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# PhysicalProperties

PhysicalProperties is an object that describes several physical properties of a part: Density, Elasticity and Friction. It is used in the similarly-named `BasePart/CustomPhysicalProperties` property.

## Weighting Behavior

PhysicalProperties also provides weightings properties, ElasticityWeight and FrictionWeight. When two parts interact, the Friction and Elasticity between them are determined in the same way by the following pairwise weighted average function: Although the formula above refers to the Friction and FrictionWeight of two parts, A and B, the formula is used in the same manner when determining Elasticity. Generally, when the weight of A is much greater than that of B, the actual value will be closer to A. If the weights are similar, then the actual value will be close to the midpoint between their individual values.

## History

PhysicalProperties was released in November 2015. Previously, BasePart had individual Friction and Elasticity properties. This was changed so that all physical properties of a part will replicate as one, among other reasons. Its release was done over the course of three months.

## Constructors

 PhysicalProperties.new ( Enum material ) Creates a PhysicalProperties container, with the density, friction, and elasticity specified for this Material.
 PhysicalProperties.new ( number density, number friction, number elasticity ) Creates a PhysicalProperties container, with the specified density, friction, and elasticity.
 PhysicalProperties.new ( number density, number friction, number elasticity, number frictionWeight, number elasticityWeight ) Creates a PhysicalProperties container, with the specified density, friction, and elasticity, as well as the weight of the friction and elasticity.

## Properties

 number PhysicalProperties.Density The density set for the custom physical properties. Density is defined as the amount of mass per unit volume. The more dense a part is, the more force it takes to accelerate it.
 number PhysicalProperties.Friction The friction set for the custom physical properties. Friction is defined as the force that opposes the relative lateral motion of two solid surfaces in contact. The greater the friction on a part, the quicker it will decelerate when it rubs against another part with friction.
 number PhysicalProperties.Elasticity The elasticity set for the custom physical properties. On Roblox, Elasticity refers to a part’s tendency to retain energy when colliding with another part. An Elasticity of 1 indicates that the part bounces with the same energy it had before a collision.
 number PhysicalProperties.FrictionWeight The friction weight set for the custom physical properties. The FrictionWeight of two parts rubbing together creates a ratio used to calculate the actual friction between the two parts: the higher a part’s FrictionWeight is, the more its Friction will be used.
 number PhysicalProperties.ElasticityWeight The elasticity weight set for the custom physical properties. The ElasticityWeight of two parts colliding creates a ratio used to calculate the actual elasticity between the two parts: the higher a part’s ElasticityWeight is, the more its Elasticity will be used.