We have been told that in the absence of all other external forces except gravity, a falling object will accelerate at 9.8 m/s^2 and the purpose for this experiment is to prove that.
The device we used is pictured below. It is said to be 1.5 m high and consists of a powered electromagnet at the top. From top to bottom along the device's body there is a wire which is connected to a spark generator. This will emit a spark, at a constant time interval, as a metal plumb bob falls from the electromagnet. Between the path of the falling plumb bob and the sparking wire a strip of spark-sensitive paper is placed so that every time a spark is generated, a mark is left behind.
We have conducted the experiment at this point and the parks have been collected on the strip of paper. In terms of time each of the spaces are equal, 1/60 second, but this is not the case for the physical distance between each mark. So what we do now is measure as accurately as possible the space between each of the marks as they increase.
The time and displacement were then put into a chart on excel so that we could use them to find the graphs of position vs time and velocity vs time. We can see that the position vs time graph curves which confirms that velocity is changing, increasing in this case. The velocity vs time graph was then plotted and what we got was a linear graph which confirms a constant acceleration. Our acceleration was measured to be 9.38 m/s^2 and although our constant acceleration was not exactly what we were looking for it is what we measured.
Average velocity was calculated using the equation:
v = [x(b)-x(a)] / (1/60)
where
t = [a,b]
The overall class average for acceleration was 9.48 m/s^2.
So why the wrong "answer"?
It's not so much a calculated error but instead an experimental uncertainty. For one, the calibration in the meter stick is not great but rather "good enough" for most things. So how wrong were we?
Relative difference = [(9.48-9.8) / (9.8)] * 100 = -3.26%
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