Parameters: Units

Model ElementParam_Unit defines the units for the model being defined.

Description

Param_Unit allows you to specify four types of units: Mass, Length, Time, and Force. The last is obviously a function of the first three and can be automatically calculated for a consistent set of units. However, many unit systems are not "consistent", so it may be necessary to specify a force unit also.

The table below summarizes the key units types supported in MotionSolve.
Mass Units Length Units Force Units Time Units
Gram Inch Ounce_Force Millisecond
Milligram Foot Pound_Force Second
Kilogram Mile Kpound_Force Minute
Megagram Millimeter Dyne Hour
Pound_Mass Centimeter Newton Microsecond
Slug Meter Kilogram_Force Nanosecond
Ounce_Mass Kilometer KNewton Day
Kpound_Mass Nanometer CentiNewton  
Tonne Angstorm MilliNewton  
Microgram Yard MicroNewton  
Nanogram MilliInch MegaNewton  
US Ton MicroInch Poundal  
Slinch Mils NanoNewton  
  Micrometer    

Format

<Param_Unit
   {     mass_mult_factor    = "real"     
     | [ force_unit          = "name" ]       
       [ mass_unit           = "name" ]       
       [ length_unit         = "name" ]       
       [ time_unit           = "name" ] >
   }
</Param_Unit>

Attributes

mass_mult_factor
Defines the multiplication factor to be used so that Newton's second law, Force = Mass * Acceleration, is still valid for the set of units used by the user. mass_mult_factor has a default value of 1.0.
force_unit
Defines the units for force. Select from:
  • Ounce_Force
  • Pound_Force
  • Kpound_Force
  • Dyne
  • Newton
  • Kilogram_Force
  • KNewton
  • CentiNewton
  • MilliNewton
  • MicroNewton
  • MegaNewton
  • Poundal
  • NanoNewton
mass_unit
Defines units for mass. Select from:
  • Gram
  • Milligram
  • Kilogram
  • Megagram
  • Pound_Mass
  • Slug
  • Ounce_Mass
  • Kpound_Mass
  • Tonne
  • Microgram
  • Nanogram
  • US_Ton
  • Slinch
length_unit
Defines the units for length. Select from:
  • Inch
  • Foot
  • Mile
  • Millimeter
  • Centimeter
  • Meter
  • Kilometer
  • Nanometer
  • Angstrom
  • Yard
  • MilliInch
  • MicroInch
  • Mils
  • Micrometer
time_unit
Defines the time units. Select from:
  • Millisecond
  • Second
  • Minute
  • Hour
  • Microsecond
  • Nanosecond
  • Day

Example

Defining an SI units system:

<Param_Unit
     force_unit          = "NEWTON"
     mass_unit           = "KILOGRAM"
     length_unit         = "METER"
     time_unit           = "SECOND" >
</Param_Unit>
For a user defined units system, assume the set of units you are working on is as follows:
  • Mass is specified in grams.

    The mass scale is 10-3 Kg.

  • Length is specified in micrometers.

    The length scale is 10-6 m.

  • Time is specified in milliseconds.

    The time scale is 10-3 s.

  • Force is specified in Newtons.

    The force scale is 1 N.

A mass multiplication factor is defined as follows:

mass_mult_factor = mass_scale * length_scale/(force_scale * time_scale*time_scale)
= 10-3 * 10-6 / (1 * (10-3)2)
= 10-9 / 10-6
= 10-3

The Param_Unit blocks is as follows:

<Param_Unit
   mass_mult_factor = "0.001"
</Param_Unit>
Below is the definition of Param_Unit for the following set of units:
  • Mass in Kilograms
  • Length in millimeters
  • Time in seconds
  • Force in Newtons
<Param_Unit
     force_unit          = "NEWTON"
     mass_unit           = "KILOGRAM"
     length_unit         = "MILLIMETER"
     time_unit           = "SECOND" >
</Param_Unit>

The example below shows the definition of the British units.

<Param_Unit
     force_unit          = "POUNDFORCE"
     mass_unit           = "POUNDMASS"
     length_unit         = "FOOT"
     time_unit           = "SECOND" >
</Param_Unit>

Comments

User units are defined using the mass_mult_factor keyword.