Forces

Forces are one of the fundamental processes in Mechanica that cause objects to move. We provide a suite of pre-built forces, and users can create their own.

The forces module collects all of the built-in forces that Mechanica provides. This module contains a variety of functions that all generate a force object.

mechanica.forces.berendsen_thermostat(tau)

Creates a Berendsen thermostat

Param:tau: time constant that determines how rapidly the thermostat effects the system.

The thermostat picks up the target temperature \(T_0\) from the object that it gets bound to. For example, if we bind a temperature to a particle type, then it uses the

The Berendsen thermostat effectively re-scales the velocities of an object in order to make the temperature of that family of objects match a specified temperature.

The Berendsen thermostat force \(\mathbf{F}_{temp}\) has a function form of:

\[\mathbf{F}_{temp} = \frac{\mathbf{p}_i}{\tau_T} \left(\frac{T_0}{T} - 1 \right),\]

where \(T\) is the measured temperature of a family of particles, \(T_0\) is the control temperature, and \(\tau_T\) is the coupling constant. The coupling constant is a measure of the time scale on which the thermostat operates, and has units of time. Smaller values of \(\tau_T\) result in a faster acting thermostat, and larger values result in a slower acting thermostat.

..class:: ConstantForce(value, period=None)

A Constant Force that acts on objects, is a way to specify things like gravity, external pressure, etc…

param value:value can be either a callable that returns a length-3 vector, or a length-3 vector. If value is a vector, than we simply use that vector value as the constant force. If value is callable, then the runtime calls that callable every period to get a new value. If it’s a callable, then it must return somethign convertible to a length-3 array. param period:If value is a callable, then period defines how frequenly the runtime should call that to obtain a new force value.