If Quinton is standing on a train that suddenly moves forward, what happens to the cup of coffee he is holding?

Provide a very short response.
When the train suddenly moves forward, Quinton's body and the cup of coffee he is holding will try to remain in their current state of rest due to inertia. This will cause the coffee to spill towards Quinton, as his hand and the cup lag behind while the train accelerates forward underneath them.