course Phy 201
When doing the open queries, is using this submit work form the acceptable method for getting the work to you?
ph1 query 0Most queries in this course will ask you questions about class notes, readings, text problems and experiments. Since the first two assignments have been lab-related, the first two queries are related to the those exercises. While the remaining queries in this course are in question-answer format, the first two will be in the form of open-ended questions. Interpret these questions and answer them as best you can.
Different first-semester courses address the issues of experimental precision, experimental error, reporting of results and analysis in different ways and at different levels. One purpose of these initial lab exercises is to familiarize your instructor with your work and you with the instructor 's expectations.
Comment on your experience with the three lab exercises you encountered in this assignment or in recent assignments.
Question: This question, related to the use of the TIMER program in an experimental situation, is posed in terms of a familiar first-semester system.
Suppose you use a computer timer to time a steel ball 1 inch in diameter rolling down a straight wooden incline about 50 cm long. If the computer timer indicates that on five trials the times of an object down an incline are 2.42sec, 2.56 sec, 2.38 sec, 2.47 sec and 2.31 sec, then to what extent do you think the discrepancies could be explained by each of the following:
The lack of precision of the TIMER program.
To what extent to you think the discrepancies are explained by this factor?
Your answer: The lack of precision of the timer program is that it is only accurate to a certain degree.. In this case it seems as those the timer program is only accurate up to about .1 second, therefore it only gives a general estimate of what the true precise time would actually be.
The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
To what extent to you think the discrepancies are explained by this factor?
Your answer: The decrepencies in time are more likely due to this factor than the actual timer being wildly inaccurate or unprecise. The reaction time of the person clicking on the mouse has a very great likelihood of fluctuating. Even when getting in a steady rhythm it is still quite easy for a person to miss a click or lose their rhythm.
Actual differences in the time required for the object to travel the same distance.
To what extent to you think the discrepancies are explained by this factor?
Your answer: A discrepancy such as this could only happen if certain factors were changed from trial to trial. I find it unlikely that an object traveling the same distance under the same conditions would have a discrepancy in the time that it took to travel this distance.
Differences in positioning the object prior to release.
To what extent to you think the discrepancies are explained by this factor?
Your answer: I believe that the factor of positioning plays the largest factor in changes or discrepancies in time. When changing the position of of the object prior to release, this alters many other factors as well such as velocity, speed, and distance. By changing up all these factors there is bound to be a discrepancy in the times that it takes the object to travel.
Human uncertainty in observing exactly when the object reached the end of the incline.
To what extent to you think the discrepancies are explained by this factor?
Your answer: In many instances the objects travel so fast that it is difficult for the human eye to tell exactly when the object reached the end of the incline. This also does play a big role in the discrepancies. From each trial to the next it is highlyunlikely that a human will observe the object reaching the end of the inclince at the exact same time. Reaction time and how well a person is focused on and paying attention to the positioning of the object are factors in the determination of when the object would reach the end of the incline. Therefore, precision would almost indefinitely be off in this case.
Question: How much uncertainty do you think each of the following would actually contribute to the uncertainty in timing a number of trials for the ball-down-an-incline lab?
The lack of precision of the TIMER program.
To what extent to you think this factor would contribute to the uncertainty?
Your answer: As was stated previously, the timere is only accurate to a certain extent. It would give you a decent estimate of the times, but no tool is perfectly accurate so there would still be a marginal amount of uncertainty due to this factor.
The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
To what extent to you think this factor would contribute to the uncertainty?
Your answer: This factor would play a very large role in uncertainty. There is a great chance in fluctuation of a humans reaction when clicking the mouse. There is no systematic or mechanical way to go about clicking the mouse to ensure that you are getting the same click each time so the uncertainty due to this factor is large.
Actual differences in the time required for the object to travel the same distance.
To what extent to you think this factor would contribute to the uncertainty?
Your answer: I find that this factor would have the least affect on time differences. An object under the same conditions and traveling the same distance, should basically have no differences in timem therefore the uncertainty of this factor seems to be quite low.
Differences in positioning the object prior to release.
To what extent to you think this factor would contribute to the uncertainty?
