060915

Quiz

1.  Write down the equations of uniformly accelerated motion.

 

 

2.  Circle the quantities which could possibly be a value of `ds:

5 cm                 20 sec              3 cm/s^2          15 cm/s            12

Circle the quantities which could possibly be a value of vAve:

5 cm                 20 sec              3 cm/s^2          15 cm/s            12

Circle the quantities which could possibly be a value of `dt:

5 cm                 20 sec              3 cm/s^2          15 cm/s            12

3.  Identify v0, vf, a, `dt, `ds for each of the following and indicate which equations or equations of uniformly accelerated motion could be used to find additional information.  Also sketch a v vs. t graph for each and label the axes with all possible given information:

a.  If an object dropped from rest falls 130 cm in .52 seconds, what is its acceleration?

 

b.  If an object accelerates at 1000 cm / s^2, then how long does it take to travel 20 cm starting from rest?

 

c.  An object travels 50 cm while accelerating uniformly at 20 cm/s^2.  It started out moving at 30 cm/sec.  Of the variables v0, vf, `ds, a and `dt, which do you know and what is the value of each?  Which equations of uniformly accelerated motion can be used to obtain the values of additional variables?

4.  This question is diagnostic and won’t be counted against you, though if you get it you will get credit for doing so):  Solve the equation vf^2 = v0^2 + 2 a `ds for a, showing the steps of your algebra.

 

5.  Solve the problems in #3 above.

Downloading the TIMER program:

Log in to Blackboard at bb.vccs.edu using username vhstudent and password vhstudent.

Click on the 'course' Supervised Study Supervised Study.

Click on Course Documents.

The second item down is entitled q_a_prelim.  Under that heading is a program entitled 'create vhmthphy'.  Run that program; this only takes a couple of seconds.

Scroll down the Blackboard page to Course Documents.

Scroll down that page to Physics I.

Scroll down until you find the heading 'TIMER program'.

Save the program to the desktop or any other convenient location.

Go to http://www.vhcc.edu/dsmith/forms/ph1_timer_experiment.htm.  If you didn't obtain your data in class, you should simply fill in the form according to instructions on the form, and submit it.  If you did obtain your data in class, you will need to follow the instructions on the form it was handed out in class.  You also have the option of simply completing the form online, which you might find quicker and more convenient.

Follow the instructions down to the point where you are instructed to 'copy your data into the box below'.  Be very sure you include your name and your VCCS email address.  If you don't know your VCCS email address see the instructor.

Submit the form.

Open your student email, or any other Internet email account you might have, and email yourself a copy of your data.

Next, use the TIMER to do the following:

1.  Time the ball down the 2-ramp system, as before.  Time from A to B, from A to C and from A to D.  For homework you will repeat your analysis of the horizontal motion of the ball for each phase, and of the vertical motion of the last phase.

2.  Time the bracket pendulum, using the same pendulum length you used to measure the motion of your system, from release to the second 'hit', from release to the fourth 'hit', from release to the sixth 'hit', from release to the eighth 'hit', from release to the tenth 'hit', etc., until the very last 'hit'.  For homework you will then do the following:

The instructions for the entire form are copied below.  You need to complete the instructions as part of your homework for the weekend.  If the instructor hasn't handed out a copy of these instructions, remind him to do so.

Using the TIMER program

Select the following option (you have only one choice):

Your course (e.g., Mth 151, Mth 173, Phy 121, Phy 232, etc. ):

If you have one, please provide your access code.  You may leave this part blank if you do not yet have an access code. 

If you do not have an access code and have not already done so, you need to immediately go to http://vhmthphy.vhcc.edu/ > General Information, click on Request Access Code and submit the completed form. 

Remember that it is crucial to enter your access code correctly.  As instructed, you need to copy the access code from another document rather than typing it.

Access Code:
Confirm Access Code:

Your Name:

First Name
Last Name

Your VCCS email address.  This is the address you were instructed in Step 1 to obtain.  If you were not able to obtain that address, indicate this below.

Please insert any message you wish to share with the instructor at this point:

 


 

The Timer Program should have been downloaded from Supervised Study Current Semester > Downloads > Physics I.  It opens in a small window and can be run side-by-side with other windows on your computer (just size the second window so it leaves room for the Timer program).

It is easy to operate the Timer program.  All you have to do is click on the button labeled Click to Time Event.

Click that button about 10 times and describe what you see.

Now click on Initialize Counter, which will clear all the data from the timer window.  Click the mouse as fast as you can until the TIMER window fills up.  Be sure you get at least 20 time intervals.

Copy your data into the box below.

You got at least 20 time intervals.  Based on your data what was the average of the first 20 time intervals?  Note that you could get this average by averaging the first 20 intervals.  My first few intervals were .15625, .15625, .1875, .171875, etc; I could just add up the first 20 intervals and divide by 20 to get the average.  However there is an easier and quicker way to get the result, so use the easier way if you can.

Give your result, number only, in the first line, and starting in the second line explain how you got it.

When I did this activitiy the first few lines of my data were as follows:

event number clock time time interval
1 11.67188 11.67188
2 11.875 0.203125
3 12.0625 0.1875
4 12.20313 0.140625
5 12.375 0.171875
6 12.54688 0.171875
7 12.73438 0.1875
8 12.92188 0.1875
9 13.10938 0.1875
10 13.28125 0.171875
11 13.4375 0.15625

It looks like the same intervals keep popping up.  For example .1875 seconds occurs 5 times out of the first 10 intervals, .171875 seconds occurs three times, and .203125 seconds, .140625 seconds and .15625 seconds each occur once.

