It might seem weird to look to the world of cartoons to learn about the physical laws that govern the real world, but in the middle of all the crazy capering, wild explosions, unlikely chase sequences and downright impossible action scenes, sometimes cartoons get physics right. Because physical actions are so often exaggerated in animation, it can actually be easier to see forces at work. Of course, sometimes it's just a really good quantum mechanics pun.
These 10 examples from our favorite cartoons show times when zany laws of cartoonland gave way to the actual laws of physics (but still stayed zany).
On several occasions, the Flash has vibrated his molecules using his superspeed powers, then passed through a seemingly solid object. What's going on here? A rather unlikely extrapolation of a concept known as quantum tunneling.
Quantum tunneling is the means by which very small particles, usually electrons, are able to pass through very thin layers of impassable materials. It depends on quantum mechanics, the way particles act at very small scales. Specifically, it depends on particle/wave duality -- at quantum scales, particles exhibit properties of both a particle and a wave. It's impossible to determine the exact position of a particle -- instead, a particle exists as a cloud of probabilities. When a particle crashes into a thin barrier, there's a tiny probability that the particle exists on the other side of the barrier. Crash enough particles and some of them will turn out to actually be on the other side when measured. Despite the name, they don't actually tunnel through the barrier. They simply appear on the other side. This isn't just theoretical -- electron tunneling microscopes measure the number of electrons tunneling through thin materials to get incredibly precise images.
How does this work for the Flash? Quantum doesn't work at macro scales. That is, entire objects can't quantum tunnel through brick walls. Presumably, Flash is vibrating his molecules to give each molecule many, many opportunities to appear on the other side of the wall. While the concept is realistic, there's actually no way a large object could quantum tunnel though anything as thick as a wall.
In the episode "The Route of All Evil," the "Futurama" gang tries to find good beer. In their search, they come across St. Pauli Exclusion Principle Girl beer. It's a reference to the German-brewed St. Pauli Girl beer, perhaps most well known for their logo featuring a blonde woman in traditional garb.
More importantly, it's a reference to the Pauli Exclusion Principle, a law of quantum physics first described by physicist Wolfgang Pauli (who was Austrian, not German) in 1925. The principle explains that particles with a certain kind of spin (an intrinsic property of quantum particles) can never occupy the same quantum state.
While the nature of quantum states and particle spin can be difficult to grasp, the results of the exclusion principle are easy to see. Without it, we wouldn't have different elements with different properties, like oxygen, copper, plutonium, hydrogen, carbon or anything else on the periodic table. Without elements, there wouldn't be much of anything in the universe. This is because the Pauli Exclusion Principle is what forces electrons into different energy levels, or shells, around the nucleus of an atom. Those different electron energy levels are what give elements different properties and allow them to interact and form new elements and chemical reactions. Thanks, St. Pauli Exclusion Principle Girl!
When Wall-E needs to leave a self-destructing escape pod in a hurry, he uses a fire extinguisher as a propulsion system, rocketing his way to safety. Wall-E was relying in Newton's third law of motion, which is commonly rendered as, "Every action has an equal and opposite reaction." More accurately, all forces result from the interaction between two objects, and when two objects interact, they apply an equal amount of force to each other, with the forces acting in opposite directions. A bat applies force to a baseball, and the baseball applies an equal amount of force to the bat, but in opposite directions. The difference you see in movement is due to Newton's second law of motion (a=F/m, commonly rendered as F=ma), which shows that objects with a lot of mass don't accelerate as much. When you bounce a tennis ball off a brick wall, the wall does accelerate, but if you plug its mass into the second law equation, the acceleration is so small you don't notice it.
In Wall-E's case, the two objects were Wall-E himself (including the fire extinguisher, which he was holding onto tightly) and the compressed gas inside the extinguisher. When he activates the extinguisher, the gas shoots out with a certain amount of force. An equal amount of force pushes Wall-E in the opposite direction.
Is this plausible? While fire extinguishers vary greatly in the amount of gas they contain and how much pressure they're under, it's definitely within reason that a large extinguisher could propel Wall-E at impressive speeds, especially considering Wall-E's low mass.
In the episode "The Late Philip J. Fry," Fry and friends go billions of years into the future and witness the end of the universe, with all the stars and galaxies exploding and fading into nothing. This roughly jibes with one theory of the end of the universe, in which all matter and energy becomes so uniformly spread out it no longer interacts with itself, creating a stasis known as "heat death." Professor Farnsworth's throwaway line, "There's the last proton decaying," is a little iffy -- in the most common physics models, protons don't decay.
The end of the universe isn't the end for our characters, however. They witness a new Big Bang and the birth of a new universe, which plays out identically to the old universe (even down to Leela waiting for a chronically late Frey in the same restaurant that she did in the old universe). While the concept of the Big Bang is accurate in a very general sense, "Futurama" doesn't depict it accurately. The Big Bang was not an explosion in space; it was an explosion of space. In the Big Bang, space itself expanded from an infinitely small point. You couldn't witness the Big Bang from an external location unless you were outside the universe (and because they eventually return home we know that Frey, Farnsworth and Bender are still inside the universe).
