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

String and tape experiments
Since g is 10 m s-~
(or N/kg), you can check to see if T calculated from the static bending of the
ruler agrees with the dynamic experiment. You can vary the spring constant k by shortening the
part of the ruler which can bend. This experiment is quite important because simple harmonic
motion is such a common phenomenon in physics. The gravitational mass of the marbles bends
the ruler in the first part of the experiment, whereas it is the inertial mass we are using in the
oscillation. Your experiment shows they are proportional.
Velocity and acceleration
A ruler with a channel down its length, a marble and some sticky tape, as shown in figure 4a,
provide all the necessary materials to study velocity and acceleration.
m
Figure 4.
Stick the tape across the groove in the ruler at zero, 7.5, 15 and 22.5 cm. Tilt the ruler so
that, when released from the top, the marble just makes it to the bottom. Now set it going,
and listen to the clicks as the marble drops off each piece of tape and strikes the ruler. The
clicks are always equally spaced in time, however fast you set the marble going with your finger
tip. What does this show? Are the times between clicks the same if one piece of sticky tape is
removed?
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