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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