The Relationship Between Potato Length and Range in a Potato Cannon
Introduction | Hypothesis | Method | Diagram | YouTube Money$$ | Materials | Results | Conclusion | Bibliography | Educational Links | Go Up
Background Info
Advances in science have often been dictated by a practical need exhibited by humanity. However, once created, this technology often is applicable to other pursuits. For example, advances in the science of cannons and artillery have been brought about by the simple demands of war, but these advances have undoubtedly helped the development of other devices, such as the potato cannon. In order to gain a better understanding of the potato cannon, its history, the physics involved, and the important related facts will be stated.
The story of the potato cannon starts begins with the story of the cannon. The earliest cannon recorded in human history was said to be invented in by Ctesibius of Alexandria in the 3rd century BC. Ctesibius’ cannon was powered using compressed air. Around that same time, the Chinese were developing a cannon of their own which operated using explosive powders. (1) These devices evolved to become the Chinese flame lance, a bamboo tub used to shoot flames at the enemy. This technology further evolved into a hand cannon utilized by the Chinese and the Japanese. This technology soon spread and was picked up by the Islamic world around 13th century AD. As the technology leaked to Europe during the Middle Ages, the size and variety of the cannon grew. The most recent development of the cannon saga is the development of artillery guns in the 20th and 21 century (1).
A cannon uses rapid combustion, one of seven types of combustion. Rabid combustion occurs when large amounts of heat and light are released at one time. In our cannon, since we used hairspray as a gas, the hairspray burned up almost instantly due to the large amounts of heat and light particles being released. This process is commonly known as an explosion (2).
To understand how the potato will fly, understanding drag and aerodynamics is necessary. Their are many aspects to drag when it is applied to physics. For how the potato will fly, it is drag in aviation. Pilots use something called the power curve, which helps pilots understand when more thrust is needed to keep an airplane in flight. The same aspect is used with potatoes, minus adding thrust. The weight of the potato will determine how fast and how far the potato will go before it starts to slow down and will hit the ground. (3,4).
Our cannon operates much like the combustion based cannons of the past. In our experiment, used a plastic potato cannon that uses hairspray for combustion. The cannon consists of a long plastic barrel, a plastic canister base, a plastic unscrew able end cap, and a barbeque igniter attached to two wires. The cannon shoots potatoes at high speeds. We will be testing the relationship between the size of the potato chunk being launched and the distance it goes.
The larger potato chunks will go farther because they have a higher mass, and Force is equal to the mass * Acceleration.
Variables
Our manipulated, or independent, variable was the size of the potato. We cut potato lengths at 1, 1.5, 2, and 2,5 inches. Our dependant variable was the distance the potato reached. The cross sectional area of the potato stayed constant throughout the experiment. The variable that were kept constant were the launch angle, the amount of hairspray used for each launch (spray time kept constant), and the diameter of potato (cross-sectional area constant.
Before we started launching, we pre-cut all the potatoes that we shot. We used a metal cylinder that was the same as the inner diameter of the cannon barrel. We then cut the potatoes into four different lengths: 1 inch, 1.5 inches, 2 inches, and 2.5 inches. Once we had six of each potato, we were ready to rumble!!! When we arrived at the launch site, we pre-marked distances from zero to 500 feet in increments of 25 feet. We also marked where the cannon was to lay so when we fired, we fired from the same exact spot and angle. To load the potato, we would place it in the barrel and then shove it down with a marked ram rod to a particular point. To launch the cannon, we would spray hairspray into the chamber for four seconds and then seal the chamber with a firing cap. Once loaded, we would set the cannon up in firing position, hit the igniter, and BOOM goes the dynamite!!! Once fired, our spotter would mark the landing zone and measure its exact distance in feet with the help of the markings and a tape measure. We repeated this process until all the potatoes were launched.
http://www.youtube.com/watch?v=5t9_l9sJj8A
- 24 Potatoes
- 1 Combustion Cannon
- 1 Plastic Box
- Electrical Wiring for Ignition
- 1 Potato Cutter
- 1 6ft Long Wooden Ram Rod
- Hairspray Bottle
- Tape Measure
- 1 Spotter
Raw Data (Excel) | Raw Data (Text)
| Length (in) | 1 | 1.5 | 2 | 2.5 |
| Trial Number | Launch Distance (ft) | Launch Distance (ft) | Launch Distance (ft) | Launch Distance (ft) |
| 1 | 284 | 327 | 349 | 406 |
| 2 | 268 | 324 | 356 | 412 |
| 3 | 275 | 332 | 347 | 393 |
| 4 | 301 | 321 | 361 | 386 |
| 5 | 286 | 311 | 364 | 403 |
| 6 | 271 | 298 | 344 | 416 |
| Average | 280.8333333 | 318.8333333 | 353.5 | 402.6666667 |
In our experiment we discovered that the larger potatoes consistently traveled a larger distance than the smaller potatoes. Our graph or\f the different velocities in terms of the length clearly shows a direct relationship. This confirms our hypothesis, however our reasoning for this hypothesis was wrong (we got lucky). After further exploration we believe that the reason the potatoes travel faster is not because their mass gives them more force, but instead because their larger mass creates more pressure within the cannon, thus causing a larger explosion. The range equation describes the range as a relationship to the square of the velocity, therefore, from the linear relationship it can be assumed that the velocity is related to the square root of the speed. There were several sources of error within this experiment. These include wind, which would manipulate distance and accuracy, also some of the hairspray escaped the chamber while being sprayed, which could affect the amount of combustion. We also realized that the strength of the cannon decreases very slightly with each firing. We believe this is due to excess potato residue within the barrel. Also the masses were not consistent for each alternate length. To improve this experiment I would conduct it inside a large indoor facility to reduce wind, use different cannon for each firing and develop a method to spray the hairspray into the tube through a tube or some other apparatus, to minimize variation in amount of fuel.
- “Small Cannon History” (1) http://en.wikipedia.org/wiki/Air_resistance# Drag_in_aerodynamics - We used this link to learn about the function of small scale cannons. It helped with the construction and operation of the cannon.
- "Combustion." – Wikipedia (2) http://en.wikipedia.org/wiki/Combustion- Showed us the basic concept of fuel combustion and how it would apply to our experiment.
- “Aerodynamics” – Wikipedia (3) http://en.wikipedia.org/wiki/Aerodynamics- Used for developing a hypothesis for our experiment, considering our aim was to discover which size potato would be the most aerodynamic.
- “Drag (Physics)” – Wikipedia (4) http://www.cannon-mainia.com/history.htm -Additional information to help us design our hypothesis. In the formulation of it, we mainly considered air resistance, drag, and which angle would give the potatoe an ideal initial velocity/momentum.
- “Potato Cannons” www.rose-hulman.edu/Catapult2004II/groups/group05.doc - More information about potato cannons in general, used to further expand our vast amounts of knowledge on the subject.
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