Module moog.physics.friction

Friction forces.

This file has two classes, KineticFriction and Drag. The only difference between the two is that kinetic friction is velocity-independent, whereas drag scales linearly with velocity. For joystick control of agents, using Drag is a bit easier since it prevents the velocity from exploding.

Expand source code 
"""Friction forces.

This file has two classes, KineticFriction and Drag. The only difference between
the two is that kinetic friction is velocity-independent, whereas drag scales
linearly with velocity. For joystick control of agents, using Drag is a bit
easier since it prevents the velocity from exploding.
"""

from . import abstract_force
import numpy as np


class KineticFriction(abstract_force.AbstractNewtonianForce):
    """Kinetic friction force class."""

    def __init__(self, coeff_friction=1.):
        """Constructor.

        Args:
            coeff_friction: Scalar. Coefficient of friction. The frictional
                force applied to a sprite is -coeff_friction * sprite.mass.
        """
        self._coeff_friction = coeff_friction

    def _compute_forces(self, sprite):
        velocity_norm = np.linalg.norm(sprite.velocity)
        if velocity_norm == 0:
            normalized_velocity = np.zeros(2)
        else:
            normalized_velocity = sprite.velocity / velocity_norm
        force = -1 * self._coeff_friction * normalized_velocity * sprite.mass

        return (force,)
        

class Drag(abstract_force.AbstractNewtonianForce):
    """Drag force class.
    
    Note: The drag force implemented here depends only on {velocity, mass,
    coef_friction}, not on cross sectional area, so it is not a realistic drag
    force.
    """

    def __init__(self, coeff_friction=1.):
        """Constructor.

        Args:
            coeff_friction: Scalar. Coefficient of friction. The frictional
                force applied to a sprite is
                -coeff_friction * sprite.velocity * sprite.mass.
        """
        self._coeff_friction = coeff_friction

    def _compute_forces(self, sprite):
        force = -1 * self._coeff_friction * sprite.velocity * sprite.mass
        return (force,)

Classes

class Drag (coeff_friction=1.0)

Drag force class.

Note: The drag force implemented here depends only on {velocity, mass, coef_friction}, not on cross sectional area, so it is not a realistic drag force.

Constructor.

Args

coeff_friction
Scalar. Coefficient of friction. The frictional force applied to a sprite is -coeff_friction * sprite.velocity * sprite.mass.
Expand source code 
class Drag(abstract_force.AbstractNewtonianForce):
    """Drag force class.
    
    Note: The drag force implemented here depends only on {velocity, mass,
    coef_friction}, not on cross sectional area, so it is not a realistic drag
    force.
    """

    def __init__(self, coeff_friction=1.):
        """Constructor.

        Args:
            coeff_friction: Scalar. Coefficient of friction. The frictional
                force applied to a sprite is
                -coeff_friction * sprite.velocity * sprite.mass.
        """
        self._coeff_friction = coeff_friction

    def _compute_forces(self, sprite):
        force = -1 * self._coeff_friction * sprite.velocity * sprite.mass
        return (force,)

Ancestors

Inherited members

class KineticFriction (coeff_friction=1.0)

Kinetic friction force class.

Constructor.

Args

coeff_friction
Scalar. Coefficient of friction. The frictional force applied to a sprite is -coeff_friction * sprite.mass.
Expand source code 
class KineticFriction(abstract_force.AbstractNewtonianForce):
    """Kinetic friction force class."""

    def __init__(self, coeff_friction=1.):
        """Constructor.

        Args:
            coeff_friction: Scalar. Coefficient of friction. The frictional
                force applied to a sprite is -coeff_friction * sprite.mass.
        """
        self._coeff_friction = coeff_friction

    def _compute_forces(self, sprite):
        velocity_norm = np.linalg.norm(sprite.velocity)
        if velocity_norm == 0:
            normalized_velocity = np.zeros(2)
        else:
            normalized_velocity = sprite.velocity / velocity_norm
        force = -1 * self._coeff_friction * normalized_velocity * sprite.mass

        return (force,)

Ancestors

Inherited members