Year 8 – Science Assessment #4
Aim
The aim of this experiment is to show the effect of using different types of string on the
velocity of a balloon rocket.
Hypothesis
If Newton’s laws of motion states that where thrust is generated by pressure, then it can be
assumed that a balloon rocket will be propelled down the line of a string as it is the air
moving backward that causes the reaction of the balloon to move forward. If the balloon
rocket is tested with twine (thick), yarn (medium thick) or fishing wire (thin/smooth) , then
the velocity of the rocket will be affected as friction is introduced through the different
string type compositions and the straw.
Predictions:
The results would be expected to reflect that with the balloon rocket will slow down or
speed up travelling on the different types of strings as in their thickness and material
composition. There are different types of friction involved per different types of string and
the straw which affects the balloon rocket’s motion as there is more resistance working
against the balloon travelling forward along the string.
Friction occurs when two objects are rubbing against each other and as a result it tends to
slow the momentum of the objects involved. Rough surfaces cause more friction and slow
things down than smooth ones. Scientist believe this is the result of the electromagnetic
attraction between charge particles in two touching surfaces.
The expectant results should reflect that the balloon will travel faster on the fishing wire
followed by the yarn and the slowest speed to be recorded will be for the twine. The fishing
wire is smooth and fine with less friction qualities to the two other alternatives with the
twine being a thick/bulky compared to the yarn which is medium/thick in nature.
Source A: https://ksmyth0522.commons.hwdsb.on.ca/2013/04/19/73/ - diagram showing
how frictional qualities of string affect the movement of the balloon rocket.
With consideration to Newton’s Third Law of Motion which states for every action, there is
an equal and opposite reaction. The gas rushing out of the balloon is the action and the
movement of the object in the opposite direction is the reaction. If a body exerts a force on
a second body, then the second body exerts a force that is equal in magnitude and opposite
in direction to the first force. No force occurs by itself. As the balloon pushes the air out,
the air pushes right back on the balloon with an equal and opposite force. The air goes back
and the balloon goes forward. The more air there is inside the balloon, then the longer it
will be able to push with that force and more momentum the rocket will achieve. To sum up
all these actions and reactions are happening because of force, air, pressure, push and
thrust.
Source B: https://promotiontablecovers.blogspot.com/2019/04/balloon-rocket-experimentworksheet.html // Diagram showing Newton’s Third Law of Motion.
Source C: https://kirthank.wordpress.com/2011/12/15/balloon-rockets-lab/
Diagram showing forces acting on the balloon when the balloon is just let go.
Source D:
https://swift.sonoma.edu/education/newton/newtonsLaws/newton_3/thirdLaw.htm picture demonstrating balloon rocket experiment with consideration to Newton’s Third Law
of Motion.
Variables:
Independent variable:
Type of string:
Twine– thick/ rough
Yarn – smooth
Fishing wire -fine/smooth
Dependent variable:
Velocity – in order to compare velocities, I need to measure the distance and the time that
the balloon rocket travels on the straw of each different type of string.
Control :
3 breaths deposited into the balloon per trial
balloon size
straw type (same diameter/same material)
same string length for each string material tested
same chairs
placement of the string between the same type chairs on the same flooring with no altering
to the angle of the string – must be in a straight line
string must remain taut in this experiment
Equipment:
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1 balloon
1 paper straw (24cm) – diameter (0.6mm) remains the same and length remains the
same throughout the experiment
String – 3 pieces – 1 single strand of twine (rough texture ) /1 single strand of yarn
(medium texture) / 1 single strand of fishing wire (fine/smooth texture) – 6m each in
length
Scissors
Tape measure
Stop watch
2 chairs placed opposite ends of each other with a distance of 5.5m between them
Cello tape
Masking tape
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2 people – 1 to do the timing and measuring and the other to position and blow the
balloon up
Paper
Pen
Method:
1.
2.
3.
4.
5.
6.
Gather equipment.
Using tape measure – measure each piece of string to the length of 6m.
Cut excess from string and discard.
Feed the straw through the first string type – the twine.
