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A Design investigation for International Baccalaureate (IB) Physics HL.
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NAVRACHANA INTERNATIONAL SCHOOL VADODARA
GROUP 4 EXPERIMENTAL SCIENCES
PHYSICS HL
STUDENT LABORATORY REPORT
Name of the student: Harshil Patel
Candidate number : 002605-030
Examination session: May 2012
Date of investigation: 1st December 2012
Internal Assessment Criteria: Design
Supervisors Name: Mary Chacko
Title: Decent time of the Parachute
Candidate Name: Harshil Patel Candidate Number: 002605-030
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Parachute Investigation
Title: Observations on the decent time of the Parachute
Topic: Mechanics
Background: Parachute is a device designed to reduce the decent time of a body in
atmosphere, by providing drag. Drag is a force which resists the motion of an object through
a fluid. In a parachute drag is created when the air fills the canopy of the parachute.
Parachutes are of utmost importance in flooded areas to drop food packages and for other
recreational purposes. Various shapes and sizes of parachute are designed to serve different
purposes.
Research Question: How does changing the shape of the parachute affect its decent time, if
the height of releasing the parachutes and the surface area of the parachutes is kept constant?
Hypothesis: It is predicted that for varying shapes of the canopy of the parachute, there
would be a significant change in the timings of the fall of the two parachutes. This is because
different shapes have different drag coefficients; therefore, the force of drag is proportional to
the drag coefficient and the relationship between these two can be given by the formula:
Where
Candidate Name: Harshil Patel Candidate Number: 002605-030
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Variables:
Independent Shape of the canopy of the Parachute
How was it manipulated?
First, a circular shaped parachute is designed. Then, calculations
regarding surface areas are made to find the dimensions of a
rectangular (ram-air) parachute. A rectangular (ram-air) parachute
is then designed such that the surface areas of both the parachutes
are same. These parachutes are then used to investigate the
dependent variable. The investigation involves the parachutes to
be released from a constant height of several meters and recording
their decent time
Dependent Decent time of the parachute
How was it recorded?
The stopwatch is checked for zero offset error. Then, the time
taken for the trial falls is recorded using a stopwatch (which has
an uncertainty of 0.01s) to reduce the effect of reaction time. The
stopwatch is started as soon as the parachute is released and
stopped when it just reaches the floor. The fall should timed by
two students. One person should be asked to time the fall by
standing on top of the terrace and other on the ground (where the
parachute landed.) The two timings are then recorded in the data
table. It should be made sure that the timings are recorded by the
same two people to avoid any human error associated with the
persons reflexes.
Candidate Name: Harshil Patel Candidate Number: 002605-030
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Controlled Variable Surface Area of the canopy
Mass hung.
The height of releasing the parachute.
Length of strings.
Material of the parachute.
Area in which the investigation is carried out.
How were they controlled? The dimensions and surface area of the circular
parachutes canopy are calculated, and keeping the
surface area constant, the second parachutes (ram-air)
canopy is designed.
Calibrated masses of 0.1 kg are hung to each of the
parachutes. The whole system, i.e. the parachute and
the mass should weigh about 0.165kg. If it does not,
clay could be added to increase the mass.
The height of releasing the parachutes is measured
using a graduated measuring tape. Both the parachutes
are released from the same height, hence keeping it
constant.
10 inextensible strings of 25cm each are cut out from
the thread roll.
A synthetic cloth is used to make the canopies of the
parachutes.
An ideal place with minimum wind and maximum
height is selected to carry out the trials and the whole
investigation was performed here.
How would they affect the
results if they were not
controlled?
If the surface areas of the canopies re not controlled,
the force of drag created would vary significantly and
hence results would be ambiguous. The formula
(where A is the
frontal/surface area of the parachute) illustrates this
relationship.
Candidate Name: Harshil Patel Candidate Number: 002605-030
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If unequal masses are used, the downward force
would vary and would influence the results.
If the height of release is changed, the distances the
parachutes travel will vary which will in turn affect the
decent time.
Different materials trap air and create drag uniquely.
This is due to the difference in spaces between
individual threads which constitute the material,
allowing for the air to be cut differently. If different
materials are used, the results obtained will not be
reliable and comparable.
If different lengths of strings are used for a parachute,
it would result in instability of the parachute, and hence
the parachute will tremble down its path, giving
inaccurate readings.
If the trials are taken in different places, it is very likely
to affect the path of the parachute. E.g. in windy places,
the parachute would be blown away by the wind.
