diff --git a/src/BulletDynamics/Dynamics/btRigidBody.cpp b/src/BulletDynamics/Dynamics/btRigidBody.cpp
index 532a5c4b0..714058d5d 100644
--- a/src/BulletDynamics/Dynamics/btRigidBody.cpp
+++ b/src/BulletDynamics/Dynamics/btRigidBody.cpp
@@ -239,6 +239,9 @@ void btRigidBody::setMassProps(btScalar mass, const btVector3& inertia)
 		m_collisionFlags &= (~btCollisionObject::CF_STATIC_OBJECT);
 		m_inverseMass = btScalar(1.0) / mass;
 	}
+
+	//Fg = m * a
+	m_gravity = mass * m_gravity_acceleration;
 	
 	m_invInertiaLocal.setValue(inertia.x() != btScalar(0.0) ? btScalar(1.0) / inertia.x(): btScalar(0.0),
 				   inertia.y() != btScalar(0.0) ? btScalar(1.0) / inertia.y(): btScalar(0.0),