Ernesto Figueroa
6842290647
Illumin Article
5/2/14
Engineering Isn’t All Fun and Games… Unless It’s Air Hockey
It is not every day that phenomena occur that seems to defy the laws of nature. Every so
often there is some kind of human innovation of technology that appears to do just that.
Hovercrafts are vehicles that seem to neglect the laws of physics and have become a prime
example of how understanding simple physics concepts can be utilized to make it appear as if the
laws of physics are a thing of the past. The mechanisms of how such an outstanding
accomplishment and feat of engineering works may intimidate those who are interested in all the
details and explanations, however in this case it is actually quite simple and can be a lot of fun to
learn. As we explore the underpinnings of how a hovercraft operates, we need not to go to the
nearest local library nor back to a well-respected professor to give oversight into the topic; all
that is needed is a trip to the local arcade. Yes, understanding the context of this marvel can
come in the form of a game. This game takes engineering and physics’ principles and utilizes
them in a way to create an experience that has continued to be passed down from generation to
generation. This game is Air Hockey.
Air Hockey has been around since the early 1970’s and has been a staple for any arcade
they were in. The game of Air Hockey is just what it sounds like. It is hockey played on air. Yes,
on air. It involves 2 players who face off against each other trying to knock the puck into the
other person’s goal [1]. It is virtually identical to its arcade counterpart PONG (Fig 1), but the
catch is it is played on a special table designed to make the puck “float”. This table has tiny holes
on the surface that continually pump a jet of air from underneath. The combination of these air
jets and the specially designed puck, causes it to “lift” off of the surface and become practically
Figueroa 2
frictionless as the opponents send it ricocheting back and forth [2]. How does this relate to
hovercrafts you may ask; the name “hovercraft” was given thanks to its ability to “hover” off of
the ground [3]. Air Hockey and hovercrafts use the exact same principles to defy physics.
Understanding a simpler example, Air Hockey, will give all the insight and knowledge that is
needed into understanding exactly how a hovercraft operates.
Figure 1: PONG Videogame
Figure 2: Air Hockey Table
Gravity and Friction:
An incredible feat of engineering has to be implemented in order to continuously neglect
two of the most common forces of nature: gravity and friction. Gravity is responsible for the
weight of all physical objects. It is defined as the force of attraction one object has to another;
basically, how “hard” the Earth pulls down on an object. This force is constantly around us and
acts on everything. There is no way around the pull of gravity; which is why there are no objects
that float in air (balloons only float due to what is inside of them. The balloon itself cannot avoid
gravity’s pull). Back to Air Hockey; the puck is constantly being pulled down and is forced to
rest on top of the table’s surface (just as a book rests on top of a desk). This constant rubbing
against the surface leads to our next engineering obstacle, Friction.
Friction is the force that resists motion. It is responsible for
objects’ abilities to remain in one spot and to start slowing down
once in motion, eventually coming to a complete stop. Back to the
Figure 3: Holes on the surface of the table
with the outline of a puck for size reference.
Figueroa 3
book analogy; the book will not move once it is placed down on the desk. The reason for this is
the friction that is caused by gravity. The book, even with gravity present, would still have the
ability to move around if it weren’t for friction. The way friction works is the molecular bonds
between the two surfaces in contact tend to cohere to one another when a force is applied. In
other words, when gravity pushes one of the objects down it acts as Velcro and “attaches” to the
surface. This attachment exerts a force that needs to be matched in order to move; while in
motion it also needs to be matched otherwise the force from friction will slow the moving object
down. Thus friction needs to be overcome in order to have the puck speed across the table. How
can these two forces, gravity and friction, be overcome in Air Hockey? Well there has yet to be a
discovery on how to turn off gravity so friction comes into question. To go about avoiding
friction you need to go back to the definition. “A force that resists the relative motion or
tendency to such motion of two bodies or substances in contact” [4]. Substances in contact. What
if the puck and table weren’t in contact? There would be no friction between the objects because
they aren’t touching. This is precisely what engineers did. They created a pocket of air that the
puck sits on to avoid exhibiting friction to the table.
