99 Orange Rocket

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99 Orange Rocket Balloons

16/12/2011 § 1 Comment

Research Question & Overview

The research question for this experiment is “Determine the work done and the power of a

balloon rocket.” We have assumed that the rocket balloons in this experiment generally

exert an average thrust force of 0.5N but we know that that is actually not the real

average thrust force.

Background Information

The units we used for this experiment were work, energy and power. Work is the action of

a force to cause displacement of an object and is represented by J , joules. It can be found

by multiplying force (N) by the distance traveled, or displacement (m). The equation to

find work is therefore Work (J) = force (N) x displacement (m) .

Energy is the ability to do work and is almost identical to work. Different types of energy

include kinetic, mechanical, elastic, potential, thermal, sound, and others. Both energy

and work are found the same way (with the same equation) and energy is represented also

by J , joules. The equation for energy is thereforeEnergy (J) = force (N) x displacement (m) .

In context, however, work is the actual displacement of an object and energy is the

object‟s ability (actual and potential) to be able to move and “do work”.

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Power is the rate of doing work or using energy. Power is the relationship of work (energy)

and time. It is basically how fast or how slow an object can do work. Power is represented

in W , watts, where 1 watt is equal to 1 joule in 1 second. Once the value of work/energy (J)

is known, simply divide the time (seconds) to find the power. The equation to find power

is therefore Power (W) = work done or energy used (J) ÷ time (s) .

At the beginning of the run, the forces that were acting on the balloon rocket were thrust,

air resistance, normal force and gravity. While the normal force and gravity cancel out,

friction and air are acting against the direction of the balloon. At the initial release of the

rocket, the balloon exerts a lot of energy and releases lots of air. Because of this, the

thrust force is strong; stronger than friction from the string and air resistance combined.

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Towards the end of the run, the amount of friction and air resistance stays about the

same. Air resistance could have changed because the shape of the balloon has changed

and the surface area doesn‟t hit as much air. By now, though, the rocket has lost most of

its air and doesn‟t have as much thrust as it did in the beginning of the run. This is seen

in the arrow that points right (the direction of the balloon rocket). It is smaller than it was

in the previous diagram.

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In the reaction force pair, the elastic of the balloon presses against the air as it runs

across the string. On the snapshot of the diagram drawn, as the rocket heads left, the

elastic also moves that direction. The line demonstrating the air‟s direction (pointing

right) shows that air pushes against the elastic surface of the balloon.

The first law of thermodynamics is the law of conservation of energy . This means

that energy is neither created nor destroyed. It can be transferred from one object to

another or tr nsforme from one form to another (Taylor, 2011). When the balloon is

blown up with the air inside it, it hold potential elastic energy because the elastic of the

balloon will tend to lose all tension to try to go back to its original, floppy shape. Also

when the balloon is blown up (not many people may notice or remember this), there is

also thermal energy transferred into the balloon which could be felt because the

temperature of the balloon‟s rubber went from its typical cold temperature to a warmer

temperature. This thermal energy probably comes from the air that is blown into the

balloon and is transferred into the balloon‟s rubber material. When the balloon is released

along the string, most of that potential energy is transformed into kinetic energy and this

is seen in the thrust that pushes the balloon one way. The rest of the energy is

transformed into thermal energy, elastic energy and sound that isn‟t used in the work

done by the rocket.

Method & Video

My group (which consisted of me, Kyu Jin and Alisa) created a method that would be the

most efficient in that it gathered multiple units and types of data as quickly as possible.

Below is the video of our method with a few notes of details we paid attention to, along

with who in our group did what job.



The method was very simple, structured and efficient. We all knew our jobs (stated in the

video at around 0:33 – 0:40), which made things easier. Basically, after we tied up a long

length of rope on a railing and taped up the other end on a column, I blew up the balloon

(Alisa would help me determine if each balloon was approximately the same size as the

previous balloons) and released it. We didn‟t bother un-taping the balloon from it‟s spot

on the straw and the string as that would have taken a lot of time. Instead, I blew the

balloon from where it was on the string. Alisa used her iPhone to time each run. We took

about 6 to 8 runs and out of that, chose the clearest ones. Kyu Jin helped measuring (also

seen in the video) by using his fingers as a marker to indicate where to put the meter

stick. We measured where the straw‟s end started and where it finished (refer to video).

