Unit 4 sec 5.1
summarising a set of scientific measurements
13 January 2016
23:09
Gravity on the Earth’s surface is the downward force exerted
on an object by the mass of the Earth. The size of this force varies slightly
at different parts of the earth, in particular at different altitudes and
latitudes. When an object is dropped, and that no other forces, except gravity
are acting on it, it’s speed increases at a constant rate as it falls to the
ground. At sea level, this speed increases by approximately 9.81m/s every
second. This increase in the speed each second is now as the acceleration due
to gravity, and it is denoted by the letter g. In SI units, g is measured in meters
per second per second, which is written as m/s², so g= 9.81m/s².
A group of
experiments tried 2 measure g, based on the following 2 different methods:
ª
Free fall, where a ball bearing is dropped, and
the time taken for rate to fall through a known height is measured.
ª
Pendulum, where period of swing of the pendulum
(which is affected by the strength of gravity) is timed.
An interesting question arising out of this experiment is:
which of these 2 methods give the better estimate for g? You are asked to
investigate this, using the data that the experiment collected.
At 1st
glance, you may have noticed that there are some subtle variations in the measured
of values of g. These variations are not necessarily associated with any
geographical differences in g; we can assume that each experiment to place in
the same location, so in theory the results should all be the same. In, the
differences that we of the serve in the data can be ascribed to what is known
as experimental error. Statistical analyses of repeated measurements, such as
calculating the mean of the dataset of repeated trials is an important method
for minimising the effects of experimental error in scientific experiments.
2 features stand
out from these summaries
in terms of location, the averages (i.e. mean and median) of
the free fall data wipe closer to the truth value for g of 9.81m/s², then do
the pendulum averages.
In terms of spread,
there is a much narrower spread for the freefall than for the pendulum data is
calculated by any of the measures.
So, on the evidence of these summaries, the freefall
experiment produced better results, since the average of the experimental
values is closer to the true value of the results were more closely clustered
together.
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