tag:blogger.com,1999:blog-5088860151651047897.post2015673163773220145..comments2024-03-25T10:56:59.380-04:00Comments on Jacobs Physics: Mail time: Sorting out the work done by a springGreg Jacobshttp://www.blogger.com/profile/03854009948036330746noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-5088860151651047897.post-52258031809301373702021-02-28T18:32:39.189-05:002021-02-28T18:32:39.189-05:00Ah... everything you say is correct - no work done...Ah... everything you say is correct - no work done by external forces. No potential energy gained to compensate for kinetic energy lost.<br /><br />That's accounted for by a bar on the right-hand side for "internal energy", also known as "thermal energy". The temperature of the carts goes up in this case, because the macroscopic kinetic energy of the carts changes into sub-microscopic kinetic energies of the molecules in the carts.<br /><br />This is easier to understand if you've played squash - an indoor cross between racquetball and tennis. The ball is squishy, such that it barely bounces off the ground. Before you play, you literally must "warm up" the ball - hit it hard against the wall numerous times, each time converting the ball's kinetic energy into thermal energy, so much so that you feel the temperature difference in the warm ball.Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-8800860393595113462021-02-28T18:26:34.241-05:002021-02-28T18:26:34.241-05:00How would you approach a collision problem? Say we...How would you approach a collision problem? Say we have two carts approach each other with equal momentums, collide and stick together, stopping dead. In the system consisting of the two carts, there is some initial KE before the crash, and there's clearly zero KE in the system after the crash. But the two carts hit each other, so there was no external work done ... so how would you handle this in your bar chart?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-21681224231157711632021-02-08T16:19:37.619-05:002021-02-08T16:19:37.619-05:00It is - post is updated to reflect. Thank you for...It is - post is updated to reflect. Thank you for noticing and letting me know!Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-46377367758790729592021-02-08T15:38:18.674-05:002021-02-08T15:38:18.674-05:00Isn't the original kinetic energy 160J?Isn't the original kinetic energy 160J?Anonymoushttps://www.blogger.com/profile/05560377491001490095noreply@blogger.com