Calculating Spring Constant - Force or Energy?

by Cintdrix
Tags: spring, spring constant
Cintdrix is offline
Nov12-09, 10:44 AM
P: 4
I've been being confused lately as to the 2 methods. The example I'm thinking of is when a weight of mass m is hung on a spring and it stretches x meters.

First of all, I know you can equate the spring force (kx) to the force of gravity (mg), to get
k = mg/x

But is it also possible to say that the gravitational potential energy lost (mgx) is equal to the energy gained by the spring (1/2 kx^2)? When I do this, I get a different k which is half the original k and probably wrong. How can you calculate K for this problem using energy?
Phys.Org News Partner Physics news on
Physicists consider implications of recent revelations about the universe's first light
Vacuum ultraviolet lamp of the future created in Japan
Grasp of SQUIDs dynamics facilitates eavesdropping
dsol is offline
Nov12-09, 12:08 PM
P: 5
The first method F = mg = kx is what you would use to find the spring constant k. The second equation is used for the dynamic problem "How fast is the mass moving at distance x?". To solve, equate the potential energy "lost" by the downward motion to the potential energy of the spring AND the kinetic energy of the object: E = mgx = (1/2 kx^2) + (1/2 mv^2)

Register to reply

Related Discussions
stretching of a spring: calculate force constant of spring in terms of distance and m Introductory Physics Homework 6
Force of spring constant Introductory Physics Homework 1
k; the force constant of a spring Introductory Physics Homework 15
Calculating a force constant using kinetic and potential energy? Introductory Physics Homework 0