Terrain Collider
Physics HOWTOs

Physic Material

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The Physic Material is used to adjust friction and bouncing effects of colliding objects.

Note that for historical reasons, the component is named “Physic Material” rather than “Physics Material” and the use of the unusual name is therefore intentional. The equivalent component for 2D is, however, named more logically as “Physics Material 2D”.

To create a Physic Material select Assets > Create > Physic Material from the menu bar. Then drag the Physic Material from the Project View onto a Collider in the scene.

Properties

Property: Function:
Dynamic Friction The friction used when already moving. Usually a value from 0 to 1. A value of zero feels like ice, a value of 1 will make it come to rest very quickly unless a lot of force or gravity pushes the object.
Static Friction The friction used when an object is laying still on a surface. Usually a value from 0 to 1. A value of zero feels like ice, a value of 1 will make it very hard to get the object moving.
Bounciness How bouncy is the surface? A value of 0 will not bounce. A value of 1 will bounce without any loss of energy.
Friction Combine How the friction of two colliding objects is combined.
- Average The two friction values are averaged.
- Minimum The smallest of the two values is used.
- Maximum The largest of the two values is used.
- Multiply The friction values are multiplied with each other.
Bounce Combine How the bounciness of two colliding objects is combined. It has the same modes as Friction Combine Mode

Details

Friction is the quantity which prevents surfaces from sliding off each other. This value is critical when trying to stack objects. Friction comes in two forms, dynamic and static. Static friction is used when the object is lying still. It will prevent the object from starting to move. If a large enough force is applied to the object it will start moving. At this point Dynamic Friction will come into play. Dynamic Friction will now attempt to slow down the object while in contact with another.

When two bodies are in contact, bounciness and friction modes are applied individually to each agent. So, when body A has a friction combine mode of Average and body B has mode Multiply, then A is going to behave according to average parameters and B according to multiplied parameters.

Please note that the friction model used by the Nvidia PhysX engine is tuned for performance and stability of simulation, and does not necessarily present a close approximation of real-world physics. In particular, contact surfaces which are larger than a single point (such as two boxes resting on each other) will be calculated as having two contact points, and will have friction forces twice as big as they would in real world physics. You may want to multiply your friction coefficients by 0.5 to get more realistic results in such a case.

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Physics HOWTOs