Secure one piece of the string to the top of the first chair frame with masking tape.
To begin first trial, secure the other end of the first string type to exactly the same
position on top of the second chair frame with masking tape – a distance of 5.5m is
required between each chair end.
7. Measure the distance between the chairs so that when string is taut, the distance of
the string measures 5.5m in length in total.
8. Gather cello tape and cut into sections of 5cm in length using scissors – you will need
two pieces of these for the experiment.
9. Secure these two pieces on top of the straw with a distance of 5 cm apart between
each piece of cello tape, preferably closer to the middle of the straw. Make sure to
leave equal distance from the ends of the straw.
10. Position one’s body right next to the first chair while making sure the straw is in
alignment to your body.
11. Blow up the balloon with 3 full breaths.
12. Position the balloon underneath the paper straw secured by the two pieces of cello
tape.
13. Hold balloon without letting the air out – do not tie shut.
14. Secure the balloon containing air to the tape which is secured on the straw.
15. Position the balloon rocket in a starting position which is near first chair.
16. Release the balloon and start the stopwatch
17. Stop the time when the rocket reaches its limit.
18. Using tape measure, measure the end the point that It reached when it was
released. Record measurement in data table.
19. Record the time in seconds in the data table.
20. Repeat for two more additional trials and record results per string type.
21. Calculate the average time for three trials per string type.
22. Record average time and average distance in data table per string type.
23. Calculate and record the average velocity using the formula v=d/t
Distance= distance in meters (5.5m) divided by t-average time
24. Repeat the above procedure (steps 4-23) using other string types.
Risk assessment:
Risk
Balloons over inflated can pop.
Balloons can be a choking hazard to
children and pets.
Scissors can cause cutting injury.
Balloon materials can cause allergic
reactions to those people who have
allergies to latex.
Control
Be mindful of the amount of air put into
balloon. As recommended in this
experiment no more than 3 breaths to be
deposited in balloon.
Do not leave balloon or packet of balloons
unattended.
Do not leave scissors unattended.
If individual suffers latex allergy use an
alternative such as mylar.
Results:
Data/Observations/Calculations:
String Type Distance (m) Time (s)
Trial 1
Time (s)
Trial 2
Time (s)
Trial 3
Average
Time (s)
Velocity
(m/s)
Twine
5.5 meters
1.64
1.70
1.82
1.72
3.20
Yarn
5.5 meters
1.62
1.54
1.11
1.43
3.85
Fishing Wire 5.5 meters
2.11
1.69
1.84
1.88
2.93
Average time = Trial 1 = Trial 2 = Trial 3
3
Velocity = Distance
Average Time
Discussion:
The results indicate that the balloon rocket travelled faster along the fishing wire compared
to the other two string types used in this experiment. The balloon rocket travelling on the
fishing wire recorded the fastest velocity speed of 2.93 (m/s) followed by the twine string
3.20 (m/s) and the slowest velocity speed was for the yarn with a speed of 3.85 (m/s).
These results do support my design for my experiment demonstrating how a variable such
as altering a string type can affect the velocity of an object but not all the velocity speeds
recorded are reflective of my initial thoughts.
The experiment was designed to test the balloon travelling along 3 different types of string;
twine (thick), yarn (medium) and wire (thin) and the effects of the different types of string
and whether they would either slow down or speeding up the balloons velocity. In order to
compare velocities, I had to measure the distance the balloon rocket travelled down the
predetermined string length and the time it went the distance. This information allowed me
to use the formulae v=d/t (velocity = distance divided by time ) to calculate and compare
the velocities of three different strings.
In my predictions, I did speculate that the balloon travelling on the fishing wire would have
a faster velocity due to less friction between the string and the straw as it is smooth, fine
and has less frictional attributes compared to the others in the trial. After 3 trials of each
string type, my prediciton was proven correct for the fishing wire as it gave me a result with
the velocity for it being 2.93 (m/s )while the other two string types showed velocity that
reflected to be a slower pace.
