This is physics, not just maths, but the logic is interesting to all ages. Why do you need a seatbelt in a car but not on a train? The heavier mass of the tra

This is physics, not just maths, but the logic is interesting to all ages. Why do you need a seatbelt in a car but not on a train? The heavier mass of the train means the force to you is smaller, so you're less likely to get thrown as far forwards. (I just explained this to my girlfriend when she asked on the train. Thanks, engineering degree.)