3/25 Tues Class Recap

The classroom only have around 5 people around 5oclck, which is very abnormal then usual. Then the professor came in and can't wait to start the class at exactly 5:25. First we separated to groups by human parts. Ankle, Brain .... etc
The video question of the day is a swinging ball on the hang on a board with a pin stick in the middle of board. When release the ball from a certain height and it will swing to the same height to the other end too.
Later Professor start lecture on Work and Energy, and we did some interesting Tarzan question.
All the notes can be found here under the Work Notes and Energy Notes.
http://physics.mtsac.edu/4A/4ANotes.htm
After lecture, professor talks about his nerve disorder around the jaw. Surprisingly, the class dismiss early. Our homework is only the Mastering Physics and the test is schedule to be next Tuesday. As for the Out 'N Back project, it is due when professor think we are ready.

Lets wish Professor Mason's pain will get much better with the medication treatment!!

Missing Class on Thursday

There was no class on Thursday. The mastering physics deadline was pushed back until Tuesday. The exam and project due date deadlines will also be pushed back to tuesday and ??? respectively.

Some of you may recall that I was uncomfortable in class on Tuesday. I went to the doctor on Friday and was diagnosed with Trigeminal Neuralgia. I am on medication for it and will visit a neurologist on Wednesday. I obviously hope to make a full recovery and minimize the disruptions to our class.

...and people said this was easy psh....3/18/2008

We began the class with a lecture on superconductors. It was rather interesting when MMason
started to talk about computers. After that topic we started to do a bit more force problems that
required some knowledge of kinematics. I do not think MMason separated everyone into groups. I think it was pretty much where you sat down for the day. Highly odd on MMason side. Anyways, we did your typical white board equations. Keith answers why the car picture was odd in comparasion to the problem that MMason gave us. MMason introduced us to two different types of problems. One was force drag and circular motion. Again we had to do your typical white board problems and work together to get the correct answer.....sometimes. We ended the class with the prelab we had to make previous of what MMason has instructed us to write up. The lab was about determining how much friction there was between the track and cart. I THOUGHT HE SAID THERE WILL BE NO WRITE UP!!!

You do not need to write up the POST LAB for the friction lab. (I assume all of your are diligently writing up the post labs for all our labs(answering the analysis and conclusion questions)) Therefore, when I read your lab notebook, there will be only a pre-lab on friction, but no post lab.

Anyways we started to clean up and he assigned the blog to me because I never got invited.

I also shared some ideas for how the make your out and back car work. To reiterate: your car needs to out AS FAR AS POSSIBLE and then make it back as close to the initial position as possible. Your car must go at least one meter for you to PASS! Here is a link to a site that has some great ideas on how to make your project work:

Me and my big mouth. Homework was Mastering Physics 8 and a prelab write up. Make sure you study your forces for tomorrow. We have our awesome Thursday quiz.

Thursday, 03/13/2008 Physics 4AG 17:25-21:05+++

Hi mates and my dearest Professor Mason,

Unfortunately, I am the one chosen to be writing the blog this time. As English is my 2nd language, please correct me if you see any grammar mistake or error. Thank you!

1) A wonderful quiz at the beginning of the class, it was about 30 mins. (Including the analysis by Professor Mason) It makes me starting to imagine about a flea that weights 100g for the rest of the night.

2)Discussion 1: A cart with a ball shooter move horizontally with a constant velocity, then shoot out a metallic ball with a constant velocity of during the movement. Will the ball fall a) back into the cart? b) fall behind of the cart? c) fall in front of the cart? The result is a); the ball will fall back into the cart. It is because the cart and the ball have the same horizontal velocity, so the distances they move are the same.

3) Discussion 2: Same situation as Discussion 1, but we used a very light plastic ball instead of the metallic ball. Same question was asked, and we got the same result. The reason is same, too. The cart and the ball have the same horizontal velocity, so the distances they move are the same.

3) Discussion 3: According to the situation above, more information was given. The cart is moving horizontally at a velocity of 1 m/s. The ball was given a velocity of 2 m/s by the ball shooter. After how long will the ball fall back into the cart? Answer was 0.4 s.

4) Discussion 4: Add acceleration to the cart in the situation above. Where will the ball fall off at? In front of the cart, behind of the cart, or into the cart? Answer was behind the car. The reason is the velocity is changing to be bigger, but the velocity of the ball in horizontal is staying constant. Therefore, in a same amount of time, the cart moves farther than the ball does.

5) Discussion 5: A box A weights 850 g was placed on the floor and with a box B weights 650 g placed on its center top. Friction between box A and B is 0.49 and 0.325 between box A and the floor.
-Draw 3 free-body diagrams for A, B and the whole system.
-Try to find the minimum force that can make the whole thing start moving. It was about 14.65 N.
-How much force do we need to apply to box A then box B will start to slide off?
-After how long will the box B fall off from the edge of box A? It was about 0.44 s.

Lab for “Force and Motion” was started at about at 20:35.
-We use video camera to measure the acceleration of a cart while pulling by a cord with heavy mass at the other end.

It was a funny Lab and it was a interesting class.

Hopefully my summary will be useful. Professor Mason, could you please correct my mistake or fill up anything that I forget to put in? Thank you very much!


Ching Han

Forces and Vpython Graphs

Hi Folks,

I didn't assign anyone to do the blog this time which means I am stuck doing it myself!

We started looking at Newton's first law and explored a problem with a balloon inside a large clear plastic box. Groups predicted how the direction of motion of the balloon would compare to the acceleration of the box. There were fixed results, but after performing the experiment it was discovered that the balloon moves in the direction of the acceleration since the air in the box has some inertia.

I asked each group to list all the types of forces that they could define from physics 2A. We compiled a list of 8 or so different forces.