Processing the data collected by this method simply consisted of letting Excel do all the

math and using iMovie to process the videos from the iPhone to find out how many

seconds each run took.

Variables

There was no independent variable in this experiment, nothing that we could manipulate

to see its effect on a dependent variable. The variables that we did measure

were work and power . (To find these, we found measurements for distance and time.)

There were multiple controlled variables in the experiment. These were the slope of the

string that the balloon rocket ran along, the amount of air that is in the balloon, and

the tension of the string . An uncontrolled variable in the experiment is how much air is

released as soon as the balloon is let go.

The above stated controlled variables were controlled while setting up the experiment and

while doing the experiment. The slope of the string, for example, was manipulated by

having someone adjust the string according to what the other group members roughly

estimated was exactly 90˚ to the column. The amount of air that was in the balloon was

controlled by me and Alisa mostly, where I‟d blow the balloon but we‟d both estimate,



based on the size of the balloon, if there was the same amount of air in the balloon as in

previous runs. Finally, the tension of the string was easily controlled simply by pulling the

string tight and not letting it flop about. By making sure the string‟s tension was very

strong, we could be sure that the rocket balloon would run across the string smoothly

without having to struggle because of a string that was loose and that wasn‟t tense

enough.

Data Collection and Processing

The results gathered from this experiment generally tried to stay within a certain range of

measurements. These measurements are, for distance (in meters), about 6.70 meters to 7

– 8 meters (precisely 7.75 meters). This range is about one meter (1.02 meters, to be

exact), which is actually a long distance because one meter is rather far. The

measurements for time (in seconds) range from 1.8 seconds to 2.5 seconds, which isn‟t

even a full second. The relationship that we see in data is that, generally, the longer the

rocket balloon travels (even a few extra deciseconds), the further it is displaced from its

starting point on the line. The

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data does not totally

support this, however, because if we arrange the values for time in ascending order (see

table to the right), we can see that the time and distance don‟t gradually grow together.

Balloons 1 and 3 do ascend in terms of time, but descend in terms of distance traveled.

The same situation occurs with balloons 2 and 4. The time increases by 0.1 seconds but

the distance does not increase. Instead, it decreases by about 0.065 meters. In general,

though, the most basic pattern is that the time travelled and the distance travelled are

interlinked together in each rocket balloon run. This is because, logically, the longer

amount of time something moves at whatever speed, the more distance it covers.

The error for the measurements for distance is 0.05 meters, which is also 5 centimeters. I

gave the error bar for distance two decimals because we had Kyu Jin stand next to where

the balloon would end and each time, he‟d make sure that we‟d measure to almost exactly

where the balloon ended. The method we used was just precise like that. The error bar I

used for the measurements of time was 0.2 seconds because I think it‟s fitting enough. In

iMovie, I was able to stretch each clip out and see each ½ second but iMovie also enables

me to see things in 0.1 seconds so whenever I stop somewhere within the clip, it‟s usually

quite accurate.

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I processed the data we already collected in order to find the work and power of each

rocket balloon. The table below („Calculated work and power for balloons 1 – 5‟) depict

these calculations. The calculations used were the ones previously given in

the Background Information section. We can see that in general, the amount of work

(joules) that the balloons are doing ranges from within 3 to 4 joules. The calculated power

for the balloon rockets in general ranged in between 1.50 watts to about 1.90 watts (1.87

watts, to be exact, see Balloon 1). Of all the balloons, this means that balloon 1 used the

most power during it‟s run. This makes sense because balloon 1, although it had one of

the shorter displacement measurements, took the least time out of the five balloons. This

means that it took more power for the balloon to get from the start to the end of its run in

a shorter period of time while the other balloons had a little bit more time to run the

length of their displacement. The error for the measurements of work and power were

each 0.5 (joules and watts, respectively). This gives the data some breathing space just in

case the measurements are a little off but it doesn‟t try to be too exact either because our

measurements are very raw and probably not exact as they could be with proper materials

and more time.

