# Homework Help: Spring distance vs force lab question

1. Oct 19, 2008

### proace360

1. The problem statement, all variables and given/known data
In our lab, we had springs of different tolerances hung off of a holder (I can't really describe it) by one end and dangled different masses on the other end. We had to put the data that we collected of displacement and force on a graph and find the linear best fit line.

On one of the analysis questions, it asked what the value of the y-intercept described and why, and our values were between .5 and 1.5 for the different strings. With a y-int, that means that when the distance is zero there is a force acting on the spring. We assumed that it was the weight force, but the teacher said that it wasn't and it was some other "thing". I don't know what that thing is and I was wondering you could help me. I understand that the slope is the k value, but what does the y-int mean?

they were like force=27.5(distance)+.819 or something like that

2. Relevant equations

f=kx

3. The attempt at a solution
In the wall of text

2. Oct 19, 2008

### proace360

Still no one can help me :(?

3. Oct 19, 2008

### Staff: Mentor

If no force stretched the spring, what would the distance measurement mean?

4. Oct 19, 2008

### proace360

Well, the distance is on the x-axis and the force is on the y, so the question is what having no distance but still having a force means

5. Oct 19, 2008

### Staff: Mentor

Right. I asked you the opposite question: When the force is zero, what does the distance measurement mean?

6. Oct 19, 2008

### proace360

Oh, well if the force is zero, than the distance measurement is the displacement the spring experiences with no force acting on it.

7. Oct 19, 2008

### Staff: Mentor

Well, yeah... But what does that mean?

When you measured "distance", what did you actually measure? The displacement measured from what point?

8. Oct 19, 2008

### Staff: Mentor

If you're still drawing a blank on my question, here's another version: If you remove the applied force on the spring, why isn't the displacement zero?

9. Oct 19, 2008

### proace360

Well, I thought it was due to the the weight of the spring, but my teacher said that that was wrong. I have no clue why it wouldn't be zero any other way.

10. Oct 19, 2008

### Staff: Mentor

Did you take into consideration the unstretched length of the spring?

11. Oct 19, 2008

### proace360

well, we took the initial measurement of the string from while it was hanging to eliminate weight as a force acting on the spring (since it would be constant). I'm confused by what you mean with unstretched length because we weren't required to take that measurement.

12. Oct 19, 2008

### Staff: Mentor

When you say you measured displacement, what did you actually measure? Displacement from what? If you hung the spring without any weights on it, does that count as zero displacement? When you hung a weight, did you measure the additional displacement from the position it had when no weight was hung?

Since I don't have the details of what you actually did, I can only guess. (A diagram would help if you had one.)

13. Oct 19, 2008

### proace360

I'll see if I can make one

EDIT: Here we go. What we did was measure the initial length of th spring like this, then added a weight, measured the length of the spring, and subtracted initial from the new length for the dsiplacement.

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14. Oct 19, 2008

### proace360

Yes, with no additional weight to the spring would be zero displacement. When more weight was hung, we measured the length of the spring and subtracted the original additional-weightless length for the displacement.