Inertia Behind The Vehicle Crash

                             The law of inertia is the basis of the new physics of the seventeenth century. This law is also true according to modern physics. Galileo discovered the law during the first decade of the seventeenth century.  Almost hundred years later Newton’s uses this idea to formulate his first law of motion.

                  

  Definition :

                    "  An object will continue to remain at rest  or  uniform motion unless acted upon by an external unbalanced force".

                   Inertia broadly classified as: 

                                           

1. Inertia of rest :

                      " The tendency of body at rest to continue to remain at rest unless an external force is applied on it".

                   we can find inertia of rest in our daily life, we can see with examples below:

Example 1:

                             

                                                       fig.1                                       fig.2

         


From fig.1 assume passenger and vehicle is in rest position.

           If suddenly vehicle moves in  forward direction, That vehicle movement pushes the passenger backward direction(fig.2).  This is due to the inertia of rest experienced by the passenger in the upper part of his body.

          The body is at rest when the bus is at rest, when the bus starts all of the sudden the lower part of the body contact with vehicle that started moving where as the upper part of the body continues to be rest because of the inertia of rest.

                                                                                                     

Example:2

                                                                        Fig.3
       
  We can  see from above picture(fig.3) glass,coin and cardboard. There is a coin on the cardboard, when the cardboard is flicked, the coin falls into the glass. This is because the inertia of coin maintains its state at rest and it falls into the glass due to gravity.

2. Inertia of direction :

                      "The tendency of the body  to oppose any changes in the  direction of its motion."


                      Example:

                      
                         If we  observe above video,  Bus is travelling on the road with passenger.  Passenger standing inside the bus with the help of grab handle. 
                       Bus is moving fast on the road, suddenly bus should cross the curved road, Than the bus negotiates right hand curve on the road the passenger will tilt to the left side . In the same manner , if the bus negotiates left hand curve on the road the passenger will tilt to the right side, This is because of " inertia of direction".

3. Inertia of motion : 

                                     "The tendency of the body  in uniform motion to continue to travel a longer straight line unless an external force  acts on it."

                         Example:

                              

                                 
                               For example  when moving car  stops all of a  sudden  than the passengers tends to move in the forward direction  this is because of  "inertia of motion".

                               From above video, assume car travelling at 50 km/hr with driver(dummy). If we observe from outside, Driver(dummy) also looks like  moving with speed of 50 km/hr. But inside the car cabin, driver don't have a motion w.r.t car before car gets impact with barrier.  Here inertia of motion acts on car and driver(dummy). 
                             In the case of car, Car moves with constant velocity(50 km/hr) unless external force either it comes from brakes or impact is  acting upon a car. 
                             If car crashes into the barrier, Front end of the car is crushing an absorbing energy which slows down the rest of the car .
                           In the case of dummy, After car gets impact with barrier, dummy keeps on moving with speed of 50 km/hr until it strikes the steering wheel  and  windshield. 
                           This is because the dummy is body in motion travelling at 50 km/hr and remains travelling 50 km/hr in the same direction until acted upon by an external force. In this case its impact with steering wheel  and windshield that applies a force  that overcomes the dummies inertia.
                           Inertia is one reason seat belts are important. If we observe above video, there is with seat belt and without seat belt crash test is going. Seat belt resists the dummy impact with steering wheel (airbag)and windshield.