The repeated death and rebirth of the universe is conceptually accurate in some cosmological models, although it could happen by many different mechanisms. Most commonly, the universe could shrink back down to a point instead of experiencing heat death. That point (a singularity) would eventually undergo another Big Bang and restart the process.
The classic 1940s Superman cartoons from Fleischer Studios laid the cornerstones of Supes' pop culture superstardom. "Look! Up in the sky!" A great example of Superman battling the laws of physics is an episode titled "Billion Dollar Limited," in which he must stop a runaway train filled with the largest gold shipment ever transported. The train careens down a slope, and Superman stops it by grabbing the last car and pulling it back up the hill. It's a beautiful illustration of an inclined plane.
When you push on an object or surface (including standing on the ground), a force called the normal force exerts an opposite and equal amount of force. This is actually the force created by the microscopic compression of atoms, and it's what makes solid objects solid. The important thing is that the normal force always acts perpendicular to the surface.
With an inclined plane, like the slope the train is rolling down, the train is pushing down on the slope (due to gravity) and the normal force pushes back an equal amount. Those forces are balanced. However, gravity is pulling the train straight down, not perpendicular to the surface, so some component of the gravitational force is acting parallel to the slope, pulling the train downhill. The exact amount of that force can be calculated if we measure the angle of the slope and know the weight of the train. This calculation is expressed through the equation F = mg*sin Ɵ.
There are two things counteracting that downward force -- friction and Superman. Figuring out exactly how much force he needs to pull the train up the hill is complicated and beyond our scope here (there are different kinds of friction involved, we don't know how much the train cars weigh, and so on). One thing's for certain: The narrator isn't kidding when he says Superman is, "more powerful than a locomotive."
In the classic Simpsons episode "Deep Space Homer," Homer goes to space aboard the space shuttle. While in orbit, Homer experiences realistic weightlessness. While Homer's flight (and the flight of his potato chips and ant overlords) is accurate, your ideas about why Homer and real astronauts are weightless in orbit might not be.
The farther you get from Earth, the less gravity affects you. However, in an Earth orbit, this reduction of gravity is minimal, reducing gravitational force by roughly 10 percent. So an absence of gravity can't explain astronauts and Homer floating around, seemingly weightless.
So what makes Homer float? Free fall. When you're on Earth, you never experience gravity directly. It is a force that acts at a distance, and it's impossible to feel. You only feel contact forces, like a dodgeball hitting you in the shoulder, or the ground pushing up against your feet (which we've learned is called the normal force). If you could somehow eliminate all the contact force, you would experience a feeling of weightlessness, even though your actual weight and the actual gravitational force acting on you remain the same. You get a glimpse of this on a roller coaster as it goes over a sharp rise. In an orbital vehicle, it's as if the astronauts are constantly going over the top of that roller coaster. They're falling, but the space shuttle is also falling away from them, in a constant perpetual free fall around Earth. With no contact forces, they don't experience their own weight. They feel (and appear) weightless.
In the episode "Careers in Science," Gargantua-1 is a massive space station that has seen better days. It's described as having a geosynchronous orbit, although it isn't clear if it's also geostationary. A geosynchronous orbit means the satellite has the same orbital period as Earth. Therefore the satellite will cross the same spot in the sky (relative to an observer on Earth) at the same time every day. This doesn't mean it will appear to stay in the exact same spot in the sky, since the satellite may be orbiting at an inclination from the equator. To explain that another way: As Earth rotates, a stationary observer on the ground is moving directly from west to east, while the satellite may be moving at some north-south angle (and is not necessarily ever directly overhead). Because the orbital period is the same, the satellite "meets" the same spot in the sky at the same time each day.
A geostationary orbit is a special case in which the satellite orbits along the equator, allowing it to maintain the same relative spot in the sky. This concept is widely credited to science-fiction author Arthur C. Clarke.
In practice, a satellite (or space station) in geosynchronous or geostationary orbit needs to periodically use thrusters to keep itself in the proper orbit. SPOILER ALERT: This may explain why Gargantua-1, in serious disrepair and experiencing a problem that may or may not have been urine-related, eventually drops out of orbit and crashes.
Our favorite confused snowman, Olaf, experiences a lot of physics, with all the falling, tumbling, sliding and crashing into things he does in the course of Disney's "Frozen."
Although Olaf is made of snow, he's mostly treated as a solid object. When Olaf falls off a cliff, he first experiences acceleration due to gravity. The force of Earth's gravity accelerates Olaf toward Earth. We could calculate this with Newton's second law, a=F/m. Since he's made of snow, Olaf is probably not very dense, so you might think he wouldn't accelerate as quickly as if he were made of solid ice. However, all objects in free fall accelerate at the same rate, regardless of their mass. At some point, though, he will reach terminal velocity, the point at which the drag of air pushing on him equals the acceleration due to gravity, and he accelerates no more. This is an important physics concept, because terminal velocity does not depend on Olaf's mass, but rather on his shape. More open or spread out shapes create greater drag, resulting in a lower terminal velocity. This is why a parachute works -- it doesn't make the skydiver any lighter, it just increases her drag.
