2nd
planets will move slowly far away from the sun, and faster closer to the sun
Kepler's 3rd
the square of the period of any planet is propor­tional to the cube of the axis of the orbit.
force that resists the slidin­g/r­olling of a solid object over another
Bernou­lli's principle
an increase in speed of a fluid simult­ane­ously with a decrease in pressure or a decrease in the fluid's PE
Uniform circular motion
centri­petal accele­ration, net force is directed to the center
increasing radius decreases force
Rotational motion
motion of an object around an axis. w=0/t
Harmonic motion F = -kx
Hooke's law the force exerted by a spring is propor­tional to its length
elastic- momentum conserved ex. pool balls move apart
inelastic- momentum not conserved ex. 2 cars stuck together, move together
Centri­petal force
increase radius, decrease the force. F=m(v2/r)cos0
Bouyant force F = -pgV
the upward force exerted on an object immersed in a fluid
add or subtract by placing tip to tail
Pascal's principle
The pressure at any point in the fluid is equal in all direct­ions.
pressure input = pressure output
bulk= reaction to squeezing
elastic= ratio of stress to strain
young= elasticity and length
shear= elasticity and stress
Time=2­pi(­square root (lengt­h/g­rav­ity))
freq (displ­ace­ment) = amplitude sin (ang freq * t)

Electr­icity & Magnetism: 26 questions, 21%

Coulomb's law F = k(q1q2)/r2
the force of attrac­tio­n/r­epu­lsion between 2 charged bodies is propor­tional to the product of their charges and inversely propor­tional to the square of the distance between them
allows the movement of electrons and ions through. Ex. copper, gold, silver, steel, aluminium & brass
have moveable charges
don't allow electric current to pass through, electrical resist­ance. Ex. glass, plastic, rubber, air, & wood
Ohm's law V = IR
the relati­onship between voltage, current & resistance in an electrical circuit.
Biot-S­avart law
describes the magnetic field generated by a constant electric current
Lorentz force
combin­ation of electric and magnetic force on a point charge due to electr­oma­gnetic fields. to determine the direction of the magnetic force on a positive moving charge, point right thumb in the direction of the velocity (v), index finger in the direction of the magnetic field (B), and middle finger will point in the direction of the the resulting magnetic force
Ampere's law
the sum of the length elements times the magnetic field in the direction of the length element will be equal to the permea­bility times the electric current.
Lenz's law
direction of the electric current induced in a conductor by a changing magnetic field, the magnetic field created by the induced current opposes changes in the initial magnetic field
Kirchoff's laws
sum of all currents entering a junction must equal the sum of all currents leaving the junction
Electric field
the electric force per unit charge
Electric potential V = k(q/r)
amount of work energy needed per unit of electric charge to move the charge from a reference point to a specific point in an electric field
the stronger the field= more potential
one path
Rt=R1+ R2+R3....
It= I1 =I2
Vt = V1 + V2
many paths
It = I1 + I2
Vt = V1 =V2
decrease resist­ance= decrease length, increase radius
total resistance is less than individual
Gauss's law
how much of something is INSIDE a completely closed surface by measuring how much is flowing out through the sides of that surface.
the electric flux Φ across any closed surface is propor­tional to the net electric charge q enclosed by the surface
Magnetic field
F= qvB sin 0, where q is the magnitude of the charge, B is the magnitude of the magnetic field, v is the speed, and is the angle of the velocity with respect to the field. As increases from 0° to 90°, the force increases.


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