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Illustration 8.6: Microscopic View of a Collision

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In the animation, a red 80-kg ball with an initial kinetic energy of 360 J is trapped inside a box with rigid walls containing a cylinder constructed of 80 small 1-kg spheres (position is given in meters, time is given in seconds, and energy shown on the bar graph is given in joules). The ball crashes into the cylinder and breaks it apart. The bar graph displays the kinetic energy of the red ball. The table displays the time, momentum, and kinetic energy of the red ball. Restart.

This animation is meant to simulate a collision between two solid objects, one of which is stationary. The stationary object is a loose collection of smaller objects and approximates a larger solid object. This is only an approximation since this object should stay together, not break apart. When you do collision experiments in the lab the objects colliding do not usually deform this much! Nevertheless, we can learn a lot from this animation. As the red ball hits the blue object, the blue object deforms, absorbing some of the red ball's kinetic energy and momentum. If the blue object were indeed solid, the deformed object—the entire object—would move to the right. We can imagine this by considering the average motion of the small blue balls that make up the larger solid object. We note that the general motion of these blue balls is to the right. Where does all of the initial kinetic energy go? It goes into the kinetic energy of the small blue balls.

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