How do seat belts relate to newtons second law of motion?

Answer 1

Newton's 2nd law is F=ma. That is Force is equal to mass times acceleration. The use of a seat belt prevents acceleration of the restrained person. This reduces the effects of the crash.

If we look at this in detail, a person is riding in a car that is travelling 25 miles an hour on a road. The person weighs 200 lbs. The things that are considered here are the speed of the car and it needs to be converted to FPS which is Feet Per Second. 25 MPH is 37 FPS. Since force equals mass times acceleration. IF that car hits a parked car then the person that is described in this scenario is going to move forward with a force of 7400 ft lbs. Depending on what the persons body hits inside the car, that amount of force can do tremendous damage and cause death. A seatbelt that is being worn stops the acceleration from taking place and distributes the force over the surface area of the straps where they are in contact with the body. That is why seatbelts must be worn correctly. There are other considerations in this scenario. The seatbelt has a little slack in it. There are things like pretension devices that take the slack out. Airbags now are installed to try and reduce forces. Cars are made to crush and reduce the forces. Another consideration is that the organs in the persons body are subjected to these forces. So the brain, liver, heart, gall bladder, spleen etc also accelerate and strike the inside of the body and become damaged.