308 lines
8.1 KiB
Python
308 lines
8.1 KiB
Python
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"""
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Collection of physical constants and conversion factors.
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Most constants are in SI units, so you can do
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print '10 mile per minute is', 10*mile/minute, 'm/s or', 10*mile/(minute*knot), 'knots'
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The list is not meant to be comprehensive, but just a convenient list for everyday use.
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"""
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from __future__ import division, print_function, absolute_import
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"""
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BasSw 2006
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physical constants: imported from CODATA
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unit conversion: see e.g. NIST special publication 811
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Use at own risk: double-check values before calculating your Mars orbit-insertion burn.
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Some constants exist in a few variants, which are marked with suffixes.
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The ones without any suffix should be the most common one.
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"""
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import math as _math
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from .codata import value as _cd
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import numpy as _np
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# mathematical constants
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pi = _math.pi
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golden = golden_ratio = (1 + _math.sqrt(5)) / 2
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# SI prefixes
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yotta = 1e24
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zetta = 1e21
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exa = 1e18
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peta = 1e15
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tera = 1e12
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giga = 1e9
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mega = 1e6
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kilo = 1e3
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hecto = 1e2
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deka = 1e1
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deci = 1e-1
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centi = 1e-2
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milli = 1e-3
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micro = 1e-6
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nano = 1e-9
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pico = 1e-12
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femto = 1e-15
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atto = 1e-18
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zepto = 1e-21
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# binary prefixes
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kibi = 2**10
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mebi = 2**20
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gibi = 2**30
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tebi = 2**40
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pebi = 2**50
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exbi = 2**60
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zebi = 2**70
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yobi = 2**80
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# physical constants
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c = speed_of_light = _cd('speed of light in vacuum')
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mu_0 = 4e-7*pi
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epsilon_0 = 1 / (mu_0*c*c)
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h = Planck = _cd('Planck constant')
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hbar = h / (2 * pi)
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G = gravitational_constant = _cd('Newtonian constant of gravitation')
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g = _cd('standard acceleration of gravity')
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e = elementary_charge = _cd('elementary charge')
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R = gas_constant = _cd('molar gas constant')
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alpha = fine_structure = _cd('fine-structure constant')
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N_A = Avogadro = _cd('Avogadro constant')
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k = Boltzmann = _cd('Boltzmann constant')
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sigma = Stefan_Boltzmann = _cd('Stefan-Boltzmann constant')
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Wien = _cd('Wien wavelength displacement law constant')
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Rydberg = _cd('Rydberg constant')
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# mass in kg
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gram = 1e-3
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metric_ton = 1e3
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grain = 64.79891e-6
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lb = pound = 7000 * grain # avoirdupois
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blob = slinch = pound * g / 0.0254 # lbf*s**2/in (added in 1.0.0)
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slug = blob / 12 # lbf*s**2/foot (added in 1.0.0)
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oz = ounce = pound / 16
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stone = 14 * pound
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long_ton = 2240 * pound
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short_ton = 2000 * pound
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troy_ounce = 480 * grain # only for metals / gems
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troy_pound = 12 * troy_ounce
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carat = 200e-6
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m_e = electron_mass = _cd('electron mass')
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m_p = proton_mass = _cd('proton mass')
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m_n = neutron_mass = _cd('neutron mass')
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m_u = u = atomic_mass = _cd('atomic mass constant')
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# angle in rad
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degree = pi / 180
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arcmin = arcminute = degree / 60
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arcsec = arcsecond = arcmin / 60
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# time in second
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minute = 60.0
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hour = 60 * minute
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day = 24 * hour
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week = 7 * day
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year = 365 * day
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Julian_year = 365.25 * day
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# length in meter
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inch = 0.0254
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foot = 12 * inch
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yard = 3 * foot
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mile = 1760 * yard
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mil = inch / 1000
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pt = point = inch / 72 # typography
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survey_foot = 1200.0 / 3937
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survey_mile = 5280 * survey_foot
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nautical_mile = 1852.0
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fermi = 1e-15
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angstrom = 1e-10
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micron = 1e-6
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au = astronomical_unit = 149597870700.0
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light_year = Julian_year * c
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parsec = au / arcsec
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# pressure in pascal
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atm = atmosphere = _cd('standard atmosphere')
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bar = 1e5
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torr = mmHg = atm / 760
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psi = pound * g / (inch * inch)
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# area in meter**2
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hectare = 1e4
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acre = 43560 * foot**2
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# volume in meter**3
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litre = liter = 1e-3
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gallon = gallon_US = 231 * inch**3 # US
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# pint = gallon_US / 8
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fluid_ounce = fluid_ounce_US = gallon_US / 128
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bbl = barrel = 42 * gallon_US # for oil
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gallon_imp = 4.54609e-3 # UK
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fluid_ounce_imp = gallon_imp / 160
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# speed in meter per second
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kmh = 1e3 / hour
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mph = mile / hour
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mach = speed_of_sound = 340.5 # approx value at 15 degrees in 1 atm. is this a common value?
