Answer:
Inertia- the tendency of an object to resist a change in velocity
Step-by-step explanation:
Say a car was going at 65 MPH, but suddenly stopped. For all of the people in that car, their bodies would keep moving forward at 65 MPH until stopped by an equal force (say, the thing right in front of each person) The seatbelt is there to protect you from your own inertia.