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To investigate the effect of varied amounts of sodium bicarbonate paste on the height that a vinegar and sodium bicarbonate rocket reaches after being launched.
For full comprehension of the processes occurring in this experiment it is critical that the following topics are understood: Newton’s three laws of motion, how they are related to rocket launches, the mechanics of the rocket being used in this experiment and how Newton’s three laws of motion relate to it.
Sir Isaac Newton was one of the greatest scientists of all time. In 1686 he presented his three laws of motion. The first law stated that: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied (csep10.phys.utk.edu). “This means that there is a natural tendency for objects to keep on doing what they’re doing. All objects resist changes in their state of motion. In the absence of an external or unbalanced force an object in motion will maintain its state of motion” (teachertech.rice.edu). Likewise, if an object is at rest (stationary) it will remain at rest without the application of an external or unbalanced force (exploration.grc.nasa.gov).
Newton’s second law stated that: The relationship between an object’s mass, its acceleration and the applied force is: F= ma (csep10.phys.utk.edu). In other words “heavy objects require more force to move the same distance as lighter objects” (teachertech.rice.edu).
Newton’s third law stated that: For every action there is an equal and opposite reaction (csep10.phys.utk.edu). “This means that for every force there is a reaction force that is equal in size but in the opposite direction. That is to say that when an object pushes another object it gets pushed back in the opposite direction equally as hard” (teachertech.rice.edu).
Rockets incorporate all three of Newton’s laws of motion. When a rocket is sitting on its fins (pushing down on the earth) it is balanced by the earth’s equal and opposite reaction as is described in Newton’s third law (exploration.grc.nasa.gov). There is no external or unbalanced force and therefore the rocket would indefinitely stay immobile. When the rocket’s engines are ignited, thrust (unbalanced force) is added. When the weight (pushing downwards) of the rocket is less than the thrust (pushing upwards) created by the engines, the rocket accelerates upwards (exploration.grc.nasa.gov). This is explained by Newton’s first, second and third laws of motion.
The rocket being used in this experiment is a film canister rocket. A vinegar and sodium bicarbonate paste is placed inside the film canister with five millilitres of additional vinegar, and then placed upside-down on a plate or saucer. When the vinegar and sodium bicarbonate mix together a fast chemical reaction occurs. Although there are several products produced during the reaction, it is the carbon dioxide gas that forces the lid to be blown off the canister (www.csiro.au).
The more carbon dioxide that is produced, the more the carbon dioxide molecules are squashed together and push or apply force against the inside surfaces of the canister, including the lid (www.csiro.au). As the carbon dioxide builds up, so does the pressure inside the canister, and this pressure quickly forces the lid to be blown off (www.csiro.au). The carbon dioxide pushes down on the lid, but as it is sitting on the plate or saucer, it cannot go anywhere. However, the carbon dioxide is additionally pushing on the inside base of the canister and this is the force that pushes it into the air along with the thrust created in the reaction caused by the canister pushing against the plate or saucer (Newton’s third law of motion).
Like standard rockets, the film canister rocket incorporates all three of Newton’s laws of motion. The lift off of the rocket is due to the application of an external or unbalanced force (First Law) (www.spacesociety.org). “This is the force produced when the lid blown off by the carbon dioxide gas formed in the canister. The rocket travels upward with a force that is equal and opposite to the downward force propelling the gas, and lid (Third Law). The amount of force is directly proportional to the mass of the vinegar and gas expelled from the canister and how fast it accelerates (Second Law)” (www.spacesociety.org).
Safety Goggles were put on and one of the plastic plates was placed on a flat surface of the ground. Ten metres from the plate was additionally measured and marked with the second plastic plate.
A thick paste consisting of twelve teaspoons of sodium bicarbonate and twenty millilitres of white vinegar was made in the plastic bowl.
One teaspoon of the solution was measured with the teaspoon and put into the lid of the canister before five millilitres of white vinegar was measured with the measuring cylinder and placed in the body of the canister.
The lid was put on the canister and it was turned upside down on the first plate. All participating in the experiment were also positioned behind the second plate.
Once the rocket had launched, the angle of elevation of the rocket at its peak height was measured with the clinometer and recorded into the data table as is shown in the apparatus.
Steps three to five were repeated twice more.
