Physics Flashcards
Newton’s first law
-the law of inertia
-Fnet = ma = 0
-a body either at rest or in motion with constant velocity will remain that way unless a net force acts upon it
Newton’s second law
-Fnet = ma
-an object of mass m will accelerate when the vector sum of the forces results in some nonzero resultant force vector
Newton’s third law
-the law of action and reaction
FAB = -FBA
-to every action, there is always an opposed but equal reaction (for every force exerted by object A on object B, there is an equal but opposite force exerted by object B on object A)
-physical contact is not necessary for Newton’s third law
One-dimensional motion equations
v = v_0 + at
x = v0t + (a t^2)/2
v^2 = v0^2 + 2ax
x = vt (avg vel)
–when the motion is vertical, we often use y instead of x for displacement
acceleration due to gravity (g)
9.8 m/x^2
Inclined plane equations
Fg∥ = mgsinθ (gravity parallel to plane)
Fg| = mgcosθ (gravity perpendicular to plane)
Circular motion equation
Fc = mv^2/r
Torque equation
T = r x F = rFsinθ
Kinetic energy
the energy of motion, K = 1/2 mv^2 (m = mass in kg, v = speed in meters per second), the SI unit is the joule
Potential energy
energy that is associated w/ a given object’s position in space
Gravitational potential energy
depends on an object’s position with respect to some level identified as the datum (“ground” or the zero potential energy position), U = meh
Elastic potenial energy
when a spring is stretched or compressed from it equilibrium length, U = 1/2 kx^2
Work
W = F x d = Fd cosθ, SI unit is the joule
Work in an isobaric process
W = P∆V (isobaric = constant pressure)
Power
the rate at which energy is transferred from one system to another, P = W/t = ∆E/t, SI unit is the watt (J/s)
Mechanical advantage
F out/ F in
Efficiency
W out/ W in = (load)(load distance) / (effort)(effort distance), expressed as a percentage
Zeroth law of thermodynamics
when one object is in thermal equilibrium w/ another object, and the second object is in thermal equilibrium with another object, the the first and the third object are also in thermal equilibrium, when brought into thermal contact, no net heat will flow between these objects
Equations for converting between temp scales
F = 9/5C + 32
K = C + 273
where F, C, and K are the temps in Fahrenheit, Celsius, and Kelvin
Isolated systems
are not capable of exchanging energy or matter with their surroundings
Closed systems
are capable of exchanging energy, but not matter, with their surroundings
*most of systems encountered on test day will be closed
Open systems
can exchange both energy and matter with their surroundings, more energy may be transferred in the form of heat or work, examples: a boiling pot of water, human beings, and uncontained combustion reactions
First law of thermodynamics
states that the change in the total internal energy of a system is equal to the amount of energy transferred in the form of heat to system, minus the amount of energy transferred from the system in the form of work
ΔU= Q - W
Second law of thermodynamics
objects in thermal contact and not in thermal equilibrium will exchange heat energy such that the object with a higher temperature will give off heat energy to the object w/ a lower temp until both objects have the same temp at thermal equilibrium
Conversion factors between the units of heat
1 Cal = 10^3 = 4184 J = 3.97 BTU
Specific heat (c)
of a substance is defined as the amount of heat energy required to raise one gram of a substance by one degree Celsius or one unit kelvin.
Equation that relates the heat gained or lost by an object and the change in temperature of that object is
q = mcΔT
isothermal
constant temp, and therefore no change in internal energy
adiabatic
no heat exchange
isovolumetric
no change in volume, therefore no work accomplished, also called isochoric
isobaric
processes that occur at a constant pressure
Density
the ratio of mass to volume, is a scalar quantity (no direction), equation— ρ = m/V, the SI units are kg/m^3, g/mL, or g/cm^3
-*density of water is 1 g/cm^3 = 1000 kg/m^3
Equation to calculate weight of a given substance w/ a known density
Fg = ρVg
Pressure
a ratio of force per unit area, a scalar quantity, P = F/A (F= magnitude of the normal force vector, A = area), SI unit is the pascal (Pa), other common units include mmHg, torr, and atm
Conversions between Pa, mmHg, torr, and atm
1.013 x 10^5 Pa = 760 mmHg = 760 torr = 1 atm
Pascal’s Principle
for fluids that are incompressible– that is, fluids with volumes that cannot be reduced by any significant degree through application of pressure— a change in pressure will be transmitted undiminished to every portion of the fluid and onto the walls of the containing vessel
Archimedes’ Principle
deals w/ buoyancy of objects when placed in a fluid, states that a body wholly or partially immersed in a fluid will be buoyed upwards by a force equal to the weight of the fluid the it displaces
-* an object will float if its average density is less than the average density of the fluid it is immersed in, it will sink if its avg density is greater than that of the fluid
The magnitude of the current equation
I = Q/Δt
Ohm’s Law
the voltage drop between any two points in a circuit can be calculated according to this law
V = IR, measured in ohms
Resistors in a series
as electrons flow through each resistor, energy is dissipated and there is voltage drop associated w/ each resistor: Vs = V1 + V2 + V3..
the resistances of resistors in series are also additive: Rs = R1 + R2 + R3…
Resistors in parallel
electrons have a “choice” regarding which path they will take, the voltage drop experience by each division of current is the same bc all the pathways originate from a common point and end at a common point within the circuit: Vp = V1 = V2 = V3…
the equivalent resistance of resistors in parallel is calculated by: 1/Rp = 1/R1 + 1/R2 + 1/R3… (Rp decreases as more resistors are added)
Capacitors
characterized by their ability to hold charge at a particular voltage
Capacitance
the ration of the magnitude of the charge stored on one plate to the potential difference (voltage) across the capacitor
Propagation speed of a wave (v)
v = fλ
Period (of a wave) (T)
T = 1/f
Angular frequency (ω)
related to frequency, measured in radians per second, used in consideration of simple harmonic motion in springs and pendula
ω = 2πf = 2π/T
Principle of superposition
states that when waves interact w/ each other, the displacement of the resultant wave at any point is the sum of the displacements of the two interacting waves
The speed of sound
v = square root of B/ρ where B is the bulk modulus (a measure of the medium’s resistance to compression)
–the speed of sound in air at 20 degrees celsius is approximately 343 m/s
Normal range of human hearing
20 Hz to 20,000 Hz
Doppler effect
which describes the difference between the actual frequency of a sound and its perceived frequency when the source of the sound and the sound’s detector are moving relative to one other
f’ = f (v +- vD)/(v +- vS)
Intensity
I = P/A, SI unit W/m^2
the average rate of energy transfer per area across a surface that is perpendicular to the wave
Sound level (β)
β = 10 log I/I0
I0 = 1 x 10^-12 W/m^2
Wavelength
λ =2L/n
Speed of light
3.00 x 10^8 m/s
c = fλ
Converting between natural logs and common logs
log x = ln x/2.303
Estimating logarithms
log ( n x 10^m) = m + 0.n
Formulas that relate the Fahrenheit, Celsius, and Kelvin systems
F = 9/5 C + 32
K = C + 273
