Principles of Physics
Download the following files:
 Syllabus
All the documents are available at the website:
http://www2.swccd.edu/~hlee
Introduction
Wilfred Hok Kong LEE, Ph.D.
Office: 343A
Mail box: MSE Office 215
Contact Info:
Email: hlee@swccd.edu
Phone: ext. 5533
Mon
Tue
Wed
Thu
11:45-1:30
1:15-2:00
11:45-1:30
1:15-2:00
Textbook & Course Homepage
Optional: University Physics with Modern Physics with
MasteringPhysics (13th edition) by Young and Freedman
Course Homepage:
http://www2.swccd.edu/~hlee
Lab manuals will be posted on this site. Print out the
lab manuals BEFORE you come to class.
Your scores will be posted on Blackboard Online:
Go to the Southwestern College homepage
http://www.swccd.edu
Click on “Online Class Login” under “E-Tools”
Grades
Lab Report
Final Exam
100 – 85%
84 – 75%
74 – 60%
59 – 50%
49 – 0%
80%
20%
A
B
C
D
F
Policy on Collaboration
You can work in groups, but you must write your solution
independently.
Students who copy or allow people to copy your work will get
zero.
Attendance, tardiness, cell phones,
pagers, etc…
You may be dropped from this class
If you are coming in late…
Classes start on the clock
Don’t slam the door and your backpack!
Don’t disturb the others, be quiet
Sign up on the “Black List” if you are late more than 10 minutes.
Ten points deducted from your next homework.
Lab Report (every 1-2 weeks)
1.
2.
3.
4.
5.
6.
7.
8.
9.
Name, ID & Date
Title
Purpose
Procedure
Data
Equations
Mathematical calculations
Sources of Error
Conclusion
Name and Date
Write your name on the top right hand corner
Include the names of your group members if you worked in a
group
Write the date you performed the experiment
NOT the date you write the lab report nor the date it is due
Title
Include the title of the lab. You may choose an appropriate
title if you wish.
Purpose
A description of what the lab is about. In your own words. Do
not copy and paste please.
Procedure
•Step by step
•No need to say “push button [D]…”
•Instead say “use computer to measure velocity…”
•Don’t say “take data” unless you say what the “data” is, e.g.
velocity, voltage.
Tips: Include diagrams
Data
This section must contain all the data you obtained in this
experiment. You can present it in a table format. You can use
the tables provided in your handout. Always include units
and use scientific notation when convenient.
Equations and Calculations
This section must contain equations and calculations you used.
Please be clear and organized. Show your work. I don’t want to
see just the final answer.
If there are more than one trial, show work for just one of them.
Multiple Trials
•If there are multiple trials, the calculations for each trial are
almost exactly the same.
•No need to write the calculations for every trial.
•Do a sample calculation for one of the trials. Indicate which
trial you are calculating, seeing that the calculations of one
trial is correct, I will trust that you know how to do the rest.
Sources of Error
No experiments are perfect
Common errors:
Friction, reaction time …
Unacceptable sources of error:
“I may have did the calculations wrong”
“I was careless”
Conclusion
Provide a summary of the experiment. Compare your results with
the theoretical value, if applicable.
Conclusion always has something to do with the purpose section.
BE QUANTITATIVE!!!
Examples of Conclusions
Acceptable
“the measured value is within 4.7% of the accepted value”.
“Newton’s Second Law is verified to within 3%”.
quantitative
Unacceptable
“the measured value is pretty close to the accepted value”, or
“Newton’s Second Law is correct”
too vague
Questions
Put your answers to the questions on the lab manuals after the
conclusion section.
Staple EVERYTHING
You lose points if you don’t staple your work together!!
Some (very) simple error analysis
For those who are interested:
http://www.upscale.utoronto.ca/PVB/Harrison/ErrorAnalysis/
http://www.ligo.caltech.edu/~vsanni/ph3/
You can download notes about data analysis from
these sites.
Percentage difference
Often one wants to compare two numbers, e.g.
u=12.4 and v=13.1 by evaluating their percentage difference.
12.4 - 13.1
´ 100% = 5.6%
12.4
or
Both are correct.
Usually when we calculate
percentage difference, the
two numbers are very similar
in value, so it does not matter
12.4 - 13.1
´ 100% = 5.3% which one we put in the
denominator.
13.1
Some common mistakes
Correct:
Incorrect :
12.4 - 13.1
´ 100% = 5.6%
12.4
or
12.4 - 13.1
´ 100 = 5.6%
12.4
or
12.4 - 13.1
´ 100% = 5.3%
13.1
12.4 - 13.1
´ 100 = 5.3%
13.1
or
12.4 - 13.1
´ 100% = -5.6%
12.4
The “%” sign is NOT optional, nor is the absolute value sign.
Mean (average)
Repeated measurements:
x = 1.3,1.6,1.5,1.3
1.3 + 1.6 + 1.5 + 1.3
(The mean of x) = x = x =
= 1.425 » 1.43
4
Common mistake:
x = 3, 3, 4
Too many digits
3+ 3+ 4
(The mean of x) = x = x =
= 3.333333333333
3
Usually, the mean has only slightly better precision, so keep to
at most one higher significant figure. The mean above should
be either 3.3 or 3.
Standard deviation σ
x = 1,2, 3, 3, 4, 5
x=3
N
s=
2
(x
x
)
å i
i =1
N -1
(x1 - x )2 + (x2 - x )2 +
=
N -1
+ (x N - x )2
(1 - 3)2 + (2 - 3)2 + (3 - 3)2 + (3 - 3)2 + (4 - 3)2 + (5 - 3)2
=
= 1.4
6 -1
The smaller the standard deviation, the more better are your
data.
Example
Find the σ of the following measurement of length x:
11.3cm, 11.7cm, 12.0cm, 11.8cm
11.3cm + 11.7cm + 12.0cm + 11.8cm
x=
= 11.7cm
4
N
s=
2
(x
x
)
å i
i =1
N -1
(x1 - x )2 + (x2 - x )2 +
=
N -1
+ (x N - x )2
(11.3 - 11.7)2 + (11.7 - 11.7)2 + (12.0 - 11.7)2 + (11.8 - 11.7)2
=
= 0.3cm
4 -1
Standard deviation
68% of probability lying within a width of 2σ.
Tips
Although it is often not asked explicitly, it is usually a good
idea to compute the standard deviation to see how far your
data are apart from each other.
You will get a better grade!
Linear plot
y = mx + c
y
m : slope (has the same unit as )
x
c : y-intercept (has the same unit as y)
Example:
a = g sinθ
Plot a vs sinθ. The slope will give g.