Steps three to five were repeated three times, except with half a teaspoon of sodium bicarbonate paste instead of one.
Steps three to five were repeated three times, except with a quarter of a teaspoon of sodium bicarbonate paste instead of a half.
Using trigonometry, the recorded angles were used to calculate the heights reached by the rocket, taking into consideration the height of the person who took the measurements.
The results show that the amount of sodium bicarbonate paste added to a vinegar and sodium bicarbonate rocket did have a substantial affect on the results. It was found that when one teaspoon of sodium bicarbonate paste was added to the rocket the force (carbon dioxide gas) that was produced during the reaction was not large enough to overcome the other forces acting upon the rocket, to propel it into the air. It was additionally found that the rocket was propelled highest with ¼ of a teaspoon of sodium bicarbonate paste reaching an average height of 7.30 metres, followed by ½ a teaspoon reaching an average height of 5.43 metres. This was not what was hypothesised from the research that was conducted, and can only lead to the assumption that when one teaspoon of sodium bicarbonate paste and five millilitres of vinegar were mixed, the balance that was created between the two reactants was not one that would result in maximum output from the reaction.
Problems were encountered during the conduction of the experiment, which led to incomplete results. It was planned for the amount of sodium bicarbonate to be changed twice rather than once but certain conditions did not allow for this to occur. Sodium bicarbonate is an alkali and vinegar is an acid, and when they react together they neutralise each other creating amongst other things carbon dioxide gas.
The carbon dioxide gas is the force that lifts the rocket off the ground and when a balance between the two (sodium bicarbonate and vinegar) was not reached the reaction did not create enough force to overcome the other forces acting upon the rocket, and as is stated by Newton’s first and second laws of motion, was therefore unable to propel the rocket into the air. This furthermore prevented one teaspoon of sodium bicarbonate paste from being counted as a changed variable. Additionally, another problem that was encountered during the experiment was that the time at which the rocket launched could not be controlled. It was unknown when the rocket would launch into the air and this consequently made the angles of elevation very hard to measure and very inaccurate.
Errors were additionally experienced during the course of the experiment despite the caution that was taken to avoid them. The accuracy of the angles recorded by the clinometer was not high. It was difficult to measure the exact angles of elevation from the person measuring, to the maximum height that the rocket reached, as it could not be predicted when the rocket would launch. Parallax error was additionally experienced while measuring the amounts of vinegar and sodium bicarbonate due to the measuring equipment not being read from straight on. This in addition detracts from the accuracy of the experiment. Additionally, the results are only an approximation as rounding occurred during the trigonometry calculations.
The accuracy, reliability and validity of the experiment were weakened due to errors and problems that were encountered during the experiment. As the variable involving the amount of sodium bicarbonate paste could only be changed once, and quite a large number of errors occurring, the experiment is neither reliable nor accurate. The validity of the experiment was additionally affected by this low reliability and accuracy. However, all the variables except the ones being tested were controlled making the experiment reasonably valid.
To improve the accuracy, reliability and validity of this experiment it is important to have multiple trials before the conduction of the experiment to discover which amounts of sodium bicarbonate paste are likely to propel the rocket into the air. Additionally, obtaining an estimate as to when the rocket would launch and taking precautions to prevent inaccuracy in the measurements of the sodium bicarbonate and vinegar would improve the reliability and accuracy of the experiment.
In conclusion it was found that the amount of sodium bicarbonate paste that was added to a vinegar and sodium bicarbonate rocket did have an affect on the height that it was able to reach after being launched. It was additionally found that the rocket was able to reach the greatest height of 7.30 metres with a quarter of a teaspoon of paste, and gained no height with one teaspoon. This proved the hypothesis to be incorrect.
Viewed 25th July 2009; <http://csep10.phys.utk.edu/astr161/lect/history/newton3laws.html>
Viewed 28th July 2009; <http://csiro.au/scope/activities/e04c03actiity.htm>
Viewed 25th July 2009; <http://exploration.grc.nasa.gov/education/rocket/newton.html>
Viewed 30th July 2009; <http://exploration.grc.nasa.gov/education/rocket/newton1r.html>
Viewed 27th July 2009; <http://www.spacesociety.org/spaceexpress/Curriculum/film_canisters.html>
Viewed 25th July 2009; <http://teachertech.rice.edu/Participants/louviere/Newton/>