Firebase $remove() confused about using ref.key() or $id - firebase

Question

I am building a very simple edit/delete function for a list of posts and got the update function working with:
$scope.update = function() {
var fb = new Firebase("https://mydb.firebaseio.com/Posts/" + $scope.postToUpdate.$id);
var article = $firebaseObject(fb);
article.Title = $scope.postToUpdate.Title;
article.Intro = $scope.postToUpdate.Intro;
article.Body = $scope.postToUpdate.Body;
article.$save().then(function(ref) {
console.log($scope.postToUpdate.Title);
}, function(error) {
console.log("Error:", error);
});
}
I assumed that the delete function would be almost identical i.e.
$scope.deletePost = function() {
var fb = new Firebase("https://mydb.firebaseio.com/Posts/" + $scope.postToDelete.$id);
var article = $firebaseObject(fb);
$scope.postToDelete = article;
article.$remove().then(function(ref) {
console.log("removed:" + $scope.postToDelete.Title);
}, function(error) {
console.log("Error:", error);
});
}
button: <button type="button" ng-click="deletePost()">Delete</button>
But nothing happens. I tried the verion with the firebase ref_key instead but this still has not worked
$scope.deletePost = function() {
var fb = new Firebase("https://mydb.firebaseio.com/Posts/" + id);
var id = ref.key();
var article = $firebaseObject(fb);
$scope.postToDelete = article;
article.$remove.then(function(ref) {
console.log("removed:" + $scope.postToDelete.Title);
}, function(error) {
console.log("Error:", error);
});
}
I have been reading through some of the threads and wondering if article should be an array in order to delete the entire object? How do I target the specific item in order to delete it?
FIXED WITH: article.$remove(article).then(function(ref) But I still do not understand when to use ref.key() or $id (firebase/angularfire?)