Your answer: There would be quite a bit of uncertainty due to the changing of position of the object prior to release. In this case there would nearly always be a difference in time it took the object to travel. This would account for differences in time and the uncertainty with this would most likely result from not timing each position multiple times. Also when completely multiple trials you would have to be precise in your positioning, making sure to place them in the exact same place each time you repeat a trial of the same position. This would also take into account human error/ uncertainty again.
Human uncertainty in observing exactly when the object reached the end of the incline.
To what extent to you think this factor would contribute to the uncertainty?
Your answer: Human error in observation and reaction seem to be the biggest factor in discrepancy and uncertainty in any case. It is unlikely that a human would precisely and accurately observe the object reaching the end of the incline at the same exact time during multiple trials.
Question: What, if anything, could you do about the uncertainty due to each of the following? Address each specifically.
The lack of precision of the TIMER program.
What do you think you could do about the uncertainty due to this factor?
Your answer: There is not much that could be done to change the uncertainty of this factor. No tool or program is indefinitely accurate so there will always be, to some degree or other, a lack of total accuracy and precision.
The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
What do you think you could do about the uncertainty due to this factor?
Your answer: To cut down on uncertainty in this case, it would be wise to practice clicking many many times to get yourself in a rhythm before actually doing an experiment.
Actual differences in the time required for the object to travel the same distance.
What do you think you could do about the uncertainty due to this factor?
Your answer: The only thing that could be done about uncertainty in this case, would be to make sure that the conditions in which the object are traveling in and the distance that it is traveling are the same for each trial. Otherwise, there shouldnt be any uncertainty due to this factor.
Differences in positioning the object prior to release.
What do you think you could do about the uncertainty due to this factor?
Your answer: Making sure that each time you change the positioning of the object, you document it and do a trial for each position multiple times would help to cut down on uncertainty.
Human uncertainty in observing exactly when the object reached the end of the incline.
What do you think you could do about the uncertainty due to this factor?
Your answer: To cut down on uncertainty is human oberservation, it would be best to complete this experiement in a place where there are no other distractions, ensuring that all your attention and focus is on the task at hand.
Question: If, as in the object-down-an-incline experiment, you know the distance an object rolls down an incline and the time required, explain how you will use this information to find the object 's average speed on the incline.
Answer: In this case, if you know the time as well as the distance, and for instance say the time is 10 seconds, and the distance is 20 cm, you divide the distance by the time which would give you an average speed of 2 cm per second.
Self-critique (if necessary):
Question: If an object travels 40 centimeters down an incline in 5 seconds then what is its average velocity on the incline? Explain how your answer is connected to your experience.
Your answer: displacement = 40 cm (40 cm 0 cm = 40 cm) elapsed time= 5 seconds. Velocity = 40/5 = 8 cm / second
Self-critique (if necessary): I know that the average velocity is the displacement divided by the elapsed time, but Im not quite sure in this case if I have the displacement correct. I feel that I have only found the average speed and not the average velocity. Is this correct?
Question: If the same object requires 3 second to reach the halfway point, what is its average velocity on the first half of the incline and what is its average velocity on the second half?
Answer: 1st half: displacement = 20 cm (20 cm 0 cm = 20 cm) elapsed time= 3 seconds average Velocity = 20 cm / 3 s = 6.7 cm / s
2nd half: displacement= 20 cm (40 cm 20 cm = 20 cm) elapsed time= 2 seconds average Velocity = 20 cm / 2 s = 10 cm / s
Self-critique (if necessary): As long as I am following the formula for average velocity right, I believe I understand how to do this sort of problem appropriately.
Question: `qAccording to the results of your introductory pendulum experiment, do you think doubling the length of the pendulum will result in half the frequency (frequency can be thought of as the number of cycles per minute), more than half or less than half?
Answer: Based on my findings, it seems as though even if you double the length of your pendulum the frequency will be a little less than half.
Self-critique (if necessary):
Question: `qNote that for a graph of y vs. x, a point on the x axis has y coordinate zero and a point on the y axis has x coordinate zero. In your own words explain why this is so.
Answer: When a point falls either on the x, or the y, axis it cannot be in any other position than zero on the alternate axis. Otherwise, the point would not lie exactly on either axis.
Self-critique (if necessary):
Question: `qOn a graph of frequency vs. pendulum length (where frequency is on the vertical axis and length on the horizontal), what would it mean for the graph to intersect the vertical axis (i.e., what would it mean, in terms of the pendulum and its behavior, if the line or curve representing frequency vs. length goes through the vertical axis)? What would this tell you about the length and frequency of the pendulum?
