1. Science in the Movies: The Science Behind Stunts & Special Effects
Hot Science - Cool Talk # 34
Science in the Movies: The Science Behind Stunts & Special Effects
Steve Wolf
February 4, 2005
Produced by and for Hot Science - Cool Talks by the Environmental Science Institute. We request that the use of these materials include an acknowledgement of the presenter and Hot Science - Cool Talks by the Environmental Science Institute at UT Austin. We hope you find these materials educational and enjoyable.

2. SIM Logo

3. Stunt & Special Effects Coordinator
Steve Wolf
Stunt & Special Effects Coordinator
I’m Steve Wolf, and I have to most exciting job in the world. I set up stunts and special effects for movies and television shows. That means that it’s my job to crash cars, blow up buildings, set people on fire and work with movie stars.

4. Science & Safety
I do all this using basic science that I learned in elementary and middle school. What I’m going to do in this presentation is to show you some of the ways that I use the science that I learned years ago to set up movie stunts and special effects.

5. Stay away from drugs and alcohol
Movie Star Tips!
Get plenty of sleep
Eat healthful foods
Exercise regularly
Stay away from drugs and alcohol
Stay away from cigarettes and cigarette smoke
Several years ago, I got to work on a movie called “The Firm” with Tom Cruise. I was sitting on the special effects truck and I started thinking about how much money Tom Cruise was making. I figured out that he was making over $100, every day that he came to work (and that was several years ago!). Now if you could make $100, every day you came to work I’m sure you wouldn’t want a miss very many days of work. Imagine, in one day, Tom earns what it takes teachers months and months to earn. And if the star of a movie is unable to work for a day, then neither can the crew of hundreds of people… so missing work for a star is a very, very expensive problem. I was curious to know how Tom Cruise and other movie stars made sure that they don’t ever miss work, so I studied their habits, and I noted some important things.

6. Three States Of Matter Solids Liquids Gases
Because we want to keep actors (and ourselves) away from real smoke we use smoke machines that creates fake smoke that is safe to inhale and to be around. Making “smoke” relies on the principle that there are three states of matter, and works simply by changing a substance from one state to another. Matter is anything in the universe that can be touched, and while it occasionally comes in some unusual forms like plasma, the vast majority of matter exists in one of three states. Much the way ice cream pretty much comes in chocolate, vanilla and strawberry, the matter that makes up the universe is usually found as a solid, a liquid, or a gas.
Solids are materials that hold their own shape. The molecules in a solid stay close to each other and don’t move around. Liquids usually stay together but the molecules are free to move around each other. In a gas, the molecules fly around freely and will spread out as far from each other as they can.

7. LIQUID
Liquid + Heat
HEAT
GAS
One of the things that’s really neat about solids, liquids and gases is that very often the same material can exist in all three states depending simply upon how much energy is in it. So you can take a solid, like an ice cube, which holds its own shape, and just by adding heat to it, you can turn it into liquid water. If you take that liquid, that we call water, and you add heat to it, you can turn it into a gas. That gas is what we call steam or water vapor.
You can change a substance from one state to another by adding or removing heat.

8. Animation of liquid to gas
We can create “smoke” by adding heat to a liquid to create a gas, and that’s the way a smoke machine works. It takes a harmless liquid, and adds heat to it to turn it into a gas. When you take the liquid, and you turn it into a gas, you’d be amazed at how much the liquid expands. In fact, just four drops of smoke-making liquid, with its closely packed molecules, when turned into a gas, will form enough gas to fill a room with fake smoke. The “smoke” created with the smoke machine looks very real in the movie, but it’s harmless to be around.

9. Read Labels!
Whenever you work with any material always read the labels to make sure you are aware of any potential dangers.

