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It wouldn't be summer without a Jerry Bruckheimer blockbuster, and Memorial Day weekend brought the first of 2010 with Prince of Persia: The Sands of Time. This movie is based on a video game, following in the footsteps of Super Mario Brothers, Mortal Kombat, and Lara Croft: Tomb Raider. (I wonder when Pong: Duel on the Court will be produced.) Although most students are on summer break now, science teachers can build an archive of summer movies to spark discussions when classes resume in the fall.
The titular Prince of Persia here is Dastan, a poor boy adopted by the Persian king, who has two biological sons, Garsiv and Tus. Dastan (Jake Gyllenhaal) will never inherit the throne, but he is loved by the king, who respects his bravery and innovation on the battlefield. Acting on the advice of the King's brother, Nizam, the three brothers lead an assault on the holy city of Alamut. Dastan's high-risk attack on a side gate leads to the assault's success, and Dastan takes a beautiful, mysterious dagger from a palace guard. Afterward, the king objects to the attack, because of Alamut's sacred status, but appears placated when Dastan presents a captured prayer robe as a gift. Unfortunately, the robe is poisoned, and Dastan is suspected of killing the king. He barely escapes from the city with Princess Tamina and the dagger, discovering by accident that the dagger has the power to turn back time, if only for a minute. The rest of the plot follows Dastan's search for his father's killer, taking him through a number of unlikely twists and turns. I'm not going to discuss time travel or the magical elements in the film; instead I'll make some suggestions for physics teachers who want to connect motion and energy to students' summer entertainment.
Dastan spends a great deal time trying to get into or out of tight spots, and being chased by large numbers of enemies. He uses every available bar, ledge, stairway, rooftop, rope, and basket to his advantage. Most of the stunts look very much like parkour, a relatively new sport that began in France in the late 20th century. The point of parkour—sometimes called free running—is to use a gymnast's strength and balance to move quickly through an urban environment. An enthusiast might avoid time-consuming stairs by jumping from the second floor of a structure to the ground. Or he might climb over a wall instead of bothering with a gate or door. Why waste time going down to the ground floor to cross the street when you can jump from one rooftop to the next? Needless to say, the potential for injury is very great, but experienced free runners use solid physics principles to protect themselves.
To avoid injury when landing from a great height, you need to absorb the impact over the greatest time possible, and/or transfer straight-line motion into rotational motion. Athletes do this by landing with knees bent, so the flexing of their legs slows their body over a longer time interval than if they landed with legs straight. If the landing is particularly hard, it can help to land and roll forward, rather than trying to stop. The roll transfers a great deal of kinetic energy from translation (getting from one place to another) into rotation (the spinning of the body.) You can see a young Dastan using this trick in the trailer for Prince of Persia available here. I use a similar technique when rollerblading. The brakes on rollerblades are too small to help me stop quickly, and it isn't possible to use the ‘hockey stop' done on ice. Instead, I use the brake to slow down a bit, and then spin in a circle to stop.
Screen shot from Prince of Persia: The Sands of Time.
Another one of Dastan's spectacular feats is featured prominently in the above trailer. He gracefully dives off from the top of a wooden frame above Alamut, holding a rope. He then turns in the air to swing feet first into the palace to surprise his attackers. (Bruce Willis used the same tactic in the first Die Hard movie using a fire hose.) It's a neat trick, and physics students could make some quick estimates of Dastan's decrease in gravitational potential energy as he falls, and therefore his increase in kinetic energy. From this, his speed can be estimated, if you make a guess at his mass. I am also impressed by his ability to get the length of the rope just right to swing in the window, rather than crash into the wall a half-meter too high or too low—without the benefit of careful measurements!
While I don't see many Academy Award nominations in the offing for Prince of Persia, it's a good start to the summer movie season, and physics teachers can make use of Dastan's feats of urban gymnastics to kick off discussions of energy in September.
Jacob Clark Blickenstaff is Assistant Professor of Physics and Assistant Director of the Center for Science and Mathematics Education at the University of Southern Mississippi. He can be reached at email@example.com.
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