New trends in physics teaching, v.4; The ... - unesdoc - Unesco

New Trends in Physics Teaching IV
Figure 2.
Note the period (time for one oscillation), T, goes up as the number of marbles goes up - but
they do not give a straight line if you plot one against the other. If you have no watch, remember
a pendulum, such as a marble, on a string 99.4 cm long has a period of two seconds - each swing
from side to side takes one second. Count the number of oscillations in ten seconds. If you plot
the square of the period versus the number of marbles, however, you get a straight line plot such
as figure 3. The appropriate formula is T = 27rfi where k is the spring constant, the force
required to extend the spring by unif distance, and m is the inertial mass of the marbles. Let us
suppose the spring extends a distance x when you put the marbles in the cup. The force is mg
where g is the acceleration due to gravity (or gravitational field strength) and k = mg/x
40 -
30 -
L
(U
D
E
2
20 -
1 0 - X
I I I
0 1 0 2
T2/S2
Figure 3.
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