I think its supposed to be "the given action", because you cant assign a function alone to an entity. You need to assign and action, which calls functions inside of it. Below is a snippet taken from Grimber's phyisics tutorial:

Action my_car
{
//added default camera
player = my; //set me to the player
//first we let the engine know what type the physics object is
phent_settype(my,PH_RIGID,PH_box);
//next we set the mass of the object
phent_setmass(my,23,PH_box);
//we then set the friction we want
phent_setfriction(my,25);
//then we set the elasticity of the object (bounciness)
phent_setelasticity(my,50,5);
//then we set the damping
phent_setdamping(my,50,90);
//then we set our world gravity
ph_setgravity ( vector(0,0,-386) );
}

All of that is called within an action, and will be exececuted once the entity is created. Just change the function word to action:


function physFunction() {
witch = me;
phent_settype(witch, ph_rigid, ph_box);
ph_setgravity(nullvector);
phent_setmass(witch, 10, PH_BOX);
phent_setdamping (witch, 0, 0);
while(1) {
if(key_a == 1) {
phent_addcentralforce(witch, witchForceVec);
}
wait(1);
}
phent_settype(witch, 0, 0);
}


action Marmaduke_Physics_Object

{
witch = me;
phent_settype(witch, ph_rigid, ph_box);
ph_setgravity(nullvector);
phent_setmass(witch, 10, PH_BOX);
phent_setdamping (witch, 0, 0);

while(1) {
if(key_a == 1) {
phent_addcentralforce(witch, witchForceVec);
}
wait(1);
}
phent_settype(witch, 0, 0);



}