Honors Labs

1) Many of you are in danger of getting a zero for the ferryman ( relative motion) lab. Where are they?

2) Most of the harmonic labs have be redone for many reasons.

a) How can you say that the k values were similar or not without showing me the calculations and results for the ks for each of the three parts? You must do these calculations and show them and the results.

b) Many of you plotted deltaL vs Mg for part 1 which is fine. Then k=1/slope. Then you said units of slope were N/m but they are really m/N which makes sense since the slope is 1/k.

c) Many of you found the velocity in part 3 by dividing the xmax by the time from the gate, when the gate recorded how long it took the card to pass through, not how long it took the card to get from xmax to the equilibrium point. You must use vmax = cardheight (or width)/time.

d) You were supposed to use the slope to find k not individual points on the graphs. Use equations we developed as noted below

To find the k values use : part 1 k= 1/ slope ; part 2 k = (2pi)squared/slope part 3: k =m times square of slope .

e) Many of you concocted strange explanations for how a larger mass increased the amplitude and thus led to shorter or longer periods. The mass has nothing to do with the amplitude. The mass determines where the new equilibrium is, but once you let the mass rest there, you are the one who pulls the spring as far as you want to establish the amplitude. You did this several times in parts 3 and 4.

Also, our theory and your data show amplitude does not affect period (see part 4 for instance.) In any case, the mass effects the period in a horizontal oscillator also, so the mass effect on period has nothing to do with the force of gravity. It has to do with inertia, resistance to acceleration. Omega goes as the square root of the restoring acceleration per meter of displacement. The acceleration is inversely proportional to the mass, therefore omega is proportional to the square root of 1/mass. Since T is inversely proportional to omega, T is proportional to the square root of mass.

f) some of you decided that despite part 4 data to the contrary, T depends on amplitude. Don't let your preconceived notions over rule data so easily.

g) For the post lab some of you lost track of units. Remember 1 g = .0001kg and 1 cm = .01m

h) Also in the post lab, many of you went through entire calculations to come up with the new mass ( question 4)= .4015 kg. It doesn't. Since m1 = .1 and T2 = 2 x T1 and T is proportional to square root of mass then m2 must be exactly = 4 x m1. You don't need a calculator, or even a calculation for this.