What is interesting is that the yarn produce a faster velocity compared to the twine which in
my initial predictions was not what I speculated. I predicted the balloon would have a
faster velocity with the yarn compared to the twine. I was incorrect. The twine is very
rough and not nearly as smooth as the yarn or fishing wire. In this case it can be agreed
there is a lot more resistance in play with the balloon rocket and straw. The yarn is
smoother and finer than the twine but not to the extent of the fishing wire which is the
smoothest and finest type I am using in this experiment. My results do reflect truth in my
hypothesis that a balloon’s velocity is affected by friction as this is reflected in the results I
achieved for the fishing wire compared to the other two string types. To substantiate my
claims surrounding the other string types and their predicted velocity speeds, I need to do
further investigating into this matter. In order to do this, I need to repeat the entire
experiment with particular attention to the twine and yarn part of the experiment while still
keeping most of the control variables in place but with some adjustments. These are
further discussed below.
Reliability:
The experiment was repeated three times per string type and I assumed that I would have
got an expectant result consistent with my prediction but I did not. I did not take into
consideration that that different manufacturers of balloons use different materials. I lost
the 2 balloons contained in the science experiment pack early on in the experiment
following the first three trials of the twine. I resorted to a different manufacturer of balloons
while presuming they were the same shape, fabric and having the same air reserve. This
may explain why my results differed for the twine compared to the yarn as I changed
balloon manufacturer in this time frame. The yarn and the fishing wire were supported by
the new manufacturer in my experiment. If I had used the same manufacturer of the
balloons consistently through the whole experiment then I feel would have succeeded in my
predictions.
Regardless of the balloon manufacturer, my experiment was reliable in that it gave me the
result I expected for the balloon rocket velocity being faster on the fishing wire compared to
the other two materials.
The amount of air in the balloon also needs further discussion as this was not measurable
but just based on the lung capacity of the individual filling the balloon each time. The
individual concerned did tire during the experiment so I can assume that perhaps not the
same amount of air was been deposited consistently during this experiment. Furthermore,
the balloons elasticity would have been affected by the constant air going into it through
the trial periods which again would not make this experiment not so reliable. Perhaps to
overcome this crucial part of the experiment, then a regulator of hydrogen with a reliable
gauge would have been able to dictate the consistent amount of air in the balloon per trial.
Accuracy:
The experimental results do show that friction is one factor that can affect the velocity of an
object. I clearly identified this with the fishing wire trial and I was able to match the
expected values. The accuracy of the other two string types is arguable and not reflective of
my predictions. The experiment needs to be repeated with a number of factors altered
namely consistency with the balloon type and a reliable measure of the air going into the
balloon which I believe may have also affected the results I was trying to achieve.
Validity:
In this experiment it was hard to keep the balloon types the same. The science pack
supplied only two balloons but in reality I needed a stronger balloon to use through the
whole experiment or a pack of balloons supplied from the same manufacturer for me to
use. I do believe if I was able to redo the test with the balloon type being the same
throughout the experiment, as well as being able to gauge and consistently put the same
amount of air in the balloon, I would have achieved a result consistent to my predictions.
Further discussion on this experiment may also involve using a new balloon from the same
manufacturer per string type trial which would eradicate the elasticity factor of the balloon
in reliability of this experiment but this would have to be noted in the control section of the
experiment as a consideration. I do believe this would add greater accuracy to my
experiment.
Conclusion:
The results for this experiment do prove that friction is a factor affecting velocity of an
object. The results for the fishing wire support my hypothesis that a rocket balloons velocity
is affected by friction. It’s velocity was faster 2.93 (m/s )compared to the other two strings
supplied.
Appendix:
Table reflecting total balloon rocket results :
String Type
Trial
Distance
travelled
over 5.5m
(m)
Average
Distance (m)
Time
travelled
over 5.5m
(s)
Average
Time (s
Twine
1
2
3
2.43
2.07
3.50
2.67
1.64
1.70
1.82
1.72
Yarn
1
2
3
5.10
3.02
3.40
3.84
1.62
1.54
1.11
1.43
Fishing Wire
1
2
3
3.99
5.18
5.03
4.74
2.11
1.69
1.84
1.88
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