Week 9 Lab Data

Groups 5 and 6 worked with the Nick model, which leveraged gravity to cut a stone lying on the ground, using a bronze blade. The blade was essentially a sector of an annulus, with radius 17cm, and an arc length of 49cm and 40cm. The first stone we tried to cut was an 11cm by 31cm by 22cm slab, cutting along the longest edge. The main problem with this was that the stone was too big to fit under the blade without bringing the pendulum saw back to the shop and fixing it, so we instead tried to cut a thinner, trapezoidal slab, with the bases being 30cm and 44.5cm, a height of 23cm, and a thickness of 8 cm. Even in this case, we had to use wood chips to raise the pendulum (these would have to be periodically adjusted as we used the saw). We attempted to chisel a groove into the stone to start, but struggled and decided to try it without. We started trying to cut this stone at 2:15. This entailed two people with ropes pulling the saw back and forth while others poured water and emory on the cut. However, we ultimately were unable to stay in the groove. Summarized below are the various things we tried to fix it.

Time	Attempted solution
2:24	Added tape to the pendulum to keep it from sliding back and forth; this also helped keep the wood chips in place.
2:30	Changed how we were holding the ropes so the tension counteracted horizontal motion
2:43	Added a bucket of sand (weight of 6440g) to the pendulum to weight it down
2:56	Worked on doing small cuts

Ultimately, it was the last solution (and Jake’s guidance) that helped us realize our folly. In order to keep it stable, we needed to use small cuts to keep it in the groove, which is very hard when the cut is quite small. While everything we did was helpful, this made us decided to start over with a new stone, and to take the time to chisel out a good starting groove.

The new stone was 2.5 cm by 30cm by 30cm, and we started cutting it at 3:14 along the diagonal. Immediately, we achieved better results, and by 3:55, we had reduced the depth by 0.6cm, 1cm at 4:18, and 1 cm at 4:18 1.7cm at 4:50.

Keeping track of the emery and water was somewhat difficult, but we used approximately 7 cups of emery and 7 cups of water. The people doing the sawing could feel when we needed more emery and water, which was fairly often, as it would get pushed out of the cut through the sawing process. Overall, it was not horribly physically strenuous, but rope burn and cramps were the main bottlenecks to people being able to keep going.

The next day, we measured the depth of the cut at various points along the cut, represented in the table below and by the graph.

Length(cm)	Depth cut(mm)
0	1.49
1	2.4
2	3.46
3	4.8
4	6.24
5	7.36
6	8.94
7	9.65
8	10.56
9	11.37
10	12.11
11	12.81
12	13.53
13	13.87
14	14.27
15	14.58
16	14.69
17	14.68
18	14.35
19	14.24
20	14.2
21	13.99
22	14.18
23	13.92
24	13.77
25	13.65
26	13.41
27	13.06
28	12.7
29	12.25
30	11.77
31	10.58
32	10.2
33	9.19
34	8.17
35	6.83
36	5.5
37	4.51
38	3.22
39	2.3

Using this information, one can take 2 points on this graph to recover the radius of the pendulum; this will only be approximate as the radius relative to the ground changes throughout. Using this, I got that the pendulum should’ve been around 1.575 meters.