Particles Physics Model

Model Overview

This document describes the parameters for the physics model of the Particles screen saver. The model simulates the following interactions:

Attractive force (gravity) between particles.
Attractive force (gravity) between particles and the ground.
Fusion of colliding particles.
Elastic collisions with the walls of the screen.
Elastic collisions between particles.
Repulsive force between close particles.

In addition, the following features are also available:

Fading particle trails.
Explode the final particle after all particles have fused.
Show velocity and acceleration vectors.
Show the center of mass.
Change the frame rate.
Use multiple monitors together or separately.
Customizable particle colors.
Save and load the model parameter settings.

Model Parameters

Here is a description of all the options for the physics model. They can be modified using the Configuration screen in the Screen Effects Preferences.

General:

Number of Particles - The maximum number of particles in the simulation.

Particle Radius - The initial radius of each particle. (measured in pixels)

Trail Decay - The decay rate of the particle trails. A high value yields a short trail. None yields infinite trails.

Size Variance - The maximum variation in initial size of each particle. (the maximum radius is this factor times the particle radius)

Initial Velocity - The maximum possible initial velocity of each particle.

Physics:

Air Resistance - The amount of air resistance.

Wall Elasticity - The bounciness of the walls.

Particle Gravity - The strength of gravity between particles.

Overall Gravity - The strength of gravity towards the ground.

Collisions:

Fuse Particles - Combine particles when they collide. The exact condition is when the smaller particle is more than half way into the larger particle.

Explode Particles - Create an explosion after all particles have been fused.

Explode Delay - After an explosion, the delay (in seconds) before particles can interact with each other.

Explode Velocity - The maximum initial velocity of the particles after an explosion.

Elastic Collisions - Enable elastic collisions between particles.

Particle Elasticity - The bounciness of the particles in elastic collisions.

Repulsion:

Apply Particle Repulsion - Reverse the gravity between close particles.

Repulsion Multiplier - The strength of repulsion, relative to the particle gravity.

Effective Distance - The distance (in pixels) where repulsion becomes active.

Misc:

Show Vectors - Show velocity (white) and Acceleration (red) vectors.

Show Center of Mass - Show the center of mass of the system.

Show Frame Rate - Show the frame rate in the bottom left of the screen. The actual frame rate and the maximum possible frame rate are displayed.

Frame Rate - Set the frame rate of the simulation. A good value is 20.

Multiple Monitors - Select the display option for secondary monitors: blank secondary monitors, use multiple monitors together, use multiple monitors separately, and follow the main monitor.

Color:

Sample - A sample using the current color scheme. Click on it to generate a new sample.

Range of Values - The color of each particle is selected randomly within a range of possible color values.

Red - The minimum and maximum values for the red component.

Green - The minimum and maximum values for the green component.

Blue - The minimum and maximum values for the blue component.

Randomize Range of Values - Randomize the range of values after each explosion.

Specific Values - The color of each particle can take on a specific color.

Color Variance - Randomly change each color by a little bit.

Use one color at a time - Only use one of the checked colors. Cycle to the next color after an explosion.

Hints

It is possible that some parameter settings will lead to strange particle behaviors, such as jagged movement and getting stuck in the corners. This is mostly likely caused by parameters that tend to give the particles too much energy (velocity). Here are somethings to keep in mind when setting the parameters:

Adding more particles to the model will increase the effect of gravity because there is more mass in the model. This will cause the particles to travel faster, and possibly cause non-smooth movement. Lowering the gravity will counter this effect.
Unstable particle behavior can also occur when a lot of energy is given to the particles but no energy is taken away. For example, this can happen when the wall elasticity is set high and particle fusion is turned off.