according to newton first law of motion an object at rest must stay at rest, an object at motion must stay in motion. So when you are in a car driving and then you slam on the break you body moves forward towards the windshield and that because an object such as you want to be in motion because you set it on motion. Thats the same as the dummies seat belts and air bags, when a car is in a car crash it testing its seat belts and the airbags if they are fast and strong enough to stop you from going forward. Hope this helps
