An Oscillating Straw

8/6/2019 An Oscillating Straw

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A . B . P a t e r s o n C o l l e g e

Y e a r 1 1

P h y s i c s

2 / 2 4 / 2 0 1 1

Year 11 Physics

By Chi Ho Ng

An Oscillating

Straw



Introduction

The aim of the experiment is to investigate how the length of the pendulum affects the period of its

oscillation in relation to the acceleration of free fall. Using a straw filled with sand in a pendulum

position, along with timers and other equipment.

Define variables:

Constant: length of straw (L)

Independent variables: distance from the middle of straw (h)

Dependent variables: time taken to complete one period (T)

Unknowns: acceleration of free fall (g)

Method1. Measure the length of the straw

2. Mark the midpoint of the straw with a pen using a ruler with the level of uncertainty to

+ or 0.5 mm

3. At 30mm away from the midpoint, push the pin through at an right angle to the straw

4. Measure and record the distance h (in m m) between the pin and midpoint by using a

ruler with the level of uncertainty to + or 0.5 mm

5. Set up retort stand and other equipment as shown in the diagram

6. Let the straw hang off the pin by making both pins take the same shared weight of the

straw to be more accurate

7. Let it stable and use a protractor to a measure 10 degrees angle from its equilibrium

point from the top end of the straw

8. When let go use a timer to time how long it takes for the straw to complete five

complete periods and record time in the results table

9. Repeat step 7 and 8 three times and take an average to minimize the error

10. Change the h value to 40mm and repeat step 7, 8 and 9



Additional notes to minimise the parallax errors: repeat the test to average out the

abnormalities.

Risk assessment

Risk Prevention

Injuries by needles Use it sensible and dont leave it unattended

Sand in eye Dont put it above your eyes

Dropping retort stand on foot Dont put it on the edge of the table/bench



Equipment

y Cork

y Straw

y Pinsy Sand

y Blue tack

y Ruler

y Timer

y Retort stand

y Data recording table

y Protractor

Diagram

Hand drawn set up of the retort s tand and other equipment



Photos

Basic set up of the experiment

Zoomed in on the straw

Results

Independent variable: L, H

Dependent variable: T

Data table:L/mm L

2 /mm H/mm H

2 /mm T1 /sec T2 /sec T3 /sec Average /sec T1 osci /sec T1 osci

2 /sec

224 50176 30 900 4.49 4.21 4.4 4.36 0.87 0.76

224 50176 35 1225 4.03 3.95 3.9 3.96 0.79 0.62

224 50176 40 1600 3.67 3.84 3.53 3.68 0.73 0.54



224 50176 45 2025 3.57 3.34 3.49 3.46 0.69 0.48

224 50176 50 2500 3.36 3.45 3.27 3.36 0.67 0.45

Data set 2

Data collected using a protractor, therefore a constant angle

Analysis

Table used to create the table:

x y

900 14.72

1225 15.24

1600 16.58

2025 19.36

These data are used to produce a graph because the oscillating straw obeys this equation:

. The data plotted out appears to be linear and though regression it

is, so therefore a linear equation will be used to find the unknowns, (g).

is the standard form for linear equations, to find the unknown (g) using a linear

approach will require the oscillating straws equation to be in a general linear equation format.

Therefore:

L/mm L2 /mm H/mm H

2 /mm T1 /sec T2 /sec T3 /sec Average /sec T1 osci /sec T1 osci /sec

2

224 50176 30 900 3.34 3.62 3.55 3.50 0.70 0.49

224 50176 35 1225 3.23 3.37 3.3 3.3 0.66 0.43

224 50176 40 1600 3.1 3.29 3.27 3.22 0.64 0.41

224 50176 45 2025 3.22 3.28 3.34 3.28 0.65 0.43

224 50176 50 2500 3.25 3.32 3.13 3.23 0.64 0.41



Where

Using this method the unknown (g) would be found, by finding the gradient and substituting and

rearranging the equation to g

and also by finding the y intercept and substituting in and

and rearrange the equation to

. Then two (g) values would be obtained and it will

be averaged to min the error.

Working

The linear equation for the graph:

Y intercept= 11

From gradient g=7.01

From y intercept g=7.29

Average =7.15

Second method of finding (g)-less accurate

The flowing way of determining (g) is only using the existing points other than using the more

accurate method of using the points from the line of best fit/ model.

The oscillating straw obeys this equation:

To find (g) the equation is rearranged to make (g) the subject:

Sub data from h`=30 into equation to find g

Sub data from l=35 into equation to find g






Now an average would be taken to minimise the error

C

onclusion In conclusion, the g value is calculated to be around 7.15m/sec^2 and 9.72m/s^2. It is noticed that

as the (h) value increases the time taken to complete one oscillation increases due the weight of the

straw which gravity is acted apon. The graph is linear; this is shown by regression on the data and by

just looking at the changing y over changing x.This experiment shows that when a pendulum is

displaced, gravity will pull it toward it equilibrium with the acceleration of gravity which is 9.81. Due

to error in the data collection it is close to the actual value but it wasnt exact. The data from the first



attempt was shown to be not so accurate when the graph was plotted. Therefore it was only used to

test another method of the experiment, but in the end it was actually closer to the actual value. This

might be because the answer from the first method to find g was averaged so many times but the

second wasnt so there is a greater error in the second method. This could be more accurate if the

gradient and y intercept was not found by hand.

Evaluation

The accuracy of the data is only limited to a 2 significant figures as this is the lowest of all the

measurement taken. The uncertainty (line of worse fit line of best fit over line of best fit times by

100) of the graph is 48.7%. The uncertainty thought the measurement is + or 0.5mm or + or 0.15

sec. the final uncertainty is around 55% and it is very high due to the errors involved. The most

unreliable data was the human error involved in the timer when timing the periods of the pendulum,

also the ruler used to measure how far to swing back limits to data s accuracy to only plus or minus

0.5mm. The human error can be reduced by filming the experiment and use programs to analysis the

swings.

It is suggested that a video could be taken on each test and to be analysed by the program Logger

Pro which will give a very accurate reading of the pendulums motions. This will reduce the human

error greatly because it does not require a humans reaction to correctly stop the stop watch.

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An Oscillating Straw

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