<story><title>Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery</title><url>http://www.planetary.org/blogs/guest-blogs/2014/0419-forensic-ballistics.html</url></story><parent_chain></parent_chain><comment><author>tc_</author><text>The article&amp;#x27;s discussion of golf balls reads completely opposite to standard well-accepted theory.  The author writes:&lt;p&gt;&amp;gt; &lt;i&gt;[The &amp;quot;drag catastrophe&amp;quot;] is when an object is falling so fast that the boundary layer of gas separates off the object and the drag force suddenly drops by a factor of almost 10. The reason why golf balls have dimples is to cause this drag catastrophe to happen at slightly slower speeds, so the ball will travel a lot farther.&lt;/i&gt;&lt;p&gt;This is very confused.  Golf balls have dimples to &lt;i&gt;prevent&lt;/i&gt; flow separation.  The dimples are turbulators meant to induce turbulent flow around the golf ball before the laminar flow would otherwise give way to flow separation.  Far from decreasing the drag force, flow separation increases it substantially.&lt;p&gt;[Also, the term &amp;quot;drag catastrophe&amp;quot; appears to have no relevant hits on Google other than this one article.]&lt;p&gt;[Edit 1]: The author is well qualified and unlikely to be confused himself; so I don&amp;#x27;t doubt his conclusion.  Reading charitably, turbulent flow might be called a form of separated flow, and this must be what the author means.  His coefficient of drag graph supports this interpretation as his &amp;quot;drag catastrophe&amp;quot; would be happening when you would expect a transition flow (from separated laminar to turbulent).  Pedagogically he should have more clearly distinguished it from the typical laminar separated flow.</text></comment>
<story><title>Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery</title><url>http://www.planetary.org/blogs/guest-blogs/2014/0419-forensic-ballistics.html</url></story><parent_chain></parent_chain><comment><author>mixmax</author><text>Submissions like this is the reason I frequent HN! A thorough well written and well researched article that point by point dissects an interesting event and comes to a surprising conclusion.&lt;p&gt;If you come across other articles of this calibre please submit them!</text></comment>