Physics Review Flashcards
Formula for Work
W=FcosTHETAd
F=force (kg*m/s^2)
d=distance (m)
Inertia
The ability of an object to resist a change to its velocity
Formula for Center of Mass
Cmass = (r1m1 + r2m2 + r3m3 . . . )/mtotal
r=radius or (displacement vector between reference point and each mass)
Where is center of gravity located?
Exactly at the center of mass
Center of bouyancy
located exactly at the center of mass of the fluid displaced by the submerged
object (NOT at the center of mass of the submerged object itself).
Newton’s first law
An object that is in motion will stay in motion unless acted on by a force. An object at rest will stay at rest “”. Law of inertia
Constant force
A constant net force will always cause a constant acceleration—and therefore a changing velocity.
**A force is not needed to keep an object moving.
Displacement
The shortest distance between point A and point B.
Velocity and Speed
On the MCAT, you can treat “speed” the same as “velocity” if (and only if) the question makes it clear
that the distance traveled is along a straight line.
Constant velocity or constant speed =
1) No acceleration
2) No net force
3) All forces sum to zero (i.e., up forces = down forces, left forces = right forces, etc.)
4) No change in direction
5) The object is in equilibrium
Velocity Formula
V=Delta X/ Delta T
Velocity changes ____ m/s while airborn
10m/s
Average velocity
Vavg = (V1 + V2)/2.
Distance formula
Rate (average velocity) * Time
m/sec sec
EX: V=3m/s T=3s D=9m
Formula for Range
Vx * T
Vx=velocity in x direction T=time
Thoughts for projectile motion
1) Horizontal velocity never changes (as long as you are ignoring air resistance)
2) Horizontal acceleration always = 0
3) Vertical acceleration always = 10 m/s2 downward
4) Vertical behavior is exactly symmetrical (i.e., if ignoring air resistance, a projectile’s upward
trip is identical to its downward trip)
5) Time in the air depends on the vertical component of velocity only
6) Range depends on both the vertical and horizontal components of velocity
7) Time is always the same for both the x and y components of the motion.
Three formulas to know:
X(distance)= (½)at2, Velocity= √(2gh) or Velocity= √(2ax), tair= 2V/g
factors affect the magnitude of air resistance:
1) Cross-sectional Area: greater cross-sectional area = more air resistance
2) Shape: less aerodynamic = more air resistance
3) Velocity: increased velocity = more air resistance.
At terminal velocity:
mg=Fair
Universal Law of Gravitation:
F=Gm1m2/r^2
G=6.67e10^-11 Nm^2/kg^2 (gravitational constant, does not change)
Simplified: F=mg
Formula for potential energy:
PE=mgh
If dealing with a fluid, replace mass with density
PE = ρgh
Formula for Density;
ρ=mass/volume
ρ=density
Formula for potential energy in space:
PE = -Gm1m2/r
Formula for gravity:
g = Gm/r2
Force on an incline plane:
Parallel: F = mgsinθ
Perpendicular: FN = mgcosθ This is =Fn (normal force)
Velocity at bottom of inclined plane:
V = √(2gh)
Hooke’s Law
F = k∆x
k=spring constant
x=displacement of spring from it’s equilibrium position
– the force (F) needed to extend or compress a spring by some distance X scales linearly with respect to that distance.
Elastic Potential Energy: The potential energy
stored in a compressed spring (or in any other
object that follows Hooke’s Law)
PE = (1/2)k∆x2
Simple Harmonic Motion (SHM)
Anything that oscillates back and forth, and can be represented by a sine
wave graphically, constitutes Simple Harmonic Motion.
Formulas for period in spring and pendulum systems
T = 2pi√(m/k) [mass on a spring]
o T = 2pi√(L/g) [pendulum]
Specific gravity:
A ratio that describes how dense something is compared to water.
SG = Dsubstance/DH2O
- For any object floating in any liquid, the ratio of SGobject to SGliquid will exactly equal the
fraction of the object submerged in the liquid.
Buoyancy force:
Fbuoyant = ρvg
v=volume of the fluid displaced not volume of object
- the buoyant force is always exactly equal to the
weight of the amount of fluid displaced by the object
General Pressure Formula:
P=F/A units: pascals, mmHg, atm
Guage pressure:
Absolute pressure is this plus atmospheric pressure
measured with respect to atmospheric pressure, where atmospheric pressure is
defined as zero gauge pressure. Put another way, gauge pressure is the amount of pressure in
excess of the ambient atmospheric pressure.
Fluid pressure formula
P = ρgh
Pascal’s Law:
Pressure is transmitted in all directions, undiminished, through a contained,
incompressible fluid.
Flow Rate:
Q = AV
Bernoulli’s Equation
K = P + ρgh + (½)ρv^2
Increase in fluid flow = decrease in pressure
Surface tension:
The intensity of intermolecular forces, per unit length, at the surface of a liquid
Apparent weight:
Apparent Weight (AW) = Actual Weight (aW) – Buoyant Force (Fbuoyant)
What type of wave is light?
Transverse,
What type of wave is sound?
Longitudinal
Energy of a photon:
E=hf h: plancks constant f: frequency
Young’s slit experiment:
x = lamda*L/d ; where x is the distance between fringes,lamda is the wavelength of light used, d is the
distance between the two slits, and L is the distance between the “double slit” and the final screen.
The law of conservation of energy:
Energy in an isolated system is always conserved.
Formula for work:
W = ∆Energy
Machines relationship with work:
Machines never reduce or change the amount of work!
