Physical quantities

Physical quantities.

class sympy.physics.units.quantities.Quantity(name, abbrev=None, latex_repr=None, pretty_unicode_repr=None, pretty_ascii_repr=None, mathml_presentation_repr=None, is_prefixed=False, **assumptions)

Physical quantity: can be a unit of measure, a constant or a generic quantity.

property abbrev

Symbol representing the unit name.

Prepend the abbreviation with the prefix symbol if it is defines.

convert_to(other, unit_system='SI')

Convert the quantity to another quantity of same dimensions.

Examples

>>> from sympy.physics.units import speed_of_light, meter, second
>>> speed_of_light
speed_of_light
>>> speed_of_light.convert_to(meter/second)
299792458*meter/second

>>> from sympy.physics.units import liter
>>> liter.convert_to(meter**3)
meter**3/1000

property free_symbols

Return free symbols from quantity.

property is_prefixed

Whether or not the quantity is prefixed. Eg. \(kilogram\) is prefixed, but \(gram\) is not.

property scale_factor

Overall magnitude of the quantity as compared to the canonical units.

set_global_relative_scale_factor(scale_factor, reference_quantity)

Setting a scale factor that is valid across all unit system.

Conversion between quantities

Several methods to simplify expressions involving unit objects.

sympy.physics.units.util.convert_to(expr, target_units, unit_system='SI')

Convert expr to the same expression with all of its units and quantities represented as factors of target_units, whenever the dimension is compatible.

target_units may be a single unit/quantity, or a collection of units/quantities.

Examples

>>> from sympy.physics.units import speed_of_light, meter, gram, second, day
>>> from sympy.physics.units import mile, newton, kilogram, atomic_mass_constant
>>> from sympy.physics.units import kilometer, centimeter
>>> from sympy.physics.units import gravitational_constant, hbar
>>> from sympy.physics.units import convert_to
>>> convert_to(mile, kilometer)
25146*kilometer/15625
>>> convert_to(mile, kilometer).n()
1.609344*kilometer
>>> convert_to(speed_of_light, meter/second)
299792458*meter/second
>>> convert_to(day, second)
86400*second
>>> 3*newton
3*newton
>>> convert_to(3*newton, kilogram*meter/second**2)
3*kilogram*meter/second**2
>>> convert_to(atomic_mass_constant, gram)
1.660539060e-24*gram

Conversion to multiple units:

>>> convert_to(speed_of_light, [meter, second])
299792458*meter/second
>>> convert_to(3*newton, [centimeter, gram, second])
300000*centimeter*gram/second**2

Conversion to Planck units:

>>> convert_to(atomic_mass_constant, [gravitational_constant, speed_of_light, hbar]).n()
7.62963087839509e-20*hbar**0.5*speed_of_light**0.5/gravitational_constant**0.5