Your 'torques' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Your optional message or comment: **
Dave,
Two questions:
On 10-19 I sent you an email with the FORCE vs DISPLACEMENT experiment attached as a WORD document because I had a computer problem and was forced to save it as a WORD document on short notice and then finish it. Did you receive it? It has not shown up with comments on my access page. Please let me know if you want me to resend.
Screen shots don't convert to text, so I have no way of posting the work you sent me. However I should have posted my comments; apparently I didn't, which means that my comments went astray at some point. I'll track them down and try to post them tomorrow.
Basically there wasn't much to say except that you did just about everything correctly. There were a couple of minor notes, but I don't remember the specifics.
question #2:
What material will be on test #1? I'm confused since there are so many different sources for assignments and they are not in phase with each other.
The various sources of information and the assignemnts coming from each such as text assignments, experiments, intro problem sets, random problem sets, q a's, query's, class notes,synopsis,are significantly out of phase with each other. Some subjects (like vectors) have been covered in some sources and not yet in others. Same with rotational motion.Same with projectile motion. Same with linear momentum. I will definitely take a practice test.
The practice tests will help clarify the material and the emphasis, but the test basically covers everything assigned through work-energy. It is possible that some questions related to impulse-momentum will also appear; if so they are at the level of the Introductory Problem Set so basic knowledge of that set is all that's required. In a nutshell, all text assignments through Chapter 6, plus Introductory Problem Set 4.
Nearly half the test is a repeat of selected problems from the Major Quiz test bank.
** Positions of the three points of application, lengths of systems B, A and C (left to right), the forces in Newtons exerted by those systems, description of the reference point: **
3cm,9cm,13cm
7.6cm,8.0cm,7.9cm
1.1N,3N,1.9N
left end of rod
force vs length best fit graphs
this is setup for intial experiment
** Net force and net force as a percent of the sum of the magnitudes of all forces: **
0
0%
Fnet calculated by adding total of upward and downward forces
** Moment arms for rubber band systems B and C **
8cm,4cm
distance from fulcrum (point A) of points B and C
** Lengths in cm of force vectors in 4 cm to 1 N scale drawing, distances from the fulcrum to points B and C. **
4.4cm,12cm,7.6cm
8 cm,4 cm
The length of the force vectors for B,A,C then moment arms for B and C
** Torque produced by B, torque produced by C: **
+8.8N*cm, -7.6 N*cm
torques applied at points B and C
** Net torque, net torque as percent of the sum of the magnitudes of the torques: **
+1.2 N*cm, 7%
torque at B minus torque at C and net torque as a % of total torque. This is the error in my experiment because net torque should be zero.
** Forces, distances from equilibrium and torques exerted by A, B, C, D: **
1.3N,0,0,1.5N,1,+1.5N*cm,.8N,15cm,-12N*cm,1.0N,17cm,+17cm
Force,distance from point A,and torque for A, B, C
** The sum of the vertical forces on the rod, and your discussion of the extent to which your picture fails to accurately describe the forces: **
0
Net vertical forces are zero, but they are not uniformly applied at all locations so there is torque on the rod
** Net torque for given picture; your discussion of whether this figure could be accurate for a stationary rod: **
+6 N*cm
Not sure. Is it correct or relevant to choose A as the fulcrum?
Any point can be chosen as the fulcrum; it's often good to choose a point at which one of the forces is applied, since that force would not produce a torque about its point of application, which simplifies the equations.
The net torque of a stationary rod, about any point, is zero.
Given the magnitudes of the torques involved, 6 cm * N could be within experimental uncertainty of 0, though it's a little bit of a stretch.
** For first setup: Sum of torques for your setup; magnitude of resultant and sum of magnitudes of forces; magnitude of resultant as percent of sum of magnitudes of forces; magnitude of resultant torque, sum of magnitudes of torques, magnitude of resultant torque as percent of the sum of the magnitudes: **
+8.5N*cm
0,4.6N
0
+8.5N*cm,30.5N*cm,27%
** For second setup: Sum of torques for your setup; magnitude of resultant and sum of magnitudes of forces; magnitude of resultant as percent of sum of magnitudes of forces; magnitude of resultant torque, sum of magnitudes of torques, magnitude of resultant torque as percent of the sum of the magnitudes: **
+1.0N*cm
.5N,6.8N
7%
-10.0N*cm,46 N*cm
** In the second setup, were the forces all parallel to one another? **
Since the rod's right end got pulled down the forces o the left end canged direction very little but the ones on the right changed by about 10 degrees
** Estimated angles of the four forces; short discussion of accuracy of estimates. **
Band C makes about a 100deg angles with the rod and band D chnaged to about 80 degrees. A and B changed very little.
** x and y coordinates of both ends of each rubber band, in cm **
+2,0,+2,+8
+8,+10,+8,+17.7
+17.5,+.8,+13.5+8
coordinates for bottom then top of bands B,A,C
** Lengths and forces exerted systems B, A and C:. **
8.0, 1.5N
7.7, 3.0N
8.2, 1.9N
** Sines and cosines of systems B, A and C: **
vertical
vertical
-.866, .5
** Magnitude, angle with horizontal and angle in the plane for each force: **
1.5N,90deg
3N,90deg
1.9N,30deg
** x and y components of sketch, x and y components of force from sketch components, x and y components from magnitude, sine and cosine (lines in order B, A, C): **
vertical x=0 y=+3N
vertical x=0 y=-1.5N
x=+.95N y=-1.6N
** Sum of x components, ideal sum, how close are you to the ideal; then the same for y components. **
+.95N,0,.95N
-.1N,0,.1N
Was off more in the X direction but the clip graps the threaded rod sort of funny and may distort angles some.
** Distance of the point of action from that of the leftmost force, component perpendicular to the rod, and torque for each force: **
0,-1.5N,0
6,+3.0N,+18N*cm
11.5,-1.6N,-18.4N*cm
** Sum of torques, ideal sum, how close are you to the ideal. **
-.4 N*cm,0,.4N*cm
was off by .4 N*cm
** How long did it take you to complete this experiment? **
5 1/2 hours! very time consuming - way too long.
** Optional additional comments and/or questions: **
I thought I'd try something different by printing the entire experiment and reading through the entire thing before starting. I felt I was spending too much time and getting confused because if you do them on the screen you're forced to constantly go back and look for data and instructions in previous parts of the assignment and then finding your place again and so forth. It helped (a little). This experiment took 24 pages to print out!
Am I doing something wrong to be spending this much time???????? Any helpful suggestions or comments?
Your work is excellent.
With respect to the time you report, it is again in the upper part of the commonly reported range of times.
How much of your time do you estimate was spent on reading and understanding instructions, how much on setup, and how much on analysis?