Investigating factors which affect the period time of a simple pendulum.
Investigating factors hich affect the period time of a simple pendulum
Investigating factors which affect the period time of a simple
pendulum
Planning
Definitions: Oscillation : Repeated motion of pendulum (to and for)
Period (T) : Time taken for one full oscillation
In this investigation, I am going to experimentally determine a factor which
will affect the period of a simple pendulum and the mathematical relationship
of this factor. This type of pendulum will consist of a mass hanging on a length
of string.
Factors which affect the period (T) of a pendulum:
- Length (L) of pendulum
- Angle of amplitude
- Gravitational field strength (g)
- Mass of bob
I predict that the period will be affected by the length of the pendulum. An
increase in length will produce an increase in time. I based by prediction on
the scientific theory I found in a physics text book:
The pendulum is able to work when the bob is raised to an angle larger than
the point at which it is vertically suspended at rest. By raising the bob, the
pendulum gains Gravitation Potential Energy or GPE, as in being raised, it is
held above this point of natural suspension and so therefore is acting against
the natural gravitational force. Once the bob is released, this gravitational
force is able to act on it, thus moving it downwards towards its original
hanging point. We can say therefore, that as it is released, the GPE is
converted into Kinetic Energy (KE) needed for the pendulum to swing. Once
the bob returns to its original point of suspension, the GPE has been totally
converted into KE, causing the bob to continue moving past its pivot point and
up to a height equidistant from its pivot as its starting point.
The same factors affect the pendulum on its reverse swing. GPE gained after
reaching its highest point in its swing, is converted into KE needed for it to
return back to its natural point of vertical suspension. Due to this continuous
motion, the bob creates an arc shaped swing. The movement of the pendulum
is repeated until an external force acts on it, causing it to cease in movement.
The pendulum never looses any energy, it is simply converted from one form
to another and back again.
I am therefore going to experimentally determine the relationship between the
length of the pendulum and the period.
In the scientific theory, I found a formula relating the length of the pendulum
to the period. It stated that:
P = 2 L
g
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motion, the bob creates an arc shaped swing. The movement of the pendulum
is repeated until an external force acts on it, causing it to cease in movement.
The pendulum never looses any energy, it is simply converted from one form
to another and back again.
I am therefore going to experimentally determine the relationship between the
length of the pendulum and the period.
In the scientific theory, I found a formula relating the length of the pendulum
to the period. It stated that:
P = 2 L
g
P = The period
g = Gravitational Field Strength
L = Length of string
This formula shows that L is the only variable that when altered will affect the
value of P, as all the other values are constants.
The formula: P = 2 L
g
can be rearranged to produce the formula: P = 4 L
g
and therefore: P = 4
L g
As 4 and g are both constants, this means that P must be directly
proportional to L.
I can now say that the length of the pendulum does have an affect on the
period, and as the length of the pendulum increases, the length of the period
will also increase.
I will draw a graph of P against L. As they are directly proportional to each
other, the predicted graph should show a straight line through the origin:
Method
- I will firstly set up a clamp stand with a piece of string 10cm 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 (measured
with a protractor), and then released.
- A stop clock will be used to time taken for 10 full oscillation
- This will be repeated 3 times, each time shortening the
length of string by 10cm
NB. The final length of string will be 10cm investigation
Apparatus:
- Meter ruler
- Protractor
- Clamp stand
- G-clamp
- Stop clock
- 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.
- 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:
Length of string (cm) Period (secs)
My investigation was successful. The results from my table back
up my prediction that, as the length of the pendulum increases, the period
increases.
I learned from my preliminary investigation that my proposed method may
not give me sufficiently accurate results. These results may be inaccurate due
to a slight error of measurement in time, height or length. Although this
experiment produced no anomalies, I will take three readings of each value
during my final experiment and take an average. I will also measure the time
taken for 3 oscillations rather that 1 and then divide the result by 3. These
two changes will hopefully help me to identify and eliminate anomalies,
should 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 3 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 stop clock will be used to measure the period accurately. The period
was measured in seconds, with the stop clock 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.
Results:
Length of string (cm) Period (secs)
I took three readings of each value and took an average for each concentration.
I then divided by 3 to get the average reading for one oscillation. This again
should influence the accuracy of my results.
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.
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.
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.
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 was successful.
Some of the results were not accurate, 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 stop-clock 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.
Rabar Bek 26/04/2007