Does this correlate back to the ability of a hovercraft to hover? Absolutely. Gravity pulls
the hovercraft down just as it does to the puck. Friction also plays a role and is even more of an
effect when it comes to hovercrafts since they are typically not on top of a smooth surface, unlike
that of the Air Hockey puck. Both of these forces will need to be overcome before any kind of
motion would be present. If you haven’t made the connection already, the way to overcome this
dilemma is indeed a similar pocket of air in order to reduce the amount of friction between the
hovercraft and the earth that it will be voyaging over.
Lift:
Figueroa 4
The key engineering marvel of this game is the ability to create a puck that is virtually
frictionless. Every Air Hockey table consists of hundreds of tiny holes aligned uniformly all
throughout the area of the table. On the underside of these holes is an air compressor that will
blow a continuous stream of air through each and every hole. The combination of the holes and
the air compressor create the necessary lift that is needed to negate the force of gravity and thus
reducing friction. Lift is the force that opposes gravity. Gravity pulls objects down, while an
object that has a lift force would go up (or counteract only a portion of
the gravity thus making the force of gravity less than what would be
felt without the added lift). Because the holes are uniformly placed on
the surface of the table, no matter where the puck happens to be there
will always be a continuous and evenly distributed lift force that
Figure 4: Generic Air Hockey Puck
pushes up against the puck in order to maintain its state of reduced friction.
The puck itself also plays a key role in aiding in lift. Air Hockey pucks are not only made
out of light plastic to reduce their weight but are specially designed to create a pocket of air that
is used to separate the puck from the table, thus reducing even more friction. The ridges found
near the perimeter of the puck act as a skirt that traps some of the air coming from underneath
the table. This trapped air acts as an air pocket that the rest of the puck can “sit” on [5]. Once this
recess is filled with air, the air is forced to escape from underneath the perimeter of the puck.
This air that escapes goes underneath the portion of the
puck that is in contact with the surface. Less of the
surface in contact with the table then results in less
Figure 5: Air Hockey puck diagram showing how the pocket
of air creates an artificial cushion beneath the puck.
friction; less friction results in greater speed that the
puck can obtain and ultimately faster paced play.
Figueroa 5
Real World Applications:
Air Hockey is cool and all but it’s only a game right?
Wrong. Air Hockey is itself only a game that is played as a
form of entertainment but the same principles engineers used
to create this game are also used to create hovercrafts.
Hovercrafts are considered to be a hybrid vehicle that is
capable of traveling at high speeds over terrain most normal
vehicles would not be able to. They can travel over water to
Figure 6: Hovercraft and skirt component
sand to mud to ice all in a single run. These have already been utilized historically for
commercial transportation uses, novelty items, and even in the military. All from principles that
are found in an arcade game.
There are no true hovercrafts in the truest sense of the word but rather ACVs (AirCushioned Vehicles). These vehicles are identical to the Air Hockey puck; a pocket of air is
utilized in order to separate as much of the surface of the vehicle from the ground, thus reducing
friction. ACVs have a flexible skirt underneath the vehicle in which the pocket of air is held [7].
These skirts are typically made from some sort of composite material that is flexible and
lightweight in order to reduce the amounts of weight and the properly function, but are also
sturdy and durable enough to not breakdown and rip midway through a ride. Currently, there is
no perfect median between lightweight and strength for this skirt so any material that is utilized
tends to eventually fail do to the other constraint (i.e. One material is light enough but too weak,
while another is durable enough to last but ultimately weighs down the vehicle to negate any lift
produced).
Figueroa 6
Instead of needing to rely on a table to blow air up into the skirt, ACVs rely on their own
fans and compressors to blow air downwards into the skirt [6]. Once these air pockets get filled,
the air then escapes down and underneath the vehicle causing it to ever so slightly lift off the
ground. As aforementioned, lift is the key to allowing an Air Hockey puck, and its hovercraft
counterpart, to reduce the forces of friction. This reduction of friction is what truly sets this
vehicle apart from the rest. No other vehicle has utilized this sort of technology and it still
amazes audiences to this day. With reduced friction, less fuel is needed in order to propel the
vehicle and faster speeds are more easily attainable. Due to the lift, there is another easily
overlooked significance; there is less force that pushes on the ground by the vehicle. One
professional golfer took this knowledge and decided to convert his golf cart into a hovercraft [8].