10. Components of Fire: Fuel Oxygen Heat Chemical Reaction
Now I’m sure you’ve heard an expression about smoke that says, “Where there’s smoke, there’s… Fire!”. I have to make fire and lots of times in movies. And to make fire you have to have the right ingredients. So, just as if I were baking a cake I would need butter, flour, sugar and eggs, when I’m making a fire I also have to have the right ingredients. To make fire you have to have fuel, oxygen, heat and a chemical reaction. When you bring together fuel, oxygen, heat and a chemical reaction you get… fire! Fuel is what we’re going to burn. Oxygen is a gas in the air around us that we need in order to live. Heat excites the molecules of the fuel and the oxygen bringing them together so that are ready to react with each other. And the chemical reaction allows the fuel and the oxygen to combine chemically and make new products.

11. Chemical Reaction Chemical Reaction
In a chemical reaction the atoms that make up a substance are rearranged to make new substances. The original ingredients are called the reactants and the resulting components are called the products of the reaction.

12. Fluids take the shape of the container you put them in
Two out of the three states of matter are fluids, (that is liquids and gases). Fluids are materials that take the shape of the container in which they are placed. If you pour water into a glass, it takes the shape of the glass, so it’s a fluid. If you blow air into a balloon, the air takes the shape of the balloon, so it’s a fluid. No matter what you put a brick into, it still retains the shape of a brick, so it’s not a fluid, it’s a solid.
For the fuel that’s actually burning when we do fire stunts, we use a fuel called propane. If you’ve ever seen a television show called “King of the Hill” then you’ve probably heard about propane and propane accessories. The fuel that we use, the propane, is stored in metal containers. Incidentally, most of the propane in the tank is in the form of a liquid, which evaporates into a gas as we use it.
A valve is used to control the flow of propane gas. A valve is a simple mechanical device that controls the flow of a fluid. While you might think of valves as devices for scientists, an ordinary bathroom or kitchen faucet is a valve, so if you brushed your teeth this morning, you’re already used a valve today. Depending on how much fuel I add to a fire, by opening and closing valves, I can make the fire bigger or smaller and control it.

13. Life on Earth is based on!
CARBON
A common product of the reaction that creates fire is carbon. Have you heard of fuels being called hydrocarbons? That means that the elements that make this fuel are hydrogen and carbon. And when we chemically combine them with oxygen, and rearrange the molecules through the process of burning, we’re making new things, like carbon. Carbon is a good thing. You know where you could find lots of carbon? Look in the mirror. Every cell in your body is made using carbon molecules. Twenty percent of your body weight is carbon. In fact, everything living thing on this planet is made using carbon molecules. It’s in people, dogs, cats, lettuce and tomatoes and even teachers. Since it’s in every living thing, scientists call life on Earth “carbon based life.”

14. If there is a fire in the house
GET OUT!
When things burn, some of the carbon molecules in the fuel join with oxygen molecules from the air around us to make a poison gas called carbon monoxide. In a fire, enormous amounts of carbon monoxide are created, and it can kill you. Carbon monoxide has no smell so you don’t know when it’s around you unless you have a carbon monoxide detector in your home. Gases can spread very quickly, so it’s extremely important to remember that if there’s ever a fire in your home you need to get out of the house IMMEDIATELY, and then call 911.
The reason carbon monoxide is so poisonous, is because it forms very strong attachments to the hemoglobin in our blood, which carries oxygen. But when a carbon monoxide molecule attaches itself to hemoglobin molecule, there’s no place for the oxygen, so if you breathe carbon monoxide, you suffocate from the inside. People who have been exposed to high levels of carbon monoxide usually turn bright red, so if you find someone passed out and bright red it could be a warning that you’re in an area with dangerous levels of carbon monoxide.

15. If there is a fire in the house
GET OUT!

16. Dial 9 1 1
Dial 911 on the telephone in the case of an emergency, such as a fire.

17. Gravity
GRAVITY
When stunt people jump off buildings the work of getting them to the ground is furnished courtesy of gravity. A stunt person does not have to jump any harder to fall from a tall building as from a short building.
Many people think that falling is dangerous. I’ve never seen anyone injured while falling. I have however seen people killed by landing - it’s important to distinguish between proximate and contributing causes. Landing is the dangerous part, but as long as you’re falling your safe. In fact, we have a saying in the stunt business, “it’s not the fall that kills you, it’s the sudden stop at the bottom.”

