How does music help drown out negativity?

One of my secrets of the gym is to blast motivational music while running or doing my abdominal exercises.  I have found that when I have to do something for a long period of time music helps me "forget" what I am doing.  By this I mean that I can focus my mind on the music, mainly the beat of the song, instead of the exercise I am performing. 

When you have no "distractions" such as music while performing an exercise that may require more repetitions, I have noticed that I will tend to not do as much.  For example, most of my abdominal exercises call for 30+ repititions.  Without music I find myself more focused on counting the reps and waiting to hit the number I have set for myself in my head.  With music, I focus less on the number and more on the beat of the song to motivate/energize my body to doing the reps.

Does it work all the time?

This depends on the person.  For me it only works for when I run or do abdominal exercises.  I find that when lifting heavy weights the music actually distracts me too much and I have a hard time focusing all my energy into the exercise I am performing.  However, there is a trick I use to drown out negativity without music when I am lifting heavy.  The trick is to let out loud grunts and all kinds of different screams J.  It is a proven fact that grunting or yelling increases your power/strength by at least 20%.  Also, if you are breathing loudly and yelling, you forget that you may be too tired to perform your 6-8 repetitions because you can't "doubt yourself" and yell at the same time; or at least I can't.

IMPORTANT: Yelling really loud in the gym is fun, it will also scare away potential people who may try to talk to you and ruin your workout!