A frequency distribution for my time intervals would be as follows:

time interval frequency
,140625 1
.15625 1
.171875 3
.1875 5
.203125 1

What different time intervals did you observe in your first 20 intervals, and how many times did each occur?  List in the box below the different time intervals you observed and the number of times each occurred.  List from the shortest to the longest interval, and use a comma between the time interval and its frequency.  For example if my data above would be listed at

.140625, 1

.1565, 1

.171875, 3

.1875, 5

.203125, 1

Your list should be in exactly this format, with no other symbols or characters.

You may make any comments or ask any question about the process so far in the box below

On the 10 intervals I've shown you, do you really think I managed to get a time of .1875 seconds, accurate to 4 significant figures, on half of the intervals?  If you do, I'm grateful for your confidence but I'm just not that good.  No human being has that much neurological and muscular control.

So why do you think the TIMER program reported that time so frequently?  Why weren't there times like .1830 seconds, or .1769 seconds?  Does this mean that the TIMER program is flawed?  Does that mean it's useless?

Here are a few more lines of data, with an added column showing the difference between each time interval and the next.

clock time time interval difference from one time interval to next
9 13.10938 0.1875 -0.01563
10 13.28125 0.171875 -0.01563
11 13.4375 0.15625 0.03125
12 13.625 0.1875 -0.01563
13 13.79688 0.171875 0.015625
14 13.98438 0.1875 0.015625
15 14.1875 0.203125 -0.03125
16 14.35938 0.171875 -0.01563
17 14.51563 0.15625 0.03125

Take a good look at that last column and tell us what you see in those numbers, and what this tells you about the TIMER program

Now initialize the TIMER once more, and take a series of 10 relaxed breaths.  Every time you start to inhale, hit the TIMER button.

My results for the first 7 complete breaths are as follows:

series of relaxed breaths  
event number clock time time interval difference between time interval and next
1 1569.734 1569.734  
2 1582.75 13.01563 0.32812
3 1596.094 13.34375 3.90625
4 1613.344 17.25 2.70313
5 1633.297 19.95313 1.35937
6 1654.609 21.3125 4.23438
7 1680.156 25.54688 2.15625
8 1707.859 27.70313  

I didn't go on because the time between my breaths kept increasing, and I was afraid if I relaxed any more I might stop breathing altogether.  It's going to take either more statistical analysis to determine whether that's a real danger, or a little common sense.

Report your results by just entering your time intervals, one to each line, in the box below.  If I was entering my results I would enter

13.01563

13.34375

17.25

19.95313

21.3125

etc.

Enter your results in the same format:

If you have any comments please insert them here

Most likely you did not observe the same exact time interval twice, and if you did it did not happen nearly as often as when you did the fact clicks.

Why do you think this exactly what we would expect?

Which of the following statements do you think is the most accurate?

a.  The TIMER program is capable of determining the time between two events accurately to within about .1 second.

b.  The TIMER program is capable of determining the time between two events accurately to within about .01 second.

c.  The TIMER program is capable of determining the time between two events accurately to within about .001 second.

d.  The TIMER program is capable of determining the time between two events accurately to within about .0001 second.

Enter your answer and your reasoning in the box below:

Note that the TIMER can save your data in a format that can be read by a spreadsheet.  This will be very handy in the future, so take a minute and do the following:

1.  Click on the button at the lower right of the TIMER form, entitled Click to File Data.

2.  A box will pop up allowing you to include an identifying message. You should generally choose to include such a message; for the data presently on your timer that might be 'series of regular breaths time at beginning of inhalation' or something similar.  Type in whatever you think would serve as a good identifier for this data and OK that box.

3.  A typical Save As window will appear.  Decide where to save your data and what to call it, and proceed to save it.  The program will save the file as a comma-delimited text file.

4.  Open your spreadsheet program (typically Excel) and choose File > Open.  Browse to the folder in which you just saved your data.  Below the File Name line will be a File Type line; set this either to Text Files or All Files so your file will appear.  Open it.

5.  A series of windows will typically appear.  In the first window make sure the file type chosen is Delimited, the proceed to the next window. 

6.  In the second window you will see a series of checkboxes; check the one entitled Comma, in order to select the comma-delimited file, then just click on Finish.

Your data should appear in your spreadsheet, and can be manipulated as in any spreadsheet.

Copy a few lines of the data from your spreadsheet into the box below:

Your instructor is trying to gauge the typical time spent by students on these experiments.  Please answer the following question as accurately as you can, understanding that your answer will be used only for the stated purpose and has no bearing on your grades: 

 

 


You may add optional comments and/or questions in the box below.

Examples of TIMER output, which shows clock time in the second column and time interval in the third.  The mouse was clicked with a typical time interval of .13 - .18 seconds.

1 15.40625 15.40625
2 15.59375 .1875
3 15.71875 .125
4 15.85938 .140625
5 15.99609 .1367188
6 16.17188 .1757813
7 16.29688 .125
8 16.78125 .484375
9 16.94922 .1679688
10 17.10938 .1601563
11 17.24609 .1367188
12 17.40625 .1601563
13 17.59375 .1875
14 17.76563 .171875
15 17.92188 .15625
16 18.09375 .171875
17 18.24609 .1523438
18 18.42188 .1757813
19 18.57422 .1523438
20 18.73438 .1601563
21 18.87109 .1367188