The angular $scope is a JavaScript object which provide the connectivity between the controller and the view. All the model data bind on view (DOM element) using the $scope for a controller.
The angularjs $rootScope is the scope and one application can have only one $rootScope and It use like global variable and access in across application. The angular $rootScope is parent scope and $scopes are child scopes.
The $rootScope objects updates under a specific controller $scope not for all global controllers.
The angular $scope can't be used outside the controller and its only for current controller but the $rootScope can be used anywhere and Its available globally in the application.
All app has one-and-only $rootScope and its lifecycle is the same as the app and its all controllers can have.
The $apply and $watch are scope methods. You can see the working life-cycle in below image.
The Example in detail over $scope vs. $rootScope as given below.
<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <title>$rootScope vs $scope in AngularJs</title> <link rel="stylesheet" href="style.css" /> <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.4.6/angular.min.js"></script> <script> var app = angular.module('myApp', []); //This is Ctrl1. app.controller('Ctrl1', ["$scope", "$rootScope", function($scope, $rootScope) { $scope.scopeMsg = 'This is $scope.'; $rootScope.rootScopeMsg = 'This is $rootScope.'; }]); //This is Ctrl2. app.controller('Ctrl2', ["$scope", "$rootScope", function($scope, $rootScope) { $scope.scopeMsg = $rootScope.rootScopeMsg; }]); </script> </head> <body ng-app="myApp"> <h1>$rootScope vs $scope in AngularJs</h1> <div class="border" ng-controller="Ctrl1"> <div>Result of Ctrl1 $scope : {{scopeMsg}}</div> <div>Result of Ctrl1 $rootScope : {{rootScopeMsg}}</div> </div> <br /> <div class="border" ng-controller="Ctrl2"> <div>Result of Ctrl2 $scope : {{scopeMsg}}</div> </div> </body> </html>