previous    next

Oscillations

Hooke's law (example)

From the experiment of Walter Lewin we learned the following.
Let the initial length of the spring be .
When Walter Lewin loaded the spring with an object of mass 1 kg, the spring stretched to a length of +u, where u=13 cm.
The spring and the weight were in equilibrium. Hence, the spring excerted an upward force which was equal to the weight of the object (9.8 N).
The extension u of the spring was downward, the elastic force of the spring was upward force.
The elasticity constant is given by

C_el = - F_el /u = - (9.8 N) / (-0.13 m) = 75.4 N/m

Walter Lewin repeated his experiment with loads of 2 kg and 3 kg. He obtained the following result.

C_el = - F_el /u = - (2×9.8 N) / (-2×0.13 m) = 75.4 N/m
and
C_el = - F_el /u = - (3×9.8 N) / (-3×0.13 m) = 75.4 N/m

This confirms that the spring he used was an ideal elastic medium.

Harmonic motion