Drag Force

 
 
 

This compound adds flow resistance to the movement of an object in the opposite direction to its velocity, as in a fluid. This force give a more direct level of control when you want to slow down simulated objects. For example, you could create the effect of particles moving under water using the drag force or create a slow-motion effect of particles as they are being emitted.

The drag force depends on the density or thickness of the fluid; for example, moving through air is easier than moving through water. It also depends on the velocity of the object and on its size (most importantly, the size of the object that is perpendicular to the velocity), which is why long, thin objects are aerodynamic. Drag is proportional to the square of the velocity: if you move twice as fast, the drag will be four times as strong. The degree to which the drag force slows down an object depends on its mass: heavier objects decelerate less because they have more momentum.

The drag force is opposite to an object's velocity relative to the fluid's velocity. For example, an object can't remain still in a strong current: even if its velocity is zero, its velocity relative to the current is not.

Plug this compound's Force output into a Force port on the Add Forces compound.

For more information on the using forces in ICE, see ICE Forces [ICE Guide].

Tasks: Particles/Forces

Output Ports: Force

Select Drag Type

You can control the drag's strength, as well as set the drag type to be either a simple velocity-based or a physically accurate drag:

  • Physically Accurate drag takes into account the size and mass of the particle. The Strength value needs to be smaller to achieve results that are similar to physics in real life.

  • Simple Velocity Based drag slows down the particles or objects by a ratio each frame. For example, a setting of 0.1 slows down particles or objects by 10% each frame. It generates a force that is proportional to the mass so that the particle's Mass value has no effect. You may want to use this option if you don't want to create physically accurate simulations.

Strength

Defines how much drag is applied to the particle or object each frame, which is how much velocity is lost by the object. A value of 1 stops the particle completely in one frame; a value of 0.1 means the particle loses 10% of its speed each frame.

The effect of the drag strength is different depending on the Drag Type you selected.

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