What is the difference between Discrete Events and Physics mode?

In Physics mode we pretend that the model follows the same rules of physics as applies in the real world. This means that we use physics to move the loads in the model. This also enables us to see, what happens if for instance a load falls off a conveyor, where it will then fall to the ground. In Discrete Events mode you build a route for the loads to move along. The loads will then follow the route no matter what else happens in the model, meaning that it is impossible for a load to fall off the route. In Discrete Events mode the loads only exists when they are on the route. If you start the model without finishing the route, the loads will simply disappear when they hit the end of the last conveyor/track. 

If you build a route for your loads to follow and you want a particular event to happen at a certain point in the model you have to use a sensor in Physics mode. This differs from Discrete Events mode, where you would use an action point to trigger an event. The action point and the sensor have roughly the same functionality in the two modes.

In Physics mode you have to let the model know which way the load is supposed to move through the production line whereas in Discrete Events mode you can simply instruct a load where to end up and it will find the shortest way there on its own (This is called the ‘shortest path function’).

In the grand perspective of things you can say that Discrete Events mode is a bit simpler than Physics mode. For instance two loads can not be in the same location in Discrete Events loads, whereas it is possible to have two loads next to each other in Physics mode. In Physics mode you also have the option to simulate what will happen if the product line malfunctions, this is not as easy in Discrete Events mode because the loads always follow a specific path meaning there is no room for ‘unintended’ actions to happen. However, where Physics wins on detail level, Discrete Events win on speed. Discrete Events is the only mode where you can run a model faster than real time and because the level of detail is smaller, the model will run more smoothly when you have bigger production lines.

So to sum up, in a very simplified version it comes down to speed vs. detail level, where Discrete Events can deliver on model speed and ability to handle extremely massive models while Physics mode delivers on functionality and level of detail.