Four Questions on Movies

NORTHEASTERN UNIVERSITY College of Engineering

Design Assignment #7D But I saw it in the Movies! Due Wednesday 2 November 2005

GEU 110 Fall 2005 Engineering Design Professor Freeman

Introduction

Movies have the most incredible special effects, drawing more and more people into theaters and movie rental stores to watch action and technology on screen. This seems like it would make engineering and technology very appealing. But how realistic are the things we see in motion pictures? We know that Science Fiction is not designed to be realistic, but there are many movies based around real people that seem to stretch the laws of physics. For example: the good guy shoots a bad guy who is blown backwards 10 feet by the impact of the bullet (also there is usually a large pane of glass which of course they fly through), or the car chase scene which always seem to end with one car flipping over and falling off a cliff only to explode with the force of a small nuclear device, or the exploding spacecraft that everyone on the other ship hears that is usually shot with the laser beam that everyone sees traveling through space like a torpedo or watching the hero touch a charged electric fence, bounce off and walk away. Are these amazing feats possible?

To determine whether or not Hollywood is making this stuff up usually requires the use of some simple physics. We can apply the Law of Conservation of Momentum to see how fast a person would be blown backwards if shot and actually retains the bullet. A hint to the outcome would be to think about Newton’s Third Law which states every action has an equal and opposite reaction- hence the person doing the shooting should also be blown backwards by the recoil of the gun! Have you ever seen an action hero blown back ten feet after shooting a bad guy? How about the fall through a store window? If it is our action hero, he of course emerges without a scratch. How many times have you picked up a shard of glass ever so gently but still cut yourself? To refute the exploding car scenario requires an investigation into fuel tank design and combustion principles. We all have seen pictures of horrific crashes on the news, some even involving tanker trucks filled with gas but there is rarely an explosion. The reason is for fuel to burn it must be first vaporized then mixed with the right amount of oxygen. This is not likely to happen under most circumstances, which is a good thing for those of us who have been involved in a collision. Incidentally, most car fires start in the engine compartment, not in the fuel tank. On to the question of, would we hear that spacecraft explode? The answer is no, since sound is a pressure wave that requires a medium to propagate through. Space is essentially a vacuum which means no sound. In addition, the speed of light is 3 x 108 m/s. This means that the leading and trailing ends of your laser beam are about 186,000 miles apart in one second. It is highly unlikely that our vision will ever evolve to the point of being able to see a laser beam move through space like a torpedo. If you are still NORTHEASTERN UNIVERSITY College of Engineering skeptical, try following the beam of a laser pointer to its target. So as an engineer and scientist, can you detect what is feasible and what is movie-maker Imagineering? This assignment is to test (and “showcase”) your skills in judging and analyzing an engineering principle in action. After finding an engineering feat on film, you are to dissect it, calculate it, and judge the feasibility or infeasibility of that event using math and known physical principles.

Some Simple Physics to Consider:

Conservation of Linear Momentum of Two Objects Colliding m1v1  m2v2 where m = mass (kg) and v = velocity (m/s)

Kinetic Energy 1 KE  mv 2 where m = mass (kg), v = velocity (m/s), KE = Energy (J) 2

Potential Energy

PE  mgh where m = mass (kg), g = acceleration of gravity (m/s2), h = height from a reference plane, PE = Energy (J)

Thermal Energy Transfer

Q  mcT where m = mass (kg), c = specific heat of material (J/kgK), T = temperature change (K), Q = Thermal Energy Transfer (J)

Pressure

P  F / A where F = force on an object (N), A = Area perpendicular to the direction of the force (m2), P = pressure (N/m2)

Newton’s Laws of Physics 1) Sum of Forces on an Object = 0, if the object is at rest it will stay at rest, if the object is in motion it will stay in motion 2) F  ma 3) For every action there is an equal and opposite reaction

Electrical Current Transfer

Ohm’s Law: V  iR where i = current, V = voltage (volts), R = resistance in ohms NORTHEASTERN UNIVERSITY College of Engineering

The Task

A. Form teams of three or four people. How you select a movie clip is up to you and your team. Watch the movie and document where the action is, what scene it is in, where is it located. You will need to describe that scene, and plan to show it to the class. Keep it short. Please select a scene that is tasteful; no nudity, sexual content, or explicit gore, blood, and guts.

B. Next, for your analysis of the engineering reality, use the following questions:

1. What engineering principle was captured or represented? 2. What part of that principle is correctly portrayed? 3. What part of that principle may not be correctly portrayed? 4. If the principle were corrected, what would it look like? Would it still be effective in the movie? 5. How does this example portray engineers in society (cool or not so cool)?

The written part of this assignment is brief. Answer the five questions above clearly and concisely and provide numbered diagrams and calculations with corresponding explanations for each of your points. You may include screen captures from your clip to accompany your diagrams.

C. You will prepare a 3-minute presentation in which you will show the class your film clip with the engineering example, and briefly explain how you arrived at your conclusions on the realistic or unrealistic aspects of your example. Diagrams and calculations are required. Be prepared to defend your stance.