18. Humpty Dumpty
Image from:

19. Animation of person landing in airbag
We want to make sure that whenever a stunt person is falling they always have a nice soft landing. And the way we make sure that stunt people always have a nice soft landing is by giving them something soft to land on. We do that is using a device called an airbag, which is like a giant marshmallow mattress that’s filled with air, and when you land on it, it goes squishhhhhhhhh... and slows down your landing so you don’t splat like an egg on the sidewalk.

20. Gases are Compressable
Landing on an airbag is like landing on a big spring. Gases can be compressed because there is a great deal of space between the molecules of gas.

21. “Things should be made as simple as possible, but not any simpler
“Things should be made as simple as possible, but not any simpler.” -Albert Einstein
So, we’ve got gravity doing all the work of getting the stunt person from the top of the building down to the ground, and we’ve got an air bag to slowly absorb the energy of the falling stunt person and give them a nice safe landing.
There’s just one thing left to figure out --getting them back up to do it again. Because unlike a daredevil act, where the performer might get hurt, a stunt person is a professional who has to be able to perform the same stunt over and over again without getting hurt. We’re not trying to create danger, we are instead safely using science to create the illusion of danger.
So, how we get our stunt performer back up to the top of the roof? Well, for filming in a skyscraper downtown, all we have to do to get the stunt person back up to the top of the building is put them in the elevator and press the button. Helicopters are also an options, but an elevator is much simpler.
Image:

22. Basic tools that make work easier
Simple Machines
Basic tools that make work easier
Sometimes elevators are not available. If we’re filming at the edge of a cliff or at the top of a crevasse and there is no elevator, we have to have another way to get our stunt person back up to the top. We have to know how to use simple machines to accomplish certain tasks.

23. The Six Simple Machines!
Levers
Ramps
Wheels & Axels
Screws
Wedges
There are six simple machines - levers, ramps, screws, wedges, wheels and axles, and my favorite, pulleys. Basically, simple machines are devices that multiply your strength. They let you get really hard things done by breaking the task up over time or distance, so that ends up being very easy.
Complicated machines are just a combination of the basic six simple machines.
Pulleys

24. Pulley
A wheel with a rope around it.
A pulley simply changes the direction and force of a rope. A series of pulleys can multiply your effort allowing you to lift things that are heavier than you. The effort is multiplied by the number of rope sections supporting the load.
I first read about pulleys when I was in the fourth grade, and I learned that by using pulleys you could effectively multiply your strength to let you lift things that were heavier than you. Now, I was a pretty small kid in the fourth grade, so the idea of being able to lift things that were heavier than I was sounded pretty cool. I was so excited about pulleys that I got an after school job so that I could make some money to buy myself some pulleys, some rope and a harness. I’ll never forget the day that I came home from the store with my pulleys. I set them up in a big oak tree in my backyard. I attached half of them to a big branch about 20 feet up in the air, and the other half were down on the ground attached to a harness. Then I ran into my house to look for something heavier than I was that I could try to lift. And the first thing I came across was… my mom! I told my mom that I had learned about pulleys in school and that I had bought a bunch of them and I asked her to come outside and let me see if they really worked. Well, she looked at my like I was nuts, but then she said, “Yes!” --she came outside, and she stepped into the harness, and I started pulling on the rope, and she started going up, and she was screaming, and I was laughing, and I lifted her about 20 feet in the air! It was so exciting, and I had so much fun, that I’ve been lifting people with pulleys ever since.
A pulley is just a wheel with an axle running through it that changes the direction and movement of a rope. If I have a rope running through one pulley, and I pull down on one side of the rope, the other side of the rope goes up. If I pull down on one side with about 10 lbs. of force, the other side goes up with about 10 lbs. of force. So one pulley doesn’t really multiply your strength, it just changes the direction of the force that the rope can apply. In fact, pullies multiply your strength by the number of pulleys that you use. So if you have a rig that uses nine pulleys, it can multiply your strength nine times. When we’re using machines to multiply our strength, or allow us to lift or move things easily that would normally be difficult or impossible for us to move, we call the benefit “mechanical advantage.” If a simple machine or collection of simply machines multiplies the force that you apply by, say, nine times, then we would say that it has a mechanical advantage of nine to one. You never really get a hundred percent of the benefits in real life that you get on paper, because of friction and other lost effort, but it gets you pretty close.
Effort is multiplied by the number of rope sections supporting the load.

