Forces Simulator

The simulator started with a wooden figure pushing objects.(Sleepy dog, crate, text book, fridge, file cabinet, and mystery item) There was the file cabinet which to move over a surface with friction, needed to be at least 246 net force in either direction.  When the forces are unbalanced it starts moving. However, after the force has been applied then no more is applied, the filing cabnet will stop moving due to friction and its weight. After the filing cabnet simulator, there is a robot moving company. You move another filing cabnet, a textbook and a sleepy dog. You only have a certain amount of energy to move one object. You cant push it too hard or your robot will run out of energy or it will fly off a cliff. Sometimes both. You have the unbalanced force of the robot, and then after friction and the weight of the object it will stop outside the door of a house. Sometimes, you push the object too hard and then have to stop it before it goes off the cliff, thus balancing the forces. Here is the simulator:http://phet.colorado.edu/en/simulation/forces-and-motion and here is another link helping explaining balanced and n balanced forces: http://www.physicsclassroom.com/class/newtlaws/u2l1d.cfm