Unit A Conclusion
1. Unit A Conclusion
Unit A Conclusion
In Module 1 you explored the concepts of momentum and impulse as they relate to the function and design requirements of vehicle safety devices. In this context, you discovered that momentum is the product of the mass and velocity of an object and that it is a vector quantity. The direction of the momentum vector is the same as the direction of the velocity vector.
You then applied Newton’s second law to explain that the external, non-zero, net force acting on an object will be equal to the rate of change of the momentum of that object. This has particular relevance to situations involving large changes in momentum, such as those of vehicle collisions that occur at a high rate of speed. This relationship helps makes sense of the phrase “speed kills.” The faster an object is going, the greater the momentum that object has—and the greater the potential for more serious collisions.
From this, you learned that impulse is the change in momentum, 
, and is the product of net force and time. Understanding impulse helps you understand how we can attempt to reduce injury and death in vehicle collisions where the occupants experience a large change in momentum. The force associated with a given impulse can be reduced by applying it over a greater time period, a principle related to the design of vehicle safety devices such as air bags and crumple zones.
In Module 2 you explored collisions in an isolated system and gained an understanding of the law of conservation of momentum, which states that the sum of the momentum in a system before a collision equals the sum of the momentum in the same system after a collision. Expressed as an equation, it is as follows:
You also learned that there are two different types of collisions and that we can analyze elastic and inelastic collisions to determine initial velocities or predict final velocities or mass of the objects by applying the conservation of momentum principle. You first analyzed this in linear collisions and then applied that knowledge to analyze non-linear collisions in two dimensions, such as two cars meeting in an intersection. You discovered that momentum is still conserved in a two-dimensional collision. Specifically, the total momentum in the x direction and in the y direction is also conserved during a collision.
Therefore, 
and 
.
Lastly, you investigated the total kinetic energy of a system before and after a collision and discovered that kinetic energy is not always conserved. Furthermore, the amount of lost kinetic energy can be used to produce a spectrum of elasticity:
- Perfectly elastic collisions result in the total kinetic energy of the system being conserved. Perfectly elastic collisions generally occur only at the subatomic level.
- Inelastic collisions involve some loss of kinetic energy, generally as sound or thermal energy. This is a broad range, and most collisions fall within this class.
- Perfectly inelastic collisions are ones in which the colliding objects stick together upon impact. There is the greatest loss of kinetic energy in this type of collision.
Throughout this unit, you have learned how to explain how momentum is conserved when objects interact in an isolated system.