Above is the collection of averages of all five rocket balloon runs of distance, time,

work and power. According to the table, the average distance traveled was 7.11 meters

but we have to remember to look back at the actual raw data. If we look at balloon 5, we‟ll

see that it‟s a bit of an outlier compared to the other balloons at 7.75 meters, whereas the

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closest measurement next to balloon 5 is balloon 2, which is only at 7.38 meters. Also,

balloon 3 is also a bit of an outlier as it is equally as separated from the middle three

balloons as balloon 5 is. The time, work, and power averages are as stated, 2.22 seconds,

3.55 joules, and 1.61 watts.

Qualitative Data

One of the rocket balloon runs that we were about to film failed terribly because as soon

as I released the balloon, the rubber stuck onto the concrete of the column and just stuck

there for about half a second before actually running along the string. This reminded us

that we had to make sure that the rocket was free of all disturbances before letting it go.

Additionally, the length of the string limited the experiment a bit because we realised if

the amount of air in the balloon passed a certain point, the rocket would just hit the end

of the string (which happened to be a rail), bounce back along the string, and be a useless

run. Finally, the string would move a lot along with the rocket.

Reliability and Validity of the Data

The data probably could have been more reliable than it actually seems. In fact, although

our method was very consistent (if you refer back to the video, our way of measuring each

balloon‟s run was methodical and consistent; each member did the exact same thing each

time which adds to the reliability of the method, therefore the reliability of the data

gathered through that method). The raw measurements are reliable and quite valid but

afterwards, the calculated work and power may not be as valid and reliable. The factor

that most impacts the consistency and accuracy of the collected data is the amount of air

that was used during each run. Since we couldn‟t accurately measure an exactly amount of

air for each time we blew the balloon up, the amount inside the balloon was definitely

different for each separate run. Since the amount of air is the factor that affects most how

far the balloon will travel and how long it will travel for, this is the primary reason why all



the gathered data (distance, time, work, and power), although we tried to measure

everything as precisely as possible, isn‟t wholly and as reliable and valid as it could be.

Conclusion

Efficiency is a percentage or a ratio to show the useful work out of the total amount of

work done (Taylor, 2011). The equation to find efficiency is therefore: Useful work out (J)

÷ total work done (J) x 100% . In this case, the balloons are not being efficient because of

where the energy is being transferred and what the original potential energy is being

transformed into. The work done by these balloons is their displacement on the string

so efficiency would mean a lot of energy, or as much energy as possible, put into the

movement of the balloon. We know that good amount of the balloon‟s original potential

elastic energy is not transferred into the kinetic energy (the movement) of the rocket.

Most of it goes to sound, elastic energy and thermal energy.

We also know that the rocket faces a few barriers on its run, more so at the end than in

the beginning. This cuts down on the energy because it takes more energy to pass these

barriers. During the entire run, the rocket has to deal with friction from the string that we

used to hang the straw from. The friction is greater at the end of the run when the thrust

force of the balloon isn‟t enough to overpower it. At the beginning of the run, however,

there was a lot of initial thrust that propelled the balloon to move forward with lots of

energy. That energy eventually dies down, which causes the balloon to also slow down

because not enough thrust can move it forward. At the same time, there is also air

resistance because of the size of the balloon. It‟s elastic surface area, as shown in the

reaction-force pair in theBackground Information section, is what hits the air as the rocket

runs along the string. Newton‟s 3rd law of physics is that “Every action has an equal and



opposite reaction” and this law applies to this balloon experiment (Stern, 2004). This

pushes against the forward movement of the balloon and if there was not as much air

resistance, the rocket would have traveled further. All these factors add up to precipitate a

less than 100% efficiency.

There are multiple ways to increase the efficiency of this rocket machine. The objectives

are to obviously tackle the factors that take away from the efficiency of the rocket, like the

ones previously explained.

