Spring constant calculation (help needed)
Author
i got stucked on a question...hope someone here can help me out..
a 254mm long, 3kg/mm compression spring is now cut till 178mm long, wat will be the new spring constant/stiffness in (kg/mm)?
is this calculation cotrrect?:
K1 X length 1 = K2 X length 2
hence,
K2 = (length 1/length 2) X K1
= (254mm/178mm) X 3kg/mm
= (4.28kg/mm)
thanks in advance
Quote:Original post by Eelco
kg/mm,wht kind of unit is that, btw?
kilograms per millimetre...
which seem strange for a spring constant. I would expected Newtons per unit length.
-Josh
Author
kg/mm is not an SI unit....just a given unit.
actually shud change to Newton/meter
btw....if the calculation is correct...
like
K1 X length 1 = K2 X length 2
let's say u compress spring 1 for a length of "length 1" (it's own length, tht means u compress it fully, though it's not legical to do so, just assume it can be done).
u will need F1 = K1 X length 1 = 4.4kg/mm X 254mm =1117.6 Kg.
since K1 X length1 = K2 X length 2
which gives us F1 = F2
which also mean, we need F2 = F1 = 1117.6kg aswell, to compress the short spring fully?
so no matter how we cut a spring, we still need the same force to compress it fully???
since F1 = F2 = F3 = F4.........
is tht true?
and i would like to know how to calculate the spring constant using
given spring diameter
given spring coil diameter
given turns/wounds per unit length
given length
given modulus of elasticity of material used
thx again
[Edited by - TauhuTauhu on August 30, 2005 5:32:06 AM]
actually shud change to Newton/meter
btw....if the calculation is correct...
like
K1 X length 1 = K2 X length 2
let's say u compress spring 1 for a length of "length 1" (it's own length, tht means u compress it fully, though it's not legical to do so, just assume it can be done).
u will need F1 = K1 X length 1 = 4.4kg/mm X 254mm =1117.6 Kg.
since K1 X length1 = K2 X length 2
which gives us F1 = F2
which also mean, we need F2 = F1 = 1117.6kg aswell, to compress the short spring fully?
so no matter how we cut a spring, we still need the same force to compress it fully???
since F1 = F2 = F3 = F4.........
is tht true?
and i would like to know how to calculate the spring constant using
given spring diameter
given spring coil diameter
given turns/wounds per unit length
given length
given modulus of elasticity of material used
thx again
[Edited by - TauhuTauhu on August 30, 2005 5:32:06 AM]
Quote:Original post by jjd
which seem strange for a spring constant. I would expected Newtons per unit length.
Maybe not so odd, in a sense. I can imagine it is convenient to factor out graviational acceleration, however, I think the final units should be equivalent to Newtons per unit length.
-Josh
Quote:Original post by jjdQuote:Original post by jjd
which seem strange for a spring constant. I would expected Newtons per unit length.
Maybe not so odd, in a sense. I can imagine it is convenient to factor out graviational acceleration, however, I think the final units should be equivalent to Newtons per unit length.
-Josh
meh, what about springs on the moon? springs loaded by other factors than gravity? kg is not a measure of force. period.
Quote:Original post by TauhuTauhu
kg/mm is not an SI unit....just a given unit.
actually shud change to Newton/meter
btw....if the calculation is correct...
like
K1 X length 1 = K2 X length 2
let's say u compress spring 1 for a length of "length 1" (it's own length, tht means u compress is fully, though it's not legical to do so, just assume it can be done).
u will need F1 = K1 X length 1 = 4.4kg/mm X 254mm =1117.6 Kg.
since K1 X length1 = K2 X length 2
which gives us F1 = F2
which also mean, we need F2 = F1 = 1117.6kg aswell, to compress the short spring fully?
so no matter how we cut a spring, we still need the same force to compress it fully???
since F1 = F2 = F3 = F4.........
is tht true?
yes. the force it exerts depends on the deformation. just picture a spring, exerting a load F, and then picture the two virtual halves of it: they both also exert this same force F, and the same goes for any subsection of that same spring.
Quote:
and i would like to know how to calculate the spring constant using
given spring diameter
given spring coil diameter
given turns/wounds per unit length
given length
given modulus of elasticity of material used
thx again
ill think about it.
ignoring any moments induced in the spring (only sheer):
K = G * crossection / (2Pi*r * (turns/m) * L)
G being the sheer modulus, which you can calculate given E and nu.
r is the radius of the whole spring, crosssection the crossectional area of one wind of the spring as cut though from the direction of loading.
K = G * crossection / (2Pi*r * (turns/m) * L)
G being the sheer modulus, which you can calculate given E and nu.
r is the radius of the whole spring, crosssection the crossectional area of one wind of the spring as cut though from the direction of loading.
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