영어로 배우는 고등학교 과학 - 물리 : 탄성충돌과 비탄성충돌 [ 영문 ]

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  영어로 배우는 고등학교 과학   

  물리  -  탄성충돌과 비탄성충돌

Elastic and inelastic collisions

Although total energy is conserved, kinetic energy need not be conserved. A collision between two objects with conservation of kinetic energy is called an elastic collision. Colliding objects interacting with losses of kinetic energy due to frictional losses or deformation of an object are called inelastic collisions. In the macroscopic world, most collisions are inelastic; however, losses of kinetic energy are negligible in the nearly elastic collisions between atomic particles and subatomic particles. For these cases, the law of conservation of momentum and the conservation of kinetic energy yield useful equations.

Consider a simple head-on elastic collision where one mass ( m₁) with a given velocity ( v₁) hits a second mass ( m₂) that is initially at rest. Apply the laws of conservation of momentum and conservation of kinetic energy to get m₁ v₁ = m₁′ v₁ + m₂ v₂′ and (1/2) m₁ v₁² = (1/2) m₁ v₁′² + (1/2) m₂ v′₂², where the primes refer to velocities after the collision. Solving the equations gives the velocities of the two masses after the interaction:

Three special cases are instructive:

• For equal masses where m₁ = m₂, note that v₁′ becomes zero and v₂′ equals v₁; thus, for equal masses, the objects simply exchange velocities, as is sometimes observed with pool balls. (Pool balls have rotational energy and somewhat inelastic collisions, so their behavior only approximates the example.)

• If m₂ is massive, the numerator and denominator are nearly the same in the equation for v₁′. Then, v₁′ is approximately equal to v₁ but in the opposite direction. The denominator of the expression‎ for v₂′ will be so large so that the velocity of the second mass after the collision will be small. In other words, the incoming mass ( m₁) will bounce back off the second mass with nearly the initial speed, and the hit mass ( m₂) will move slowly after the collision.

• If m₁ is massive, then v₁′ is approximately equal to v₁, and v₂′ is nearly twice v₁; or the incoming massive particle continues at nearly the same velocity, and the hit mass moves ahead at nearly twice the initial velocity of the first mass after the collision.

Read more: http://www.cliffsnotes.com/study_guide/Work-and-Energy.topicArticleId-10453,articleId-10418.html#ixzz0jGI3as55