org.gicentre.utils.network.traer.physics
Class Spring

java.lang.Object
  org.gicentre.utils.network.traer.physics.AbstractForce
      org.gicentre.utils.network.traer.physics.TargetedForce
          org.gicentre.utils.network.traer.physics.TwoBodyForce
              org.gicentre.utils.network.traer.physics.Spring

All Implemented Interfaces:

Force

public class Spring
extends TwoBodyForce

Class for representing a physical spring by extending TwoBodyForce to calculate the force with a spring constant (ks), damping factor (d), and an ideal length (l). Thus, the positions of the Particles on either end obey the equation:
ddot(r) = -k/m * (r-l) - d/m * dot(r)

Since:

4.0

Author:

Jeffrey Traer Bernstein, Carl Pearson and minor modifications by Jo Wood.

Nested Class Summary

Nested classes/interfaces inherited from class org.gicentre.utils.network.traer.physics.TwoBodyForce

TwoBodyForce.ForcePair

Constructor Summary

Spring(Particle oneEnd, Particle theOtherEnd, float ks, float d, float l)
Creates a spring with the given properties between the given particles.

Method Summary

float	currentLength() Gets the current Spring length; uses the end particle positions to do so.
float	damping() Reports the damping constant of the spring d; Will always be greater than 0.
TwoBodyForce.ForcePair	forcePair() Calculates the spring forces on each of the particles at either end of the spring.
float	restLength() Reports the ideal length, l; always more than 0.
Spring	setDamping(float d) Sets the damping constant of the spring d.
Spring	setRestLength(float l) Sets the ideal length of the spring.
Spring	setStrength(float ks) Sets the strength of the spring ks; must be greater than 0.
float	strength() Reports the strength of the spring ks; always more than 0.

Methods inherited from class org.gicentre.utils.network.traer.physics.TwoBodyForce

apply, equalAndOpposite, getOneEnd, getTheOtherEnd, setOneEnd, setTheOtherEnd, specifyBoth, turnOff, turnOn, turnOn

Methods inherited from class org.gicentre.utils.network.traer.physics.TargetedForce

apply

Methods inherited from class org.gicentre.utils.network.traer.physics.AbstractForce

isOff, isOn

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Spring

public Spring(Particle oneEnd,
              Particle theOtherEnd,
              float ks,
              float d,
              float l)
       throws java.lang.NullPointerException,
              java.lang.IllegalArgumentException

Creates a spring with the given properties between the given particles.

Parameters:

oneEnd - the one end Particle; cannot be null

theOtherEnd - the other end Particle; cannot be null

ks - the spring constant.

d - the damping constant.

l - the ideal length of the spring.

Throws:

java.lang.NullPointerException - if either Particle is null, via TwoBodyForce.TwoBodyForce(Particle, Particle)

java.lang.IllegalArgumentException - if l is not positive, via setRestLength(float).

java.lang.IllegalArgumentException - if ks not positive, via setStrength(float).

java.lang.IllegalArgumentException - if d less than 0, via setDamping(float).

Method Detail

currentLength

public final float currentLength()

Gets the current Spring length; uses the end particle positions to do so.

Returns:

the current Spring length

restLength

public final float restLength()

Reports the ideal length, l; always more than 0.

Returns:

the ideal length of the spring.

setRestLength

public final Spring setRestLength(float l)
                           throws java.lang.IllegalArgumentException

Sets the ideal length of the spring.

Parameters:

l - the new rest length; must be positive.

Returns:

This spring with its new rest length.

Throws:

java.lang.IllegalArgumentException - if rest length is negative

strength

public final float strength()

Reports the strength of the spring ks; always more than 0.

Returns:

ks, the spring constant

setStrength

public final Spring setStrength(float ks)
                         throws java.lang.IllegalArgumentException

Sets the strength of the spring ks; must be greater than 0.

Parameters:

ks - the new spring constant; must be greater than 0.

Returns:

This spring with its new strength.

Throws:

java.lang.IllegalArgumentException - if ks is not positive.

damping

public final float damping()

Reports the damping constant of the spring d; Will always be greater than 0.

Returns:

d, the damping constant.

setDamping

public final Spring setDamping(float d)
                        throws java.lang.IllegalArgumentException

Sets the damping constant of the spring d.

Parameters:

d - the new damping constant. Must not be negative but can be 0 for no damping.

Returns:

This spring with its new damping constant.

Throws:

java.lang.IllegalArgumentException - if d is negative.

forcePair

public TwoBodyForce.ForcePair forcePair()

Calculates the spring forces on each of the particles at either end of the spring.

Specified by:

forcePair in class TwoBodyForce

Returns:

the spring forces at each end of the spring.