Defining the problem
k is the independent variable and h is the dependent variable
keep the mass of the object constant
Methods of data collection
Set-up the equipment as shown in the diagram.
Fix a rod using a boss at the near top of a retort stand.
Tie the elastic cord on the rod, The other end to be tied at the hook of the hanging mass.
Fix a ruler with its 0 mark at the same level as the top fixed end of cord using clips or clamps.
Fix an electromagnet so that the end of the nail is at the same level as the fixed end of the cord and the 0 mark of ruler.This is needed to ensure that the starting point is the same throughout the experiment.
Measure the mass m using a weighing scale.
To determine the spring constant k of each cord,
hang a few weights, one at a time,
determine the corresponding extensions by subtracting the original length L from the length after a weight is hanged, and
plot a graph of weight against extension and determine the gradient
The gradient is the k of a cord
For each cord with its spring constant k already determined,
tie the mass m previously selected, then measure the length L between the two ends
release the mass m from the upper fixed end [the ruler’s 0 mark] of the cord
measure h or maximum distance fallen by the object using the ruler
Method of analysis
Plot a graph of (h - L)2 / h against 1/ k
To determine g
calculate the gradient of the graph
use this gradient to determine g
g = gradient / 2m
The relationship is valid if the graph is
a straight line
passing through the origin.
Additional detail
When releasing or dropping the mass, use safety goggles. Place a sand bag directly below the dropping so that it catches the mass m thereby protecting the investigator and the floor.
Use cords that
are elastic but, with the assumed hanging mass m, will not hit the floor or the surface of the table where the experiment is being done. Do trials first.
obey Hooke’s Law, that is, with the hanging mass m chosen, it will not reach its elastic limit.
The retort stand is usually vertical. In case unsure, check using a set square.
For each cord, repeat the experiment several times, then determine the average h.
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