You could substitute just about any action movie here. Anything starring Arnold Schwarzenegger, Sylvester Stallone, Bruce Willis, Vin Diesel, etc. should do fine. They all have the same cliches and the same bad examples of physics. The two most widely violated physical principles in movies such as “Eraser” are the Law of Conservation of Momentum and the Law of Conservation of Energy. Mind you these are two of the most immutable laws of the universe for us mere mortals, yet somehow they don’t seem to apply in Hollywood action films. (You could add the Law of Conservation of Bullets to this list, too.) One of the most egregious examples of the violiation of the Law of Conservation of Momentum comes across this way: the hero can fire away on his/her gun with practically no recoil whatsoever, yet any bad guy hit by a bullet from said gun will be violently launched off their feet and into whatever structure happens to be behind them (often a glass wall or window). It just can’t happen that way!

Assignment: Analyze in detail any of the scenes where someone fires the rail gun and hits a victim, sending them flying. Your analysis should be centered around the application of the law of conservation of momentum (which we’ll cover in class this week). This will require calculating the momentum of each of the objects involved (shooter, victim, bullet, and gun) and then appropriately applying the law of conservation of momentum. Momentum is equal to the mass of an object times its velocity, so these are the quantities you need to estimate from the movie. Keep in mind that you may need to invoke conservation of momentum more than once to fully analyze the problem. Also remember that objects can exchange momentum with other objects, provided the total momentum remains constant. If you have trouble, help each other out or ask me for more input.

You will do this week’s assignment on paper and turn it in at the start of class on Monday, 11 Sep.

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Reading assignment

pp. 49-56 – Don’t Try this at Home; Ch. 12 – ISMP

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Mission Impossible III

I’m not really interested in entering into a debate on where this particular movie ranks in the “Mission Impossible” pantheon. I do feel this one has a stronger cast of characters than I remember from the earlier ones. Ving Rhames is always fun, and Philip Seymour Hoffman is convincing as a sophisticated, yet heartless dealer of mayhem. Given the title of the franchise, I guess we can’t expect too much in the way of realistic physics (action-thrillers are usually lacking in this area anyway), yet it’s worth noting that the MI movies follow the James Bond movies in playing up the roles of high-tech gizmos and the techno-nerds behind them. It’s a cliched, yet powerful message, that the ultimate prize in “Mission Impossible III” isn’t money, gold, diamonds, or artwork, but some powerful creation of science (cleverly undisclosed, so the plot can’t go out of date with any future discovery). It is presumed to be a weapon, but we don’t even know that for sure by the end of the movie (remember, there are thriving black markets for many things other than weapons).

Anyway, it’s important to remember that we’re not to the point in the semester yet where we’re ready to judge good or bad physics (although most of you probably already know enough to make some good guesses). Before we can begin applying the laws of physics we need to learn how to make scientific observations – these will be our “experiments.” To make a useful observation, you first need to decide what to observe. Not everything happening in the world around you or in a movie scene is relevant to the questions you are trying to answer at the time. For instance, if you’re trying to figure out if a person really can basejump off a building, it’s not terribly relevant what city the building is in or what time of day it is. More relevant are how tall the building is and how quickly the person can get their chute deployed. Once you’ve filtered the relevant from the irrelevant information, you can set about the task of actually making your measurements. In movie scenes, this isn’t always easy. You can’t pull out a measuring stick or put the object in question on a scale. You may need to step through scenes one frame at a time so you can carefully analyze the images. You may need to estimate unknown lengths in scenes by using objects of known size that are also in the scene to set the scale. You may occasionally need to resort to outside resources to help you. For instance, in our example, you may need to go online to look up how tall the building in question is or how long a basejump chute needs to be deployed to sufficiently slow a jumper’s descent. Finally, you may have to make some educated guesses.

Assignment: This week I want you to analyze at least 3 scenes from the movie “Mission Impossible III.” I want you to: 1) state what physical question you are trying to answer in each scene; 2) state what the relevant quantities are you would need to measure to answer your posed questions; and 3) give me your best estimates for those quantities and some explanation of how you came up with your estimates. To make things more consistent for me, I would like everyone to use the scene of agent Ethan Hunt (Tom Cruise) swinging from one building to another in Shanghai as one of the scenes you analyze. Other scenes you might consider are the helicopter chase scenes, the drone aircraft attack on the bridge, or agent Hunt’s base jump from the building in Shanghai. Or choose some of your own scenes. In making your estimates, you can use whatever units you like (whatever is convenient for you, just don’t forget to include units). For instance, you might use the common American unit of a foot for measuring length. However, I also want you to convert your measurements into metric units (meters, kilograms, seconds, etc.) There are a variety of tools available on the web to help you do this. REMEMBER, the point of this assignment is NOT to measure every possible quantity in a scene, it’s to measure the relevant quantities. So at least half of the task on this assignment is judging what’s relevant. And you can only do that AFTER you’ve decided what question you’re trying to answer.

Please post your answers to your blog by Sunday, 3 Sep.

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Reading Assignment

Ch. 1 – Don’t Try this at Home, Ch. 1 – ISMP

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I will provide you with a copy of the syllabus for this course on the first day of class, but if you ever want to find it online, it is available at

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Welcome to FYSE 130 – “Physics in Film!” This is my sixth time teaching this course and it seems like it’s more fun every time! I’m looking forward to meeting the new students this week and having some fun discussions about physics and movies!

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