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Unformatted text preview: Module 9: Elastic and inelastic Collision A collision is an isolated event in which two or more bodies (the colliding bodies) exert relatively strong forces on each other for a relatively short period of time. In all collisions, momentum is conserved. Energy, as the sum of all its forms, is also conserved every time. These two principlesconservation of momentum and conservation of energyhold true at all levels: at the grand scale of stars and galaxies, in everyday situations such as collisions between balls on a billiard table, through to the atomic interactions between the particles that make up matter. Although total energy is conserved in a collision, it is unusual for any one form of energy to be conserved. Collisions can be (i) elastic, or (ii) Totally inelastic. (i) Elastic Collision : An elastic collision is one in which both the kinetic energy and momentum of the system are conserved. Energy changes during collisions: In an elastic collision, the total kinetic energy of the system before the collision is equal to the total kinetic energy of the system after the collision. However, the kinetic energy of the system is not necessarily constant at all times throughout the collision. Consider an almost elastic collision between two air track gliders, A and B, fitted with spring bumpers as shown in Fig.2. Before the collision, glider A carries the total kinetic energy of the system. When the gliders are in contact, glider A slows down and glider B begins to move. The total kinetic energy of the gliders has actually decreased during this time because some of the kinetic energy is momentarily stored in the springs. When the spring bumpers return to their original length, this elastic potential energy is transformed back into kinetic energy as the gliders move apart. After the contact, the total kinetic energy of the gliders is equal to the initial kinetic energy of the system. Figure 2 During this elastic collision, the total kinetic energy of the system decreases when the gliders are in contact. At this time, some energy is stored as elastic potential energy in the spring bumpers, and then transformed back into kinetic energy. The total kinetic energy before the collision is approximately equal to the total kinetic energy after the collision. 1 Before During After Figure 1: A flowchart showing the system in which a collision occurs . These energy changes are shown graphically in Fig. 3. In an elastic collision, the total mechanical energy (i.e. kinetic and potential energy) remains constant at all times. During the contact between the bodies, some energy is stored as potential energy and the total kinetic energy of the bodies is reduced. However, this potential energy is all returned as kinetic energy. The total kinetic energy before the collision is equal to the total kinetic energy after the collision....
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- Spring '11