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knot = nautical_mile / hour
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# temperature in kelvin
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zero_Celsius = 273.15
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degree_Fahrenheit = 1/1.8 # only for differences
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# energy in joule
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eV = electron_volt = elementary_charge # * 1 Volt
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calorie = calorie_th = 4.184
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calorie_IT = 4.1868
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erg = 1e-7
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Btu_th = pound * degree_Fahrenheit * calorie_th / gram
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Btu = Btu_IT = pound * degree_Fahrenheit * calorie_IT / gram
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ton_TNT = 1e9 * calorie_th
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# Wh = watt_hour
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# power in watt
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hp = horsepower = 550 * foot * pound * g
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# force in newton
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dyn = dyne = 1e-5
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lbf = pound_force = pound * g
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kgf = kilogram_force = g # * 1 kg
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# functions for conversions that are not linear
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def convert_temperature(val, old_scale, new_scale):
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"""
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Convert from a temperature scale to another one among Celsius, Kelvin,
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Fahrenheit and Rankine scales.
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Parameters
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----------
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val : array_like
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Value(s) of the temperature(s) to be converted expressed in the
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original scale.
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old_scale: str
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Specifies as a string the original scale from which the temperature
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value(s) will be converted. Supported scales are Celsius ('Celsius',
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'celsius', 'C' or 'c'), Kelvin ('Kelvin', 'kelvin', 'K', 'k'),
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Fahrenheit ('Fahrenheit', 'fahrenheit', 'F' or 'f') and Rankine
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('Rankine', 'rankine', 'R', 'r').
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new_scale: str
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Specifies as a string the new scale to which the temperature
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value(s) will be converted. Supported scales are Celsius ('Celsius',
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'celsius', 'C' or 'c'), Kelvin ('Kelvin', 'kelvin', 'K', 'k'),
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Fahrenheit ('Fahrenheit', 'fahrenheit', 'F' or 'f') and Rankine
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('Rankine', 'rankine', 'R', 'r').
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Returns
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-------
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res : float or array of floats
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Value(s) of the converted temperature(s) expressed in the new scale.
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Notes
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-----
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.. versionadded:: 0.18.0
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Examples
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--------
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>>> from scipy.constants import convert_temperature
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>>> convert_temperature(np.array([-40, 40.0]), 'Celsius', 'Kelvin')
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array([ 233.15, 313.15])
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"""
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# Convert from `old_scale` to Kelvin
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if old_scale.lower() in ['celsius', 'c']:
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tempo = _np.asanyarray(val) + zero_Celsius
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elif old_scale.lower() in ['kelvin', 'k']:
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tempo = _np.asanyarray(val)
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elif old_scale.lower() in ['fahrenheit', 'f']:
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tempo = (_np.asanyarray(val) - 32.) * 5. / 9. + zero_Celsius
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elif old_scale.lower() in ['rankine', 'r']:
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tempo = _np.asanyarray(val) * 5. / 9.
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else:
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raise NotImplementedError("%s scale is unsupported: supported scales "
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"are Celsius, Kelvin, Fahrenheit and "
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"Rankine" % old_scale)
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# and from Kelvin to `new_scale`.
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if new_scale.lower() in ['celsius', 'c']:
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res = tempo - zero_Celsius
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elif new_scale.lower() in ['kelvin', 'k']:
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res = tempo
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elif new_scale.lower() in ['fahrenheit', 'f']:
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res = (tempo - zero_Celsius) * 9. / 5. + 32.
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elif new_scale.lower() in ['rankine', 'r']:
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res = tempo * 9. / 5.
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else:
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raise NotImplementedError("'%s' scale is unsupported: supported "
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"scales are 'Celsius', 'Kelvin', "
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"'Fahrenheit' and 'Rankine'" % new_scale)
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return res
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# optics
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def lambda2nu(lambda_):
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"""
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Convert wavelength to optical frequency
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Parameters
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----------
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lambda_ : array_like
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Wavelength(s) to be converted.
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Returns
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-------
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nu : float or array of floats
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Equivalent optical frequency.
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Notes
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-----
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Computes ``nu = c / lambda`` where c = 299792458.0, i.e., the
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(vacuum) speed of light in meters/second.
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Examples
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--------
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>>> from scipy.constants import lambda2nu, speed_of_light
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>>> lambda2nu(np.array((1, speed_of_light)))
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array([ 2.99792458e+08, 1.00000000e+00])
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"""
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return _np.asanyarray(c) / lambda_
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def nu2lambda(nu):
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"""
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Convert optical frequency to wavelength.
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Parameters
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----------
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nu : array_like
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Optical frequency to be converted.
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Returns
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-------
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lambda : float or array of floats
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Equivalent wavelength(s).
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Notes
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-----
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Computes ``lambda = c / nu`` where c = 299792458.0, i.e., the
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(vacuum) speed of light in meters/second.
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Examples
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--------
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>>> from scipy.constants import nu2lambda, speed_of_light
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>>> nu2lambda(np.array((1, speed_of_light)))
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array([ 2.99792458e+08, 1.00000000e+00])
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"""
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return c / _np.asanyarray(nu)
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