Posted by **Kriti** on Thursday, March 17, 2011 at 12:15am.

I'm making a graph of force vs stretch for springs. I have 7 data trials with the k (F = kx) ranging from 28 to 31, average is 29.6.

Now I need to find the slope and write an equation for the graph. If I use the first two points to get the slope, I get a slope of 29.4. If I use the first point and the last point, I get a slope of 28. I understand the larger interval would give the best value, but using the first two points to compute it gives a slope closer to my "k" value. I know the slope is my spring constand or k value so they should be close.

Question is: which interval should I use: first and second points or first and last points to compute the slope.

- physics -
**drwls**, Thursday, March 17, 2011 at 12:22am
You should use all three and minimize the square error when fitting a straight line through the origin.

It's called a linear regression best fit.

This will also give you an error estimate.

- physics -
**kriti**, Thursday, March 17, 2011 at 12:31am
So my slope doesn't have to be so exact to the k value?

When I use the equation to predict the stretch, I get a value of .085 using the first two points and a value of .089 when using the first and last points. The given data table lists the actual stretch at 0.085.

So in showing my work, which 2 points should I use?

- physics -
**drwls**, Thursday, March 17, 2011 at 6:30am
You should use all seven of your data points, and a linear regression curve-fitting technique. There are tools online at places like

http://people.hofstra.edu/Stefan_Waner/RealWorld/newgraph/regressionframes.html

## Answer This Question

## Related Questions

- physics - in a making a graph showing the stretch of a spring: Plot a graph of ...
- Math - I need help with this questions. a). An overhead garage door has two ...
- physics - 1)If I am to plot a graph of Force in Newtons vs. Stretch in meters, ...
- Physics - The figure below shows two springs connected in parallel. This ...
- Physics - The figure below shows two springs connected in parallel. This ...
- Physics - The innerspring mattress on your grand- motherâ€™s bed is held up by 23 ...
- biology - Data Table: Rate of Photosynthesis Trial # Number of Bubbles/Minute 1 ...
- physics - sorry mr bob pursley to annoy you again. i read over hooke's law in ...
- Physics Lab - I'm doing a lab on centripetal force but I'm not sure how to make ...
- Physics - Now consider the same two springs in series. 6.4 N/cm, 3.6 N/cm 44 N ...

More Related Questions