分类：教育/科学-理工学科-物理学
问题：一道英文物理题Ahelicalspringisplacedupr 
A helical  is placed uprightly on a surface. On the upper end a sphere is placed (but not attached) on the spring. This pendulum has a frequency of f=1.2Hz. Find the maximal amplitude of the pendulum such that the mass just does not lose the contact with the spring.
回答：mg = kA, 

where m is the mass of the sphere, g is the gravitational acceleration, k is the stiffness of the spring,and A is the amplitude of the vibrational system,as the problem says of the pendulum.

A = mg/k = g/(k/m) = g/ω^2,

where ω is the angular frequency of the system,

 ω = sqrt(k/m)= 2 π f,

Thus we have
 A = g/(2πf)^2