When Olaf hits the ground at the bottom of the cliff, he experiences deceleration (which is a form of acceleration). Could a living snowman actually survive such a fall? Lucky for Olaf, there's a thick layer of snow on the ground. That means his deceleration is spread out over a few extra fractions of a second, compared to landing on solid concrete. That makes all the difference, because spreading out the force imparted to Olaf over a longer period reduces the damage it will do to him, just like the air bags in your car slow down the deceleration of your body in a crash.
To foil a group of crooks, Mr. Incredible drops a tree trunk in front of their speeding car. The car comes to a metal-crunching halt, but the bad guys continue moving forward until they smack into the dashboard and windshield, incapacitated. This is Newton's first law at work. It says that an object will keep doing whatever it's already doing until some force makes it do something else. You may have heard it phrased, "An object at rest tends to stay at rest; an object in motion tends to stay in motion," or just the law of inertia.
This law can seem counterintuitive at first, because here on Earth there are a bunch of invisible forces acting on objects at all times that cause them to seemingly violate Newton's first law. If you throw a ball, shouldn't it keep going forever? It would in space, but on Earth the ball is slowed by friction from passing through air, and eventually gravity makes it fall to the ground (where even more friction makes it come to a stop).
In the case of the guys in the car, they're moving forward, pushed by the normal force of their seatbacks. When Mr. Incredible brings the car to a sudden stop, the crooks keep moving forward, in accordance with Newton's first law. However, it isn't air resistance or gravity that slows them down, it's the solid objects in front of them -- the dashboard and windshield. Those objects impose a force on the baddies, causing them to stop moving (and, as is the case with the car, the sudden deceleration causes some physical damage).
This scene from "Toy Story 3" is a great parody of the classic "Mission Impossible" ceiling drop gag. In the scene, Woody hangs from a tree, caught by his pull string. Then the string retracts, activating his built-in voice recording. The physics here is fairly straightforward -- we're measuring the net forces at work on Woody to see how and if he moves.
At first, Woody is falling, accelerating toward the ground due to gravity. The string gets caught on a tree, so now there's a force counteracting gravity: The tension force of the string is pulling Woody up. For a second, the tension force is equal to the gravitational force, so Woody hangs motionless. The net forces acting on him are in balance.
Then some mechanism in Woody activates, presumably a spring that winds the string up inside him. The spring applies extra tension force to the string (we can treat the spring as part of Woody, in terms of determining which forces are acting on which objects). This increase in the tension force exceeds the gravitational force, so Woody begins accelerating upward. However, he stops accelerating and then moves up at a constant pace, meaning the forces balanced out again. The spring had a little extra oomph at the start to get Woody moving, apparently.
The history of animated movies is rich and fascinating. Learn about the creators of the first animated movie at HowStuffWorks.
Author's Note: 10 Outrageous Cartoon Moments That Use Real Physics
I always learn a lot when I research and write a HowStuffWorks article, but this one was a serious crash course in physics. I'd understood a lot of these physical laws on a conceptual level, but really drilling down and looking at the formulas gave me a much deeper understanding. I was knee-deep in calculating Superman's pulling force on the inclined plane at one point, but had to cut that out because it was too long. I got a lot of help from my wife, who is a high school physics teacher.
- Australia Telescope National Facility. "The Big Bang and the Standard Model of the Universe." (July 2, 2014) http://www.atnf.csiro.au/outreach/education/senior/cosmicengine/bigbang.html
- Blickenstaff, Jacob Clark. "To College and Beyond? Science in Toy Story 3." NSTA. July 13, 2010. (July 2, 2014) http://www.nsta.org/publications/news/story.aspx?id=57577
- The Engineering Toolbox, "Body Forces on Inclined Planes." (July 2, 2014)http://www.engineeringtoolbox.com/inclined-planes-forces-d_1305.html
- Hyperphysics, "Barrier Penetration." (July 2, 2014) http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/barr.html
- Hyperphysics, "Pauli Exclusion Principle." (July 2, 2014) http://hyperphysics.phy-astr.gsu.edu/hbase/pauli.html
- MinutePhysics, "What is Quantum Tunneling?" (July 2, 2014) https://www.youtube.com/watch?v=cTodS8hkSDg
- The Physics Classroom, "Inclined Planes." (July 2, 2014) http://www.physicsclassroom.com/class/vectors/Lesson-3/Inclined-Planes
- The Physics Classroom, "Newton's Second Law." (July 2, 2014) http://www.physicsclassroom.com/class/newtlaws/Lesson-3/Newton-s-Second-Law
- The Physics Classroom, "Newton's Third Law." (July 2, 2014) http://www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law
- The Physics Classroom, "Weightlessness in Orbit." (July 2, 2014) http://www.physicsclassroom.com/class/circles/Lesson-4/Weightlessness-in-Orbit
- Protec, "Protec Carbon Dioxide Fire Extinguisher." (July 2, 2014) http://www.aespl.com.sg/pdf/FIRE%20EXTINGUISHER-CO2.pdf
- Science Daily, "Geosynchronous Orbit." (July 2, 2014) http://www.sciencedaily.com/articles/g/geosynchronous_orbit.htm