Guest Post: Bill Payne on using Audacity as a timer

Folks, Bill Payne submitted a note to the Modeling listserv that'd I'm sharing with permission as a guest post.  I always love using free software to get data that otherwise would require expensive commercial apparatus; Bill has a fantastic method of determining time intervals to millisecond precision using audacity - google "audacity" to get the free download.  Bill also provided a link to a set of follow-up questions in this excel file.  Take it away, Bill:

Bill: My kids and their teacher love shooting darts, both the kind with the suction cup end and the round end.  Last week we used the computer program Audacity to time how long it took a dart to reach a target 1 m, 2 m and 3 m away.  Audacity will give the time in milliseconds between any two sounds: the firing of a dart gun and the dart hitting the target, or you can roll a steel ball down a ramp, see where it hits the table, and place a whiteboard a measured distance from the point the ball hit the table.  Audacity is much easier to set up than photogates, and it's a free download.

Audacity will let you highlight and delete the parts of the graph you don't need, such as the flat line leading up to the firing of a dart gun.  That sets the time of the firing of the gun to zero.  Then expand the graph with Command 1 to stretch it out (repeat Command 1 to stretch it out more and more).  Cut the rest of the leader out to get the firing right on zero.  Then put your cursor on the beginning of the part of the graph when the dart hits its target, and read the elapsed time at the bottom in milliseconds.  Calculate velocity: V = d/t.

Only problem is, now the kids want to have a dart-gun war.  I put them off to the end of school.  :-)

Bill Payne

Physics Teacher

restorationacademy.org

Host of modeling workshops at Birmingham-Southern College