Exp 9-1 P
Experiment 9. Spring Constant
-Is rubber more elastic than steel?
The answer lies in the concept of elasticity.
Objective:
To determine the spring constant of a spring by
(a) static method, and (b) dynamic method.
Apparatus:
A spring, a hanger with a light aluminium pointer, a small scale etched
on a plane mirror strip, weights, a timer.
Theory:
(a) Static method:
Consider a spring hanging from a rigid
support. When a load m is suspended from
the free end of the spring, an external, Fext,
acts on the spring in the downward direction.
The support applies an equal force in the
upward direction. Thus the spring has a Spring
balanced system of forces acting on it and it
is in equilibrium. . The length of the string
-increases and an internal (restoring) force
Fi nt is developed in the spring due to the
elasticity of the spring. This internal force
tends to bring the spring back to its original
length when the external forces are
withdrawn. Note that Fint and Fext are
equal in magnitude.
According to Hooke's law,
Fi nt is directly proportional to x, the
change in the length of the spring. Mirror
Thus Fint=-kx (1)
Here k is the constant of proportionality,
known as the spring constant or force
constant. The minus (-) sign indicates that
Fint and x are in opposite directions.
Obviously,
Fext=kx.
Eqs. (1) and (2) indicate that the sprin ,g constant k
to the force required to change the length of the spring
(2)
is numerically equal
by 1 unit.
