Stretching Springs and Making Graphs

We want to study the relationship between the force pulling on a spring and the amount the spring stretches.  Clearly, the more we pull, the more it stretches, but how much more?

Part I:  Taking Data

Measure the mass of the weight holder and spring.  Replace the spring on its support and record the location of the pointer or the bottom of the holder (or any other point you can locate consistently).  Gradually add mass to the holder, thus increasing the force stretching the spring.  For each amount of mass, record the location of your reference point.  Take about 10 data points, but do not put more than 200 grams on the holder.  As you read the locations, record your data to the nearest half millimeter.  That is, if the reading is exactly on the 4.4 line record it as 4.40 cm.  If you would estimate the location to be 4.44, then record it as 4.45.   4.48 would be recorded as 4.50.  I think this is the best we can do for accuracy with the this equipment.

Part II: Analyzing the Data

For each amount of mass calculate the amount the spring is stretched from its original position.  Also, calculate the force on the spring. (Don't forget to count the mass of the holder and spring.)  Plot a graph of Stretch versus Force.  Is the graph a straight line?  If so, draw in a best fit line and find the equation of the line.  If not, see your instructor.  Using your equation for the line, find the spring constant (k) for your spring.  Does the line have a nonzero y-intercept?  If so, what could have lead to this occurring?