25. Always Wear Your SEAT BELT!
The harnesses stunt people wear are made of the same materials as seatbelts. Always wear your seatbelt.

26. Tensile Strength
A property of matter that measures how much you can pull something before it breaks.
Seatbelts and harnesses are effective because they have very high tensile strength. Tensile strength is a property of matter.

27. When materials rub together they create and friction creates HEAT
If a rope slides through your hand you get a rope burn. This happens because when materials rub together they create friction and friction creates heat. Heat can create burns.

28. Pressure and Force
When lots of air molecules are forced into a fixed space the pressure created within the space increases. This pressure can be used to do work, like blowing things up.

29. Pressure A force acting against a surface
Pressure exerts force equally in all directions. Because the direction of the force is equal in all directions pressure creates no motion, but contains potential energy that can be used to do work.

30. Roll DROP Stop, Drop & Roll STOP
Stunt people are the only people that get set on fire intentionally, but many people find themselves on fire as a result of accidental exposure to bonfires, matches, cigarettes, and candles. Your clothes can be extinguished using the technique of stop, drop, and roll. This technique works by removing the oxygen from your clothes, which are the fuel.
Stop, Drop & Roll

31. Insulators resist the flow of energy
Any material that resist the flow of energy is an insulator.

32. Choose the right insulator for the job!
So far as fire stunts go, while many insulators block the flow of heat, it is important to remember that not all insulators are fireproof.

33. Components of Fire:
Fuel
Oxygen
Heat
Chemical Reaction

34. Materials that burn faster than the speed of sound are
Detonating
Detonating
Explosions are made by rapidly creating gas. The gas is made from burning a fuel. Fuels that burn faster than the speed of sound are called explosives. Most explosives can either be burned or detonated depending on how they are ignited. To detonate is a term which means to explode violently and noisily.

35. The speed of sound is 1100 feet per secondOr
335 meters per second
Any material which burns faster than the speed of sound will explode violently and noisily when ignited.

36. If you find a gun… Stop. Don’t Touch! Leave the area. Tell an adult.
The guns used in movies are not real. Only three things come out of movie guns: smoke, fire, and noise. Movie guns do not fire bullets. You can’t, however, tell the difference between a real gun and a fake guns simply by looking at them. Therefore, all guns should be handled as real guns. Every one should be taught the four basic rules of gun safety (stop; don’t touch!, leave the area; tell an adult). A very effective program for teaching gun safety to children can be found at
If you find a gun, even if you think it may be a toy don't go near it unless you are with an adult who knows how to properly handle guns. Even professionals can sometimes have a difficult time determining real guns from fake guns.

37. Follow Directions!
An important step toward the successful completion of any science endeavor is to follow directions carefully. Your safety and the safety others often depends on carefully following directions. This is one of the most important steps toward maintaining a safe work environment for yourself and those around you. If a professional stunt coordinator skips this vital step it could result in dangerous explosions or uncontrolled fires which could hurt his crew and the actors involved. Mistakes like that could not only cost him his job but also his life and others. So practice this simple step now and make it a habit!

38. Chemical Reaction Fuel + Heat
Gas + Heat
Explosions can be created by suddenly releasing large amounts of gas. The gas can come from a chemical reaction. When fuel and heat are combined they create a chemical reaction commonly referred to as FIRE! A chemical reaction is the mutual action of substances undergoing a chemical change, or the state resulting from such changes.

