Recap of 2/28/08 Class

I don't know if I got the right order on these.

-Prof. makes coffee

-Prof. Mason talks about Raman who won a Nobel Prize for his work on scattering light

-Students counted off into groups by sequence of prime numbers

-Groups are asked to predict which string would break in a setup of weights and string. The answer was It depends on how string is pulled. The reason is because of the laws of inertia

-Prof. Mason talked about uncertainties in answers.

Themes of the Course

In science and engineering, we make decisions based on measurements. To make these decisions, we must evaluate

•What the data tells us –are there any trends?

•How good is the data –is it consistent, repeatable, accurate?

•How certain are we of any conclusions we make?

•Does the data agree with a theoretical model?

•How do we present the results?

During the course we will cover the topics of:

•Statistics

•Probability

•Error Propagation

•Regression/Curve Fitting

•Graphing practice

Definitions

The result of an experiment is given in the form:

Best Estimate of a quantity +- Uncertainty Units

This course deals with finding 1 and 2 from your data. It is assumed that many individual measurements of quantities are available so that we can apply “statistical analysis”.

TRUE VALUE = ACTUAL VALUE of the quantity (unknown in general)

ERROR= Difference between TRUE VALUE and Best Estimate (unknown)

UNCERTAINTY= Estimate of the ERROR.

The process of obtaining the best estimate for the Error is referred to as “Error Analysis”.

Further Definitions

Types of error/uncertainty:

•Mistakes: (eg. Wiring a circuit incorrectly, reading the wrong number on a digital display, bumping a balance, etc.)

Avoid them by being careful!

•Systematic error: The way in which the measurement is made leads to a consistent skew in the values recorded. Examples:

•a voltmeter that consistently reads 1% too high;

•impurities present in the water used change its density, viscosity, conductivity, solubility, etc.

•reading a graduated cylinder downward at an angle and thus getting a smaller value than actual

Avoiding and accounting for systematic errors is the heart of experiment design and planning.

It is very important to design your calibrations in great detail and to ensure that you have as accurate a knowledge of uncertainties arising from systematic errors.

Random errors and uncertainties: Random data fluctuations

Examples include:

•a digital display can only be read with certainty to the last decimal place –the “true value” is actually somewhere in between.

•noise (whether due to fundamental reasons, power lines digital instruments, nuclear decay, etc.) causing random fluctuations in a measured signal

•the inherent roughness of surfaces means that at some point the “length” of an object varies

•the random occurrence of nuclear decay

By repeating measurements and applying statistical techniques, these uncertainties can be estimated and possibly reduced

-Groups asked to estimate how much everyone in the world weighs together and how many heartbeats in your lifetime. Answers were given with uncertainties.

-Groups had a review question on vectors.

-Class checked out laptops and did a tutorial on vpython. A ball was created to start out and the final product was a ball bouncing around in a box.

-Students were introduced to class lab assistant

-Prof. mason told class how he wants the lab reports and pre-labs.

-Homework was given:
Finish vpython project
HINT: ball.velocity = ball.velocity + ball.acceleration * dt

Mastering Physics
Lab Report
Pre-lab (can we get notes on these posted on the blog)

-Assigned me to do the blog (GREAT JOB ROBERT!)

-Groups were created for the first huge project "Out 'N Back"

Writeup of First Lab (Measurement)

Write up of First Lab:

1) Write-up in your lab notebook on measurement of acceleration due to gravity from motion detector.

• What did you measure
• How did you measure it
• What were your results?

2) Write-up in your lab notebook on measurement of acceleration due to gravity from Video Analysis.

• What did you measure
• How did you measure it
• What were your results?

3) Write-up in your lab notebook on measurement variability.

• Find the % difference between the results of the two experiments.
• Discuss sources of error for each experiment
• Estimate the uncertainty for each of the measurements
• Do the measurements agree within your estimated uncertainty?
• Which of the measurements is more useful and why?

Emphasis should be on Analysis NOT Procedure! (Procedure should be quick one or two sentences that describe the general outlines of the experiment)

Introduction to Logger Pro and Video Analysis

Professor Mason spent the first 10 minutes of class introducing himself and describing his background.

