Both these are examples of INERTIA. All objects have inertia. The more massive they are the more
inertia they have.
If a car stops really suddenly the people inside it
will carry on moving forwards and so be thrown forward.
You can also show the
effects of inertia by knocking away the bottom block from a pile of wooden blocks using a sharp
blow with a hammer without moving the others. The blocks have inertia and there is not enough
force on the rest of the pile to start moving.