As images and stories put us in awe of nature's destructive power, it may be worth a moment to marvel at the force of gravity that governs the behavior of all matter, from the waters of Lake Pontchartrain to light.

NPR: Defying Gravity, and Odds, in New Orleans

Bad guys are deterred by force, the threat of force, or by their cold calculation that the costs of evil behavior are not worth the risk.

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It is not surprising that a police force of 35, 000 witnessed 680, 000 instances of reasonably suspicious behavior among New York's 8.5 million residents.

WSJ: Heather Mac Donald: How to Return New York City to the Street Gangs

We have used the threat of force to try to make somebody change their behavior.

CNN: Transcript of Thursday's Democratic presidential debate

Trainees also learn the rules of engagement, laws related to use of force on airplanes and how to look out for suspicious behavior, or behavioral profiling.

CNN: STORY HIGHLIGHTS