Apparatus Uncertainty
A synthetic cloth roll of 2m x 2m
1 Compass
1 Scissors/cutters
1 Cello tape
Inextensible nylon thread roll
10 Broom sticks
2 0.1kg calibrated mass g
1 Punching machine
2 Digital Stopwatch s
1 Metre rule cm
A digital balance g
Clay
Candidate Name: Harshil Patel Candidate Number: 002605-030
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Procedure:
1. A place with low wind speed and a considerably high altitude is selected. (This
investigation was performed on the terrace of the school building.)
2. Using a measuring tape, measure the height of the releasing the parachute.
In the laboratory:
3. On a digital balance, press Tare button and wait till the display reads 0.000g.
4. Weigh the calibrated masses on the digital balance to ensure they are of g
(i.e. 0.1kg).
For the circular parachute:
5. With the help of a compass, draw a 0.25 m (i.e. 25 cm) circle on a synthetic cloth and
cut it out with a pair of scissors.
6. Punch eight equally spaced holes (near the circumference) on the cloth (See Diagram
1).
7. Cut eight strings of 0.27 m from the nylon thread roll and tie them to the punched
holes.
8. Tie the free ends of the strings to a calibrated mass of 0.1 kg.
9. Ensure, by measuring with a meter rule, that the lengths of strings from the knots at
holes to the knots on the calibrated mass is 0.25m.
10. Reset the stopwatches and check for zero error.
11. Release the parachute. Simultaneously start the stopwatches. When the parachute hit
the ground, stop the stopwatches. Record the timings by the two stopwatches in the
data table. (See Diagram 4)
Candidate Name: Harshil Patel Candidate Number: 002605-030
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12. Repeat Step 10 and 11 nine times.
Calculations:
The circular canopied parachute has a radius:
m
Surface area of the circular canopy:
( *
+)
m2
NOTE: The surface area of both the parachutes should be constant. Therefore the dimensions
for rectangle (ram-air) parachute are:
Surface area of rectangular (ram-air) parachute:
Diagram 1: Canopy of Circular
Parachute
Diagram 1: Canopy of Circular
Parachute
Candidate Name: Harshil Patel Candidate Number: 002605-030
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m
For the Rectangular Parachute:
1. Cut out a 0.72 m x 0.27 m of rectangular cloth from the synthetic cloth. The edges
should be made to be rounded edges, so as to make the parachute a ram-air type
parachute (See Diagram 2 and 3).
2. Glue the thin broom sticks to the parachutes edges.
3. Punch the holes on the positions marked red on Diagram 2.
4. Cut out eight strings of 0.27 m from the nylon thread roll and tie them to the punched
holes.
5. Tie the free ends of the strings to a calibrated mass of 0.1kg.
6. Ensure, by measuring with a meter rule, that the lengths of strings from the knots at
holes to the knots on the calibrated mass is 0.25 m.
7. Check both the stopwatches for zero error.
8. Release the parachutes from a constant height and simultaneously start the
stopwatches (See Diagram 4). When the parachute hits the ground, stop the
stopwatches and record the timings in the data table.
9. Repeat Step 7 and 8 nine times.
Candidate Name: Harshil Patel Candidate Number: 002605-030
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Diagram:
Diagram 3
(taken from http://www.armedforces-
int.com/suppliers/jpads-parachutes.html 12/02/12)
Diagram 3
(taken from http://www.armedforces-
int.com/suppliers/jpads-parachutes.html 12/02/12)
Diagram 2: Canopy of Rectangular
Parachute
Diagram 2: Canopy of Rectangular
Parachute
Diagram 4 Diagram 4
Candidate Name: Harshil Patel Candidate Number: 002605-030
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Explanations:
The holes were carefully punched so as to keep the parachute sturdy and not allowing
it to collapse inside.
The broom sticks provided a skeleton for the parachute not allowing it to collapse.
Data Table
Processed Data Table:
Circular Parachute
Trial # Timings/s 0.21 s
Stopwatch 1 Stopwatch 2
1
2
3
4
5
6
7
8
9
10
Rectangular (ram-air) Parachute
Trial # Timings/s 0.21s
Stopwatch 1 Stopwatch 2
1
2
3
4
5
6
7
8
9
10
Circular Parachute
Trial # Average time of two
stopwatches/s 0.21 s
1
2
3
4
5
6
7
8
9
10
Rectangular (ram-air) Parachute
Trial # Average time of two
stopwatches/s 0.21s
1
2
3
4
5
6
7
8
9
10
Candidate Name: Harshil Patel Candidate Number: 002605-030
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