Instance Property

density

The relative mass density of the behavior’s dynamic items.

Declaration

@property(readwrite, nonatomic) CGFloat density;

Discussion

A dynamic item’s relative density, along with its size, determines its effective mass when it participates in UIKit Dynamics behaviors—including friction, collisions, pushes, and so on. For example, say you have two dynamic items with the same density but different sizes: item one is 100 x 100 points and item two is 100 x 200 points. In this example, item two has twice the effective mass of item one. In an elastic collision, these items exhibit a natural conservation of momentum according to their relative masses.

A 100 x 100 point dynamic item with a density of 1.0, to which you apply a force (via a push behavior) of magnitude 1.0, accelerates at 100 points per second².

See Also

Configuring a Dynamic Item Behavior

- addAngularVelocity:forItem:

Adds a specified angular velocity to a dynamic item.

- addLinearVelocity:forItem:

Adds a specified linear velocity to a dynamic item.

allowsRotation

Specifies whether rotation is allowed for the behavior’s dynamic items.

angularResistance

The angular resistance for the behavior’s dynamic items.

- angularVelocityForItem:

Returns the angular velocity for a specified dynamic item.

- linearVelocityForItem:

Returns the linear velocity for a specified dynamic item.

elasticity

The amount of elasticity applied to collisions for the behavior’s dynamic items.

friction

The linear resistance for the behavior’s dynamic items when two slide against each other.

resistance

The linear resistance for the behavior’s dynamic items, which reduces their linear velocity over time.

charge

The charge associated with the item.

anchored

A Boolean value indicating whether the item is anchored to its current position.