From there we reviewed freebody diagrams, looking at a problem where a box was supported by a cable and an applied force applied normal to the cable.

Here is a link to all the forces notes for this section: http://physics.mtsac.edu/4A/4A%20Text/Forces.doc

We went through the analysis of the problem and then worked through the pumpkin problem. Finally we looked at the Pre-Lab question of how the vertical displacement of a cord depended on the distance between the points of attachment and the applied masses.

Students spent some time taking data on the vertical displacement and looked at both the small angle region and the large angle region. In the small angle region L is much larger then y so the sin (O) = tan (O) = O. This approximation lets us right down a fairly simple expression for the displacement. In the absence of the small angle approximation more algebra is required.

After working through the lab we spent the last hour talking about using Vpython for graphing.

Here is the handout I showed in class:

Additional Features in Vpython:

Controlling One or More Visual Display Windows

Initially, there is one Visual display window named scene. Display objects do not create windows on the screen unless they are used, so if you immediately create your own display object early in your program you will not need to worry about scene. If you simply begin creating objects such as sphere they will go into scene.

display() Creates a display with the specified attributes, makes it the selected display, and returns it. For example, the following creates another Visual display window 600 by 200, with 'Graph of position' in the title bar, centered on (5,0,0) and with a background color of cyan filling the window.

scene2 = display(title='Graph of position', width=600, height=200, center=(5,0,0), background=(0,1,1))

Now we will start by adding a few additional features to your bouncing balls

program from last week. Open up your bouncing ball program from last week.

Some of the most useful commands for controlling the window in the display are as follows:

center Location at which the camera continually looks, even as the user rotates the position of the camera. If you change center, the camera moves to continue to look in the same "compass" direction toward the new center, unless you also change forward (see next attribute). Default (0,0,0).

If in the loop you set:

scene.center = ball.pos

The ball will always be in the center of the screen and the box will seem to move around it.

autocenter scene.center is continuously updated to be the center of the smallest axis-aligned box containing the scene. This means that if your program moves the entire scene, the center of that scene will continue to be centered in the window.

If in the loop you set:

scene.autocenter = 0

The scene will stop autoscaling.

Mouse Interactions

Mouse objects are obtained from the mouse attribute of a display object such as scene. For example, to obtain mouse input from the default window created by Visual, refer to scene.mouse.

Inside your loop, add the following code:

if scene.mouse.clicked:

mouseevent = scene.mouse.getclick()

sphere(pos=mouseevent.pos,color=color.red)

If the mouse is clicked, generate a mouse event and create a sphere at the position where the mouse was clicked. This will create a series of red spheres over yo

ur program.

A mouse object has a group of attributes corresponding to the current state of the mouse. It also has functions getevent() and getclick(), which return an object with similar attributes corresponding to the state of the mouse when the user last did something with the mouse buttons. If the user has not already done something with the mouse buttons, getevent() and getclick() will stop program execution until this happens.

The following are useful commands for use with the mouse.

pos The current 3D position of the mouse cursor; scene.mouse.pos. Visual always chooses a point in the plane parallel to the screen and passing through display.center.

button = None (no buttons pressed), 'left', 'right', 'middle', or 'wheel' (scroll wheel pressed on some Windows mouses). Example: scene.mouse.button == 'left' is true if the left button is currently down.

pick The nearest object in the scene which falls under the cursor, or None. At present only spheres, boxes, cylinders, and convex can be picked. The picked object is scene.mouse.pick.

Now we will see how to create graphs in Vpython:

Importing from visual.graph makes available all Visual objects plus the graph plotting module. The graph is autoscaled to display all the data in the window.

At the top of your program add the following lines:

From visual.graph import *

graph1 = gdisplay()

funct = gcurve()

This will setup a separate graph window and a function to graph your data.

Inside your loop add the code:

funct.plot(pos=(t,ball.pos.x))

This will plot your ball’s x position as a function of time on the graph you just created.

A connected curve (gcurve) is just one of several kinds of graph plotting objects. Other options are disconnected dots (gdots), vertical bars (gvbars), horizon

tal bars (ghbars), and binned data displayed as vertical bars (ghistogram)

For homework I assigned some mastering physics problems from chapter 4 and 5. (You might read these chapters if you want additional review) At this point we are only working on static situations.

I also asked you to write up a pre-lab on our first dynamics lab. (The cart pulled by a mass)

Finally, I need to see pictures of your cars! Here is a fine picture from Carlos S.

Our First Quiz - 3/6/2008

The first set of Thursday quizzes was given in the beginning of class. We were given 10-15 minutes of class time to finish up until it was collected. Groups were then assigned by listing natural disasters alphabetically.

• Avalanche (I think)
  
• Blizzard
• Cyclone
• Drought
• Earthquake
• Flood
• Gamma ray burst
• Hurricane

After the groups were assigned, we started on our 3rd lab for the semester. The lab was Motion on a Level Surface with an Elastic Cord. Basically a cart is set on a track and an elastic string is attached. One person holds the end of the string at the end of the track and another pulls on the cart to extend the string to about a meter. Using Logger Pro, a video is recorded when the person holding the cart releases the cart to have the cart speeding down the track. Data and measurements are recorded to analyze how the cart behaved during different acceleration and velocity periods of time.

Professor Mason explained also how to set the X and Y positions in the video if the video was recorded in a slanted position. This was important because the graphs can show incorrect data plots and can ruin curve fits.

In the last 1.5 hours class time, we were to work on the basic structure for our car project with the original groups. Professor Mason demonstrated how his car performed using the mouse trap to propel it down the hallway but not back.

Near the end of the class, over half of the groups already have built a car that rolls.

Can the groups develop a car that moves forward and back with near zero displacement in two weeks?

Stay tuned for the next Physics 4A class...

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"