# Physics 109 - Hooke's Law

This experiment is a chance to refresh your skills from last term, including:

•  estimating uncertainty
•  propagating uncertainty in a calculation
•  plotting graphs in a spreadsheet program
•  using minimization of chi-squared to find a best-fit line

PART I

As a review of last term, work in groups of 4, on the boards or on large paper sheets, and sketch a flow diagram that ilustrates the steps that you gor through when doing an experiment.

PART II

After we discuss the flowcharts, regroup to discuss why we do these things when trying an experiment. Write these reasons in your lab notebook.

PART III - Uncertainty Problem (work in pairs)

The following problem will help you with an uncertainty calculation needed in the experiment below.
Consider a situation where you have measured a distance of 1.55 cm on an analog scale with 0.1 cm divisions. You decide that the maximum value it could possibly be is 1.60 cm and the minimum is 1.50 cm.
What do you report as the uncertainty?

Next consider a similar measurement  of 2.75 cm, with the same uncertainty, and you need to subtract these two distances. What is the difference in the distances? What is the uncertainty in the difference after you do this subtraction?

PART IV

Hooke's Law is a description of an ideal spring that says the stretch in the spring is linearly related to the force applied : F = kx, where k is called the spring constant.

In MKS, what are the units of k?

Using the apparatus at your desk provide a very high-quality measurement of the spring constant using Hooke's Law. (Hint: Your measurements of distance should be taken more precisely that just to the nearest mm.)Your final result should include a graph of stretch versus mass with a best fit line that goes through the origin, a plot of residuals from the fit, and your best estimate of the value of the spring constant in SI units. Remember to record which spring set-up you use, since you will want to use the same one for another experiment later.

Marking Scheme

2 marks flow chart participation, and an explanation in your notebook

2 marks for uncertainty problem

10 marks for a high quality determination of the spring constant
don't forget to: