Impl Default for a few structs

src/geometry/broad_phase_multi_sap/broad_phase.rs

@@ -116,6 +116,12 @@ pub struct BroadPhase {
     reporting: HashMap<(u32, u32), bool>, // Workspace
 }
 
+impl Default for BroadPhase {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl BroadPhase {
     /// Create a new empty broad-phase.
     pub fn new() -> Self {

src/geometry/broad_phase_multi_sap/sap_proxy.rs

@@ -87,6 +87,12 @@ pub struct SAPProxies {
     pub first_free: SAPProxyIndex,
 }
 
+impl Default for SAPProxies {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl SAPProxies {
     pub fn new() -> Self {
         Self {

src/geometry/collider_set.rs

@@ -9,7 +9,7 @@ use crate::geometry::{ColliderChanges, ColliderHandle};
 use std::ops::{Index, IndexMut};
 
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-#[derive(Clone)]
+#[derive(Clone, Default)]
 /// A set of colliders that can be handled by a physics `World`.
 pub struct ColliderSet {
     pub(crate) colliders: Arena<Collider>,

src/geometry/interaction_graph.rs

@@ -14,6 +14,12 @@ pub struct InteractionGraph<N, E> {
     pub(crate) graph: Graph<N, E>,
 }
 
+impl<N: Copy, E> Default for InteractionGraph<N, E> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl<N: Copy, E> InteractionGraph<N, E> {
     /// Creates a new empty collection of collision objects.
     pub fn new() -> Self {

src/geometry/narrow_phase.rs

@@ -62,6 +62,12 @@ pub struct NarrowPhase {
 
 pub(crate) type ContactManifoldIndex = usize;
 
+impl Default for NarrowPhase {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl NarrowPhase {
     /// Creates a new empty narrow-phase.
     pub fn new() -> Self {