Show that $Ns = Kg \: m/s$ OR Ns = $Kg \: ms^{-1}$

Difficulty: Easy

L.H.S = Ns = $(1 kg \: \times 1 \: ms^{-2}) \times s = kg \: \times ms ^{-2+1}= kg \:\times ms ^{-1} =kg \: ms^{-1}$



Fragile objects such as glassware etc. are packed with suitable materials such as Styrofoam rings, balls, polythene sheets with air sacks, etc.

The air enclosed in the cavities of these materials makes them flexible and soft. During any mishap, they increase the impact time on fragile objects. An increase in impact time lowers the rate of change of momentum and hence lessens the impact of force. This lowers the possible damage due to an accident.



In an accident at high speed, the impact force is very large due to the extremely short stopping time. For safety purposes, vehicles have rigid cages for passengers with crumple zones at their front and rear ends.

 During an accident, crumple zones collapse. This increases the impact time by providing extra time for crumpling. The impact of force is highly reduced and saves passengers from severe injuries.



In case of an accident, a person not wearing a seatbelt will continue moving until stopped suddenly by something before him. This something may be a windscreen, another passenger, or the back of the seat in front of him/her. Seatbelts are useful in two ways:

  • They provide an external force to a person wearing a seatbelt.
  • The additional time is required for stretching seat belts. This prolongs the stopping time for momentum to change and reduces the effect of a collision.