Yo could try:

var earthgravity[3] = 0,0, -386; //////////////////////////////
// -386 is the downward pulling force along the z axis
//////////////////////////////

action sphere
{

my.shadow=on;

ph_setgravity( earthgravity );//////////////////////////////
// and now you set the gravity
//////////////////////////////
phent_settype(my, PH_RIGID, PH_SPHERE);
phent_setmass(my, 5, PH_SPHERE);
phent_setfriction(my, 70);
phent_setelasticity(my, 70, 5);
phent_setdamping(my, 20, 20 );

temp.x=cos(camera.pan)*cos(camera.tilt)*300000;
temp.y=sin(camera.pan)*cos(camera.tilt)*300000;
temp.z=sin(camera.tilt)*300000;
phent_addforcelocal(my,temp,nullvector);

}

string mdl_sphere=<sphere_0.mdl>;
function emit_sphere()
{

temp.x=camera.x+cos(camera.pan)*cos(camera.tilt)*100;
temp.y=camera.y+sin(camera.pan)*cos(camera.tilt)*100;
temp.z=camera.z+sin(camera.tilt)*100;
ent_create(mdl_sphere,temp,sphere);
}
on_mouse_left=emit_sphere;