Lecture 16: Collisions - Elastic and Inelastic - Center of Mass Frame of Reference
recorded by: Massachusetts Institute of Technology, MIT
published: Oct. 10, 2008, recorded: October 1999, views: 40695
released under terms of: Creative Commons Attribution Non-Commercial Share Alike (CC-BY-NC-SA)
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1. 1D Elastic Collisions:
A mass with given speed collides with a second mass (initially at rest) in a one dimensional collision. Momentum is conserved. If kinetic energy is also conserved, the velocities of both objects after the collision can be calculated. Three limiting cases are explored analytically, and then demonstrated. The equations are used to predict the outcome of some air track experiments.
2. Brain Teaser - Elastic Collision with a Wall:
A tennis ball bounces off a wall elastically. The momentum of the wall changes, but the kinetic energy of the wall remains zero. How is that possible? Something to think about!
3. Center of Mass (CM) Frame of Reference:
A 1D elastic collision is considered as seen from the CM frame of reference (where the total momentum is zero). Using the velocity of the CM in the Lab frame, you can transfer between the two frames.
4. 1D Inelastic Collision and Internal Energy:
A 1D inelastic collision is considered from the laboratory and the CM frame. The kinetic energy is calculated in both frames and it is shown that the initial KE in the CM frame is the maximum KE that can be converted to heat (this is called the internal energy of a system). The equations are used to predict the results of an air track experiment.
5. Newton's Cradle Demonstration:
Professor Lewin solicits an analytical proof of his demo showing a lineup of colliding balls.
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