Power formula:
1) P = ∆E/t
2) P = W/t
Charge of an electron:
e- = 1.6 x 10-19C
How are magnetic fields created?
Magnetic fields are created by changing electric field.
Magnetic fields are also created by currents (moving charges)
Current flow: I = ∆q/∆t
Current flows opposite to the direction of electron flow.
Current moves from positive (+) to negative (-)
Electrons flow from negative (-) to positive (+)
Ohm’s law formula:
V = IR
Capacitance formula:
C = Q/V
PE stored by a capacitor:
U = ½CV2
Resistors in series:
Resistors in series: add the resistance of each resistor directly
▪ Rtotal = R1 + R2 + R3…
Resistors in parallel:
1/Rtotal = 1/R1 + 1/R2 + 1/R3…
Capacitors in series:
1/Ctotal = 1/C1 + 1/C2 + 1/C3…
Capacitors in parallel:
Ctotal = C1 + C2 + C3…
Batteries in series:
▪ Vtotal = V1 + V2 + V3…
Kirchoff’s rules:
▪ Kirchoff’s 1st Rule: total current into a node = total current out of a node
▪ Kirchoff’s 2nd Rule: in any closed loop circuit, the sum of the voltages equals zero (i.e., the sum of the voltage drops across each resistor equals the total voltage of the battery)
Electromagnetic waves:
No medium required; capable of propagating in a vacuum; transfer energy and momentum through space (e.g., visible light, microwaves, radio waves, etc.)
Mechanical waves:
Require a medium to propagate; cannot propagate in a vacuum; transfer energy in the direction of propagation, but do not transfer matter. (sound waves, waves on a string)
Wave speed formula:
V = λf
The 3 cardinal wave rules:
1) Wave speed (velocity) is determined by the medium
2) Frequency never changes when a wave moves from medium to medium
3) Wavelength does change when a wave moves from medium to medium
Diffraction:
. Diffraction is the tendency of light to
spread out as it goes around a corner or through a slit.
Frequency of light sources: (inverse to wavelength)
In terms of frequency, gamma rays > x-rays > ultraviolet > visible light > infrared > microwaves >
radio waves
Frequency of light sources: (inverse to wavelength)
In terms of frequency, gamma rays > x-rays > ultraviolet > visible light > infrared > microwaves >
radio waves
Speed of light in a vacuum?
All of the waves on the electromagnetic spectrum travel at the same speed in a vacuum, the
speed of light.
Color spectrum wavelengths:
ROY G BIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet) 700nm———————-> 300nm violet
Index of refraction formula;
n = c/v
A value of 1.5 for n simply tells us that the medium has some density, and is more dense than air, which has a value for n that is very close to one.
When going from low density to high, it will turn towards the right, or the middle line. Vis versa
Effect on frequency and wavelength in medium change:
Frequency is constant, if going from low to high medium then wavelength would have to increase to compensate .
Total internal reflection:
For light crossing a boundary from a slower to a faster medium (like from glass or water into air), if the angle of refraction would be 90° or more, the incident light does
not enter the second medium at all—100% of the light is reflected off the boundary and back into the first medium. For total internal reflection to occur, the light must be passing from a higher-index medium to a lower-index medium.
Diffraction:
is the bending of a wave around a corner or obstacle.
Dispersion:
is a change in index of refraction based on the frequency (or wavelength) of a wave. In a material with dispersion, different frequencies (or wavelengths) will be refracted to different angles, for the same
incident angle
2 image types:
o Virtual: There is no actual light emanating from or reaching the image (e.g., the image formed behind a plane mirror)
o Real: There is actual light at the image (e.g., an image formed on your retina)
Converging lenses:
Converging (a.k.a., convex, positive) = usually produces a positive, real, inverted image.
When the object is inside the focal point it produces a negative, virtual, upright image.
Diverging lenses:
Diverging (a.k.a., concave, negative) = always produces a negative, virtual, upright image.
Mirror formula:
f = ½r
Nearsightedness or Myopia:
is the inability of the eye to focus on distant objects. Results from bulging cornea or elongated eyeball. This tends to cause the images of distant objects to form at locations in front of the retina. The cure for the nearsighted eye is to equip it with a diverging lens. This will cause light to diverge before reaching the eye then converge to correct location on cornea.
Farsightedness or Hyperopia:
is the inability of the eye to focus on nearby objects. The problem most frequently arises during latter stages in life, as a result of the weakening of the ciliary muscles and/or the decreased flexibility of the lens. the images of nearby objects are focused at a location behind the retina. farsighted eye is assisted by the use of a converging lens.
Thin lens and thin mirror equation:
1/f = 1/di + 1/do do= object distance di=image distance
Magnification formula:
M = -di/do = hi/ho If M (magnification) is negative, means the image is inverted.
Four lens/ mirror rules:
1) Object distances (do) are ALWAYS (+)
2) Image distances (di) or focal point distances (f) are (+) if they are on the same side as the observer, and (-) if they are on the opposite side from the observer.
3) The observer and the object are on the same side for a mirror, and on opposite sides for a lens (You have to be behind your glasses to see through them!)
4) PRI / NVU: “Positive, Real, Inverted” and “Negative, Virtual, Upright” These two trios of image descriptors always stick together. As long as you can confidently establish that the image has one of those three characteristics, you automatically know the other two!
Ciliary muscles contract=
shortening, thickening of lens, used to see images close up. As the curvature of a lens increases, its focal point decreases
Ciliary muscle relax=
elongating, relaxing of lens, used to see images far away
Formula for relationship between power and focal point:
P=1/f
Distance , velocity, time , acceleration equation
X=1/2at^2
