# Formula for combined spring constant.

1. Apr 18, 2005

### nerfed

Help - Formula for combined spring constant.

Hey, I was wondering if anyone can help me with the formula to calculate the combined spring constant of two springs stuck together (end to end).

This is as far as I've been able to figure it out lol, I can't wrap my head around this formula. The k1 and x1 are the values of the first spring, and k2 and x2 are the values of the second spring respectively.

F(series) = [(k1)*(k2)] * [(x1)+(x2)]

Last edited: Apr 18, 2005
2. Apr 18, 2005

### Staff: Mentor

Not sure what that formula means. (The units don't make sense!)

Hint: Realize that two springs in series must have the same tension.

3. Apr 18, 2005

### nerfed

Heh, yeah, that's why I need the help.

I need to know how to find the spring constant of two springs connected end to end. That botched equation up there is my attempt at it, so I was wondering if you guys knew it.

4. Apr 18, 2005

### Staff: Mentor

You should be able to figure it out with the hint I gave. Use your same notation:
$$T = k_1 x_1 = k_2 x_2$$

But the tension is also given by:
$$T = k_{series} (x_1 + x_2)$$

Play around with these and see what you can do.

5. Apr 18, 2005

### jdavel

nerfed,

Here's another hint. If you have a spring with spring constant k and you cut it in two, what are the spring constants (call them k1 and k2) of the two pieces?