• He started in Electrical Engineering
• He worked in design and instrumentation for X ray detectors.
• He did his graduate work in Physics
• He worked for a company that made bearings

The class was given a problem with two views of a three dimensional structure and asked if the lines in the structure interested.

The class was asked to define Science.

• Science is based on experiment
• Science is the study of nature
• Good experimentation has certain requirements

The class was asked to decide if a large graduated cylinder would fit into a round bottom flask. Sphere have the largest volume for a given surface area.

The class was asked how to prove something to be true. Professor Mason picked on every answer until it was apparent that proving truth was not possible according to his definitions.

The class was asked to judge how a mass on a spring attached to a cup would move if the cup was dropped. People drew free body diagrams to analyze the system.

The class was asked to define reality. There was general agreement that reality is personal and thus different for each individual.

Students were asked about to analyze how a meterstick would fall if its points of support were moved.

After a break we did a lab on using the Logger Pro and Video analysis.

Learning to use and setup LabPRO.

1. My group and I were given the task to measure acceleration due to gravity on a motion detector, and acceleration due to gravity from vidoe analysis.


2. We began by setting up the motion detector and opening up Logger Pro to record our graphs and data. Once we had a correct setup by adjusting some some rates, we began experiminting.


3. We began an eperiment with a ball, meausuring acceleration due to gravity of the falling ball. I held the ball just below the motion detector and one of my group members hit the collect button to collect data and i released the ball about a second the motion detector started clicking.

• We observed our graph displayed


• We then highlited the part where the ball was going down (stright line) , ignoring the bounce


• We fit a line to the graph, which gave us the slope and itercept

4. The results of our graph gave us the equation y=mt+b, were the slope of the graph was the acceleration, and the b was the y intercept (being 0). So we saw the connection of the equation V=at+vi. In our results our acceleration calculated to be 10.53 on the inital slope, but we also looked at the line after the bounce to have 9.87, we took an average of the two and got a calculation of 10.2, wich was reasonalbly close to the actual value of acceleration.

Video analysis

1. After completing the motion detector experiment, we used little cameras to record a bouncy ball falling towards the floor. We set up our lab by connection the camera and adjusting the settings to take a 5 second movie, adjusting the gain to the max(about 255 i believe), adjusting the shutter to 1, and changing the exposure to manuel with a value of 150. Now we were ready to experiment by making a movie.

• My group member was set to shoot the video, the other was holding a meter stick, and i was holding the ball to be released.
• We began to shoot the movie having some problems with pixels, and after some help from our professor we realized there was a chat program running taking away about 100 pixels.
• We finally shot a movie with 148 pixels and played it in slow motion allowing us to see the ball falling with no smudges.

2. We then opened the video analysis tools, and had a graphed displayed. The graph displayed position vs. time, and from here we set up to see the y-axis of the graph. We set a scale of 1m, wich was the size of the meter stick, and added pts. to were the ball began to fall from my hand till it almost hit the floor, and after we did that we played the video were it also gave us the position(y axis) vs. time and saw a parabola graph.

• We fitted a curve fit line to the graph
• We aquired our data having -5.2 being the acceleration to be -10.4

3. Then after the experiment professor Mason gathered different data of acceleration comparing them and taking an average. We also observed how there was a margin of error in calculations wich needed to be adressed, and so he adressed it to be + or - .056

Welcome to Physics 4A

Welcome to Physics 4A.

There are several assignments today:
1. Login to Mastering Physics, create an account and do the first assignment
2. Buy the lab manual at Day and Nite books
3. Buy a Carbon Copy Lab Notebook (Day and Nite or Bookstore)

Things to bring to class.
1. Lab Manual
2. A USB stick
3. Lab Notebook
4. A laptop if you have one.

We will be looking at computational modeling in class and introducing the first project.

My main webpage is at www.profmason.com
Class notes are located at:
http://physics.mtsac.edu/4A/4ANotes.htm