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I will firstly set up a clamp stand with a piece of string 50cm long
attached to it.
- A mass of 50g will be attached securely to the end of the string
The mass will be held to one side at an angle of 45 degrees (measured
with a protractor), and then released.
- A stop watch will be used to time taken for one full oscillation
This will be repeated a number of times, each time shortening the
length of string by 10cm
- The length of the pendulum will be plotted against the period on a
graph.
NB. The final length of string and mass will be decided after my preliminary
investigation.
Apparatus
- Meter ruler
- Protractor
- Clamp stand
- Clamp
- Stop watch
- String
- Mass
Diagram
The following factors will be considered when providing a fair test:
The mass will be a constant of 50g throughout the experiment
- Angle of amplitude shall be a constant of 45 degrees. This will ensure
that there is no variation of the forces acting on the pendulum.
- The value of gravitational field strength will inevitably remain constant,
helping me to provide a fair test.
- The intervals between the string lengths will increase by 10cm each
time. This will help me to identify a clear pattern in my results.
- If any anomalous results are identified, readings will be repeated. This
will ensure that all readings are sufficiently accurate.
- To ensure that the velocity is not affected, I will ensure that there are no
obstructions to the swing of the pendulum.
The following factors will be considered when providing a safe test:
- Care will be taken not to let the bob come into contact with anything
whilst swinging the pendulum, as the weight is relatively heavy (50g)
- The clamp stand will be firmly secured to the bench with a G-clamp so
that the clamp stand will not move, affecting the results.
Excessively large swings will be avoided (angle of amplitude will be 45
degrees
Results of preliminary investigation
My preliminary investigation was successful. I learned from my preliminary investigation that my proposed method might not give me sufficiently accurate results. These results may be inaccurate dueto a slight error of measurement in time, height or length.. I will take three readings of each value during my final experiment and take an average. I will also measure the time taken for 5 oscillations rather that 1 and then divide the result by 5. These two changes will hopefully help me to identify and eliminate anomalies, sshould they occur. They should also add to the accuracy of my results.
Obtaining Evidence
I used the method proposed in my plan, taking three readings of each value
and measuring the time taken for 5 oscillations rather than for 1. During the
experiment, I observed that each oscillation for the same length of string
seemed to be equal. This showed that the pendulum did not slow down as the
number of oscillations increased. I took the safety measures described in my
original plan.
During the experiment I was careful to use accurate measurements in order to
obtain sufficiently accurate results, for example:
- The string was measured with a meter ruler, to the nearest mm, to
ensure that each measurement had a difference of exactly 10cm.
- The angle of amplitude will be measured with a protractor to the
nearest degree to ensure that the angle remains constant throughout
the experiment.
- A stopwatch will be used to measure the period accurately. The period
was measured in seconds, with the stopwatch measuring to the degree
of two decimal places of a second. However, I have rounded up each
time to the nearest second to give appropriate results.
- The mass was measured using five10g masses, to ensure that the mass
remained constant throughout the experiment.
Results:
Length of string (cm) Period (secs)
50 7.2
8.1
6.45
40 6.25
6.6
6.4
30 5.6
5.2
6.15
20 4.55
4.5
4.6
10 2.95
3.25
3.0
I took three readings of each value and took an average for each concentration.
I then divided by 5 to get the average reading for one oscillation. This again
should influence the accuracy of my results.
Table of averages:
Length of string (cm) Period (secs)
50 1.45
40 1.28
30 1.13
20 0.91
10 0.61
Using the formula, T = 2 L
g
found in the Scientific Theory, I calculated the perfect results that should have
been obtained, had my experiment followed the formula exactly:
Length of string (cm) Period (secs)_
50 1.44
40 1.25
30 1.07
20 0.91
10 0.64
Using my averaged results, I squared P to show the relationship between P
and L:
Length of string (cm) Period (secs)_
50 2.1
40 1.64
30 1.28
20 0.83
10 0.37
As all my results were accurate, I had no need to repeat any of them. However,
had there been an anomalous result, or had I come across any problems, I
would have repeated my results to identify the cause and eliminate anomalies.
Analysing evidence and concluding
Using the results from my table, I drew a graph to show what had been
obtained from the experiment (see graph A). The graph clearly shows a
smooth curve with a positive gradient. This indicates that as the length of the
pendulum is increased, the period will increase.
Although my second graph (see graph B), does not show a perfect straight line
through the origin, a line of best fit can be drawn to show this. This backs up
the theory in my scientific knowledge, that P is directly proportional to L,
i.e. if the length of string was doubled, the period would be doubled.
My table of results drawn from my experiment was extremely similar to the
results produced from the scientific formula, showing that my experiment was
successful. My two graphs showed resemblance to my predicted graphs,
indicating that my results were sufficiently accurate and therefore, my
proposed method was reliable for this experiment.
My findings indicate that the time period varies directly with the length of the
string when all other factors remain constant.
Evaluating
The evidence obtained from my experiment supported my prediction that as
the length of the pendulum increases, the period increases. This is also shown
in Graph A, as the graph displays a smooth curve with a positive gradient. My
method in squaring P was successful, as I discovered that T was directly
proportional to L, providing all other values remain constant. This was shown
by a straight line going through the origin (Graph B). These results were
encouraging and led me to believe that my proposed method was sufficient for
the experiment.
Some of the results were not accurate, as they did not match the results
produced by the formula. This could have been due to human error. However,
the majority of my results were no more than a decimal place away from the
formula results and, therefore, quite reliable. Had there been any anomalous
results, I would have repeated my readings.
Factors which may have affected the accuracy of my results include:
- Error in measurement of angle of altitude. This angle proved difficult to
measure and it was hard to get the exact same angle for each result. To
improve the accuracy of this measurement, I could have attached the
protractor to the clamp stand so that it was in a fixed position.
- Error in measurement of string. To improve the accuracy of this, I
could have marked off the points with a pen to ensure they were as
accurately measured as possible.
- Human reaction time. Depending on human reaction time, the
measurement period time could have been measured inaccurately, due
to slow reactions when setting the stopwatch etc. This could have been
improved by involving another person to aid me with my experiment,
for a quicker reaction time.
The procedure was relatively reliable, excluding human error, and so I can
conclude that my evidence is sufficient to support a firm conclusion that:
The only factor which affects the period of a simple pendulum is its
length. As the length increases, so does the period.
If I were to extend my investigation, I would investigate to provide additional
evidence to back up my conclusion, for example, changing the mass or angle
of altitude. The results gained would hopefully aid me further in supporting
my Scientific Theory. It would also be interesting to investigate how the
factors are affected when the Gravitational Field Strength is different, i.e.. not
9.8 Newton’s.
