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Momentum vs Impulse

  • Date Submitted: 03/04/2013 04:33 PM
  • Flesch-Kincaid Score: 53.8 
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Jacob Norton
Physics Eberlein

Impulse and Momentum
We know how to calculate the kinetic energy of moving objects -- isn't that enough? No. It turns out that many situations involving collisions do not obey the simple conservation of Mechanical Energy. Why not? Because it takes energy to bend, break, mutilate and deform objects, energy which disappears from the kinetic and gravitational potential energy. But a different quantity is conserved, even during collisions. The linear momentum of an object is defined as p=(mass) * (velocity) It is a vector quantity, and the total linear momentum of a bunch of objects will remain the same, before and after a collision. Momentum is connected to force by impulse, which is simply impulse=(force) * (time)
If the force has a constant magnitude during its action. If the force changes with time, then one must integrate to find the impulse: impulse=(force) dt. The Momentum-Impulse Theorem states that the change in momentum of an object is equal to the impulse exerted on it: (change in momentum)=(impulse) p -p=   (force) * (time) final initials m*v -   m*v =   (force) * (time) final     initial
If two cars with different masses crash head on into each other at identical speeds, the car with less mass will probably suffer more damage than the car with more mass. The car with the smaller mass is unable to withstand the impact of the car with the greater mass because the car with more mass has more momentum. Momentum is mass times velocity.  Airbags and crumple zones cannot change the impulse of an accident; however they can help protect drivers and passengers. Airbags can protect the passengers and drivers from abruptly hitting the windshield or dashboard and crumple zones protect the drivers from a high force of impact. They both also decrease the force of impact by increasing the time of impact. Force of Impact and Time of Impact are also related to braking a car. The reason why a hard slam on the brakes will be...


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