Spring Mass System Approximations questions

[Ethers0n]

I have been trying to figure out why it's considered a "good" approximation in spring mass calculations to add 1/3 of the mass of the spring to the total mass of the system. I understand the need to add SOME extra mass (other than the mass of the weight added to the bottom of the spring for example) but do not understand why specifically that amount is needed. I've thought about air friction losses and losses internal to the spring, but have still come up with nothing. Any help would be appreciated.

Thanks

[chroot]

Please do not post your question to more than one forum at a time.

- Warren

[Ethers0n]

sorry about that...

I didn't realize there was a specific area just for homework questions. I reposted here after I realized where the parent post should have been.