39. Law of Conservation of Energy:
Energy can neither be created nor destroyed but can be changed from one form to another.
While we usually need heat to trigger a chemical reaction, we don’t have to start with heat. Often we transmit electricity through wires to the chemicals we want to ignite, and change the electricity into heat at the far end of the wires. This is the easiest way to put distance between ourselves and dangerous chemical reactions.
When a fire is ignited one of the largest reactants, or products, of this chemical reaction is a gas. This is why we don't see much evidence of leftover matter once a fire is extinguished.

40. Electric Circuit Animation
An electric circuit is simply a circle in which electricity travels. Electricity works only when it’s moving. For electrons to move in a circle, or circuit, the circuit must be closed.
A length of electrical wiring acts as a wide "Electron Highway" for electricity, in which electrons are free to move around one another without colliding. At the end of the wiring for an explosive detonation the "Electron Highway" is squeezed down to one lane of traffic. This causes a "jam" in which electrons collide and bounce off of one another, creating friction and heat, which in turn triggers the detonator.

41. Electric Circuit Electric Circuit
In order to make an explosion from a safe distance, I run wires to an explosive and create an ELECTRIC CIRCUIT…
An electric circuit is a complete or partial path over which an electric current may flow.

42. Conductivity Conductivity
…the wires conduct electricity from the battery to the explosive…
Conductivity refers to an object's ability to conduct or transmit heat, electricity, etc. In our case Conductivity specifically refers to the capability of electrical wire to conduct electricity. This property allows us to detonate explosives from a safe distance.

43. Friction
Friction
…at the far end of the circuit the wires become narrow; the narrow wires force electrons to collide, creating FRICTION…
Friction refers to when two or more objects rub against one another, or the resistance to motion of one moving object or surface to another.

44. Heat Heat …the friction creates HEAT…
Heat is a form of energy existing as the result of the random motion of molecules. It is the form of energy that is transferred between materials as a result of their temperature difference.

45. Chemical Reaction Chemical Reaction
…the heat triggers a CHEMICAL REATION…
The chemical reaction created when combining friction and heat is fire. This highly reactive form of energy is used to ignite explosives.
In a chemical reaction the atoms that make up a substance are rearranged to make new substances. The original ingredients are called the reactants and the resulting components are called the products of the reaction.

46. Change of State Change of State Animation
…the chemical reaction causes the reactants to change from one state of matter to another…
Due to the Law of Conservation of Energy, no matter can be destroyed. Instead matter simply changes it's current state. Solid to liquid to gas, vise versa, and/or any combination in between. When a fire is ignited one of the largest reactants, or products, of this chemical reaction is a gas. This is why we don't see much evidence of leftover matter once a fire is extinguished.

47. Solid to Gas
Solid to
Gas
…Solid fuel, when burned, creates gases.

48. Pressure
Pressure
The gas expands, exerting pressure against the walls of the container. When the pressure finds an escape route it moves in that direction creating…
Pressure (P) refers to the force per unit of area.

49. Force
Force
…A force. When the force is applied to an object, the object is moved, shattered, or both.
Force (F) is the cause, or agent, that puts an object at rest into motion or alters the motion of a moving object. Force is exerted in one specific direction while pressure is evenly distributed over a set space.

50. KABOOM!
KABOOM!
All of these factors and principals play a role in creating explosive special effects in the movies.

51. Science in the Movies 1-800-STUNT-FX www.scienceinthemovies.com
For more information, references and entertaining video clips please visit ScienceInTheMovies.com.

52. Steve Wolf
Steve is an experienced stunt and special effects coordinator who is passionate about how exciting science can be. When he heard that US students were ranked among the lowest in developed nations for science knowledge, he decided that he could make a difference. By using the science that he encounters every day in his movie and television work, Steve was able to create a program that makes science exciting and fun for children. Steve also works with teachers to help them use some of the same approaches to teaching science in the movies.