This allowed him to take his new golf cart places traditional golf carts could not. Not only could
he traverse from grass to sand trap to water with ease, he could also drive over the green because
the amount of force delivered from the vehicle was so incredibly small. Typically, even a person
who walks across the green will leave footprints but astonishingly this vehicle could traverse
over it time and time again without leaving a mark.
With the technology to “hover” above the ground already been implemented in the past,
one would certainly think hovercrafts would be more common than they are. Unfortunately,
there are too many downfalls currently present. One of the most disastrous is the fact that these
vehicles lack maneuverability. Hovercrafts lack contact with the ground so the only way in
which they can move is by air. In order for the vehicle to be put into motion, air would have to
be blown in the opposite direction of travel to push it along [9]. This feat is far easier said than
done. One small deviation from the intended angle the fans need to be placed in can be
catastrophic. While maneuvering, if the fans aim too high the vehicle would be pushed into the
Figueroa 7
ground, if they are aimed too low no forward movements would occur. Even the most successful
hovercrafts have trouble maneuvering exactly the way the driver intends to. Progress has been
made but it is still unreliable at this time.
Other problems deal with the weight and amount of lift that is required. In order to
produce more lift, either more air is needed or less weight is required. Hovercrafts can only be so
light; they still need to be structurally sound in order to function. However, the production of
more air also increases the amount of noise produced by the hovercraft. There are no silent Air
Hockey tables, as an easy reference to understand the dilemma, due to the fact that an air
compressor is required in order to function. Similarly, noise reduction in hovercrafts has not
progressed far enough to the point that comfortable decibel levels have been attained [10].
Conclusion:
Air Hockey is much more than a game that you might find in the corner of some arcade.
It is a true engineering masterpiece. Every aspect has been meticulously fabricated in a way that
would help to overcome the natural forces of nature. Although creating a truly frictionless game,
and vehicle, is impossible, Air Hockey and hovercrafts comes close. From the way the holes in
the table are placed, to the design of the puck itself, the engineers constructed their game in such
a way to reduce all the friction between the puck and the table as possible allowing for faster
puck speeds and ultimately more fun. The engineering goes beyond just a game though. It can
be a learning tool utilized to understand how hovercrafts work. These same principles may
someday become what the future is reliant on. Slowly engineers will be defying the laws of
nature one step at a time.
Figueroa 8
References
[1] Dexheimer, Eric. “Married to the Mallet.” Denver Westwood 21 November 2002
[2] Jacobson, Mark. “Gone with the Wind.” Village Voice 17 November 1974
[3] Herring, Sharolyn, and Christopher Fitzgerald. "History of the Hovercraft." Neoteric
Hovercraft, Inc 17 (2006).
[4] friction.(n.d.) The American Heritage® Science Dictionary.(2005).Retrieved February 21
2014
[5] Grant. Dimpled air hockey puck. US 7207909 B2. 2005
[6] Bill Gunston, "Hydrofoils and Hovercraft: new vehicles for sea and land", Doubleday, 1969,
p.93
[7] Pendzich, Jerome S. "Vertical lift vehicle." U.S. Patent No. 7,481,290. 27 Jan. 2009.
[8] Kay, Emily. "Bubba Watson's hovercraft golf cart to debut at Ohio course." SBNATION.
Vox Media, 8 July 2013. Web. 29 Apr. 2014.
[9] Wang Cheng-long; Zhang Hong-yu; Fu Ming-yu, "Motion control of an amphibious
hovercraft based on fuzzy weighting," Communication Technology (ICCT), 2012 IEEE
14th International Conference on , vol., no., pp.1006,1011, 9-11 Nov. 2012
[10] Burke, Richard E. "Noise levels of Hong Kong marine craft." The Journal of the Acoustical
Society of America 72.S1 (2005): S46-S46.