Answer: This would mean at some point the length would have to be zero.
Self-critique (if necessary): I trying to relate this to the previous question and this is the only logical answer I can come up with. If the line or curve went through the y-axis at some point, would that not mean that at that time the x coordinate at that point was zero, thus in this case making the length zero?
Question: `qOn a graph of frequency vs. pendulum length, what would it mean for the graph to intersect the horizontal axis (i.e., what would it mean, in terms of the pendulum and its behavior, if the line or curve representing frequency vs. length goes through the horizontal axis)? What would this tell you about the length and frequency of the pendulum?
Answer: This would mean that at some point the frequency of the pendulum was zero.
Self-critique (if necessary): This relates to the past 2 questions. If the line or curve passed through the x-axis at some point, then the coordinate of the point on the y-axis would have to be zero. Would this not account for the frequency of the pendulum to be zero in this case?
The graph could go through the y axis, but this would correspond to a pendulum that takes infinitely long to complete a cycle, and wouldn't represent any real pendulum.
Question: `qIf a ball rolls down between two points with an average velocity of 6 cm / sec, and if it takes 5 sec between the points, then how far apart are the points?
Your solution: 6 * 5 = 30, This means that the 2 points were 30 cm apart. If the ball rolled 6 cm in 1 sec then you multiply 6 times the 5 seconds which would give you 30 cm in 5 seconds.
Given Solution:
`aOn the average the ball moves 6 centimeters every second, so in 5 seconds it will move 30 cm.
The formal calculation goes like this:
We know that vAve = `ds / `dt, where vAve is ave velocity, `ds is displacement and `dt is the time interval.
It follows by algebraic rearrangement that `ds = vAve * `dt.
We are told that vAve = 6 cm / sec and `dt = 5 sec. It therefore follows that
`ds = 6 cm / sec * 5 sec = 30 (cm / sec) * sec = 30 cm.
The details of the algebraic rearrangement are as follows:
vAve = `ds / `dt. We multiply both sides of the equation by `dt:
vAve * `dt = `ds / `dt * `dt. We simplify to obtain
vAve * `dt = `ds, which we then write as{}`ds = vAve *`dt
Be sure to address anything you do not fully understand in your self-critique.
Self-critique (if necessary):
Question: `qYou were asked to read the text and some of the problems at the end of the section. Tell your instructor about something in the text you understood up to a point but didn't understand fully. Explain what you did understand, and ask the best question you can about what you didn't understand.
Self-critique (if necessary): I understand the usefullness of te Order of Magnitudes, and how that you round off all numbers to a significant figure and its power of ten, but once I got into reading the useful examples of how to use this rule Im not understanding the equations they are using. For instance, in example 1-8 (total number of heart beats) I do not understand how they are coming up with the equation (80 beats/ min) (1 min / 60 s) (2 * 10^9s) = 3 * 10^9 . In this equation the part that I do not understand is where is the (2*10 ^ 9 s) is coming from. I referred to table 1-2 that they pointed out, but on my own I would not know how to incorporate this into the rest of the equation. How do I go about being able to know what to do in this case?
2 * 10^9 seconds is a reasonable estimate of a human lifetime (70 years or so).
Question: `qTell your instructor about something in the problems you understand up to a point but don't fully understand. Explain what you did understand, and ask the best question you can about what you didn't understand
Number 10 in the problems, which is asking for the area and approx. uncertainty of a circle of radius 3.8 * 10^4 cm. I understand how to find the area, but when finding the uncertainty, do I just take the solution of the area and then plug that number into the equation for percent uncertainty? And does this apply the rule that I use only the number of significant figures in the in the problem or should I round that to the nearest ten or tenth?
This problem will be addressed in more detail in an upcoming query.
A short synopsis:
3.8 is the 2-place rounding of any number between 3.75 and 3.85. Find the areas of circles of radii 3.75 * 10^4 cm and 3.85 * 10^4 cm, then find the difference between either of these results and the result you get for 3.8 * 10^4 cm. That's an estimate of your uncertainty.
Alternatively find the .05 cm uncertainty in radius as a percent of the radius. The area involves the square of the radius, so will have double the percent uncertainty of the radius.
&#This looks good. See my notes. Let me know if you have any questions. &#