Cabby John 1 wrote:
Quote:
A mother or Father may strap a small child around both of them if child is sitting on their lap
I cannot remember when or where (perhaps on here);
I was told NOT to allow a parent/adult to put the strap around themselves and a child. The passenger was only allowed to strap themselves and to then hold the child outside of the strap/restraint. The reasoning was that in the event of an accident/severe braking, the inertia would snap shut firmly holding the passenger back, the passenger at the same time would also be forcibly coming forward, between the two forces it could
crush a small child sat on their lap.
V helpful - I can see this is exactly correct, from the physics :-
Scenario 1 :- child on own in seat belt. Child experiences one force F from the front ie the belt, and F = (Mass of child) x deceleration of vehicle at collision.
Scenario 2 : parent with child on lap in one seat belt together. Same deceleration occurs as before, and applies to adult AND child. NET force backwards on child is still F, as before - however that force is now composed of TWO forces ie a force F2 backwards from seat belt equal to F2 = (Mass of child + Mass of adult) x deceleration, and a force F1 coming forwards from the adult behind, equal to F1 = (Mass of adult) x deceleration.
ie F = F2 - F1
As you say these two oppositely acting forces F1 and F2 produce 'crushing' of the unfortunate child, even though they are undergoing only the same deceleration as in Scenario 1. These forces are both considerably greater than the force F in Scenario 1, as the adult is a lot heavier - so for example if adult weighs 5 times that of the child, the force from the seat belt is 6 TIMES greater than F, and at same time a 5 TIMES greater force than F is coming from behind from the adult. Nasty stuff.
(I would add that the force experienced by the adult would be the same in both cases - the only difference would be it comes from the seat belt in Scenario 1, and from the child in Scenario 2 - this force being equal to (Mass of adult) x deceleration, and there is zero force on adult from behind at the instant of collision).
(I would also say I made the above calculation assuming the deceleration of the passengers at the instant of the collision was the same in both the scenarios - which I thought would be a reasonable approximation)
Login
Register
FAQ