1. One method to increase the rocket machine‟s efficiency and decrease the areas where

energy is lost to different transformations is to reduce the air resistance that pushes

against the balloon‟s elastic surface area. A simple way to reduce the amount of air

resistance on the balloon is the decrease the balloon‟s surface area. There are multiple

examples of how a smaller surface area makes movement faster. Planes and jets can cut

through the sky and not find too much trouble with the colossal amount of air resistance

they face at the speeds they travel because planes are quite thin. Similarly, skis and

snowboards, when running down slopes, are quick because they are flat and the only area

that is hitting air resistance is the front edge of each ski or the front edge of the

snowboard. Just as well, if a swimmer makes sure that their bodies are straight in the

water and as straight as line as possible, they will surely cut through the water a lot

quicker. This is similar to the way the balloon should cut through the air. There are many

thin balloons (that clowns use to make animals) that we could use for the experiment

instead of big fat party balloons.

2. A second possibility is to reduce the friction from the string and on the straw. The string

that we used for this experiment was like cotton and had little hairs sticking out, which

probably added to the friction that hit the straw. An easy fix to this type of string is to

simply use better string to hang the machine from. These strings could be plastic wiring

that can be found almost anywhere, as long as we use something that will not cause a lot



of friction. At the same time, we can also make reduce friction by manipulating the straw.

If we lubricate the inside of the straw that slides along the string with oil, honey or some

kind of liquid that isn‟t too thick or too watery, then the movement of the straw along the

string will be very easy.

3. Finally, we can transfer and manipulate the distribution of sound and elastic energy (the

flapping part of the balloon) at the opening of the balloon. If we can manipulate both

these types of energies, we can successfully transfer the energies to contribute to the

thrust of the rocket, therefore the movement of the rocket. We can do this by inserting

another straw into the mouth of the balloon and taping the outsides. Taping the outsides

of the opening will control the flapping of balloon‟s mouth and greatly reduce

unnecessary energy transformation that will instead go to directing the balloon to moving

one way. The flapping originally changed the direction of the rocket (the balloon only

went one direction because it was stuck to a string) and was really trying to move the

balloon in multiple directions and angles. This is why when you randomly release a

balloon, it flies all over the place and doesn‟t head in one direction. If the mouth is

controlled and doesn‟t flap all over the place, the direction will also be controlled and the

movement of the rocket won‟t be disrupted by forces trying to push it to go different

directions. Also, by taping a straw into the mouth, the air will come out a lot more

smoothly and there won‟t be that ridiculous sound that comes from the mouth when a

balloon is released. Without this sound, more energy can again be put into the thrust of

the balloon which can push it further.

1. Additionally, (as a bonus), putting a straw into the inside of the balloon will actually force

use to different means of pumping air into the balloon. It will definitely be harder to blow

air into the balloon if there is a straw taped into it during the entire experiment but if we

use small bike pumps (which do exist), we could actually increase the accuracy of the

experiment. This can be done, for example, by keeping track, of how many pumps of air

you put through the straw.



In general, if we make sure to decrease the barriers that the rocket faces and redirect the

transfer of energy to types of energy that will help the work done by the machine, we can

be able to increase the efficiency of the machine.

Extended Conclusions

We assumed that the balloon‟s force while it ran along the string was 0.5N but we also

knew that this measurement was wrong. After retrieving the actual information about the

balloon‟s mass, I was able to calculate the actual work and power of each balloon run and

the actual average work and power.

I was able to calculate the actual information after finding the actual mass at 3 grams. If I

convert this to kilograms, it would be 0.003kg. Afterwards, to find the force of an object

of that mass, I‟d multiply it by 10N. The actual thrust force of the balloon is therefore

actually 0.03N. I was able to plug this value in to calculate for work and then use my

previous information (of the total time of each run) to find the power. The values are

shown above, along with the respective calculated averages next to the originally

calculated average to compare with.

If we compare the average that we‟ve calculated now (0.21 joules and 0.1 watts for work

and power respectively), the difference is drastic and each value is far from the original

averages (3.55 joules and 1.61 watts for work and power respectively). The drastic

difference in the averages are proof that the assumed force was invalid, very off and

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inaccurate. This can also been seen in the fact that 0.5N and (the real force) 0.03N are

also quite far from each other.

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