# Like a buf­falo, horse or gi­raffe hit­ting your car

Weekend Argus (Sunday Edition) - - NEWS -

TO un­der­stand the brute force of rocks fall­ing on cars, the fol­low­ing ve­loc­ity and im­pacts were es­ti­mated and com­pared.

DATA:

Bridge height: 5m

Speed of car: 120km/h Weight of rocks: can vary sig­nif­i­cantly, any­thing from 3kg to 20kg seems rea­son­able.

Ad­di­tional data also in­volved in equa­tion.

Data is as­sumed un­der gen­eral cir­cum­stances and the pro­jec­tile be­ing dropped and not thrown.

A 3kg rock dropped from a 5m high bridge on a car trav­el­ling at 120km/h is equal to the im­pact of a 183kg weight dropped from a height of 1m, which is equiv­a­lent to the weight of a small pi­ano.

A 9kg rock dropped from a 5m bridge would im­pact a car with the same amount of en­ergy as a 549kg mass be­ing dropped from 1m.

This is roughly the weight of a buf­falo.

A 15kg rock dropped from a 5m bridge would im­pact a car with the same amount of en­ergy as a 549kg mass be­ing dropped from 1m. This is roughly the weight of a horse.

A 20kg rock dropped un­der the same con­di­tions is equiv­a­lent to drop­ping 1 219kg from 1m. This is ap­prox­i­mately the weight of a gi­raffe.

En­ergy val­ues for dif­fer­ent rock masses

Mass of rock = Equiv­a­lent mass dropped from 1m height

3kg = 183 kg

5kg = 305kg

7kg = 427kg

9kg = 548kg

11kg = 670kg

12kg = 731kg

15kg = 914 kg

20kg = 1219kg

Data sup­plied by Shamik Ma­haraj, a mas­ters quantum physics stu­dent at the Uni­ver­sity of KwaZu­luNatal.