Celebration of Knowledge Strikes Back

This will be short and isn't meant to be like the crazy blog entry I have done before.

Anybody who encounters this blog entry can comment:

Was the 2nd exam difficult? Your opinions and thoughts are welcome to the table.

• Energy was overlooked.
• Different CD scenario problems to study was also overlooked (most got wooped).
• My 3x5 card with equations was utterly useless.
• One problem was similar to the Geosynchronous Satellite in Mastering Physics.
  
• In the cart problem, I thought Brian should have been replaced with "Rutherford"(say it like Roy would) (nothing against Brian).
• My extra credit was a surprise but won't save me from my inevitable demise.

Comments people! A decent productive blog entry would be great too. I'm not a regular blogger, but its cool to read something instead of me typing stuff out of my head.

Message for Tong Li

Hey all, could you help me contact Tong,

This not Gabby; this is Ben ... need to confirm with you on JPL.

Is this your legal name: Tong Li

JPL will be on April 25th, Friday afternoon ... so you are free?

It is a high security tour: If you are U.S. citizen, you would need to show a gov't issued ID, or driver's license.

(school ID not accepted)

If you are a green card holder or legal resident or international student, you need to show your green card or Visa or Passport.

Please email me ASAP at: sps.4t.s4c@gmail.com to confirm .... or I'll have to pass down the spot...thanks...

Someone has to write this...

Since nobody is doing the blog and I am contemplating what to do tomorrow, I'll write a quick version of what happened today.

Since Professor Mason is off in Arizona somewhere doing something Physics? related, Professor Christensen was kind enough to sub in until his 7pm Physics 2A class. After the short introduction, we began our wonderful "mini-celebration of knowledge" as it covers over the center of mass momentum.

Paraphrasing from my memory, the first question asked how far would the fisherman move if he tied a string to his cabin's door knob and pulled on a frictionless ice lake.

• Fisherman - 80 kg
• Log Cabin - 250 kg
• Distance in between - 10 m

Using the center of mass of a system defined as the average of their positions , weighted their masses m_i:

Basically you take ((80*0)+(250*10)) / (250 + 80) and we should get around 7.58 m since we treat the fisherman as the origin.

--------------

The second problem had 6 parts to it involving a desperate fisherman applying his momentum force onto the cabin to save his hide.

A frustrated ice-fisherman with a mass of 80.0 kg and his 250 kg fishing cabin are sliding together across a frozen, frictionless lake towards thin ice at a speed of 1.60 m/s to the left. The cabin is ahead of the fisherman. Upon seeing the "thin ice" sign, the frustrated person pushes against the cabin for .300 seconds, giving himself a velocity of 32.0 cm/s in the opposite direction.

1. What is the magnitude and direction of the total momentum of the person and the cabin after they separate?
2. What is the speed of the cabin after they separate?
3. How much average force does the person exert on the cabin?
4. How much work did the person do on himself and the cabin in order to give himself a velocity of 32.0 cm/s in the opposite direction?
5. What does a fishing cabin become when it is surrounded by molecules of H₂O at 10.0^o C?

So we have our givens:

mp	= 80.0 kg	(Mass of the person.)
mc	= 250 kg	(Mass of the cabin.)
vo	= 1.60 m/s	(Initial velocity of the person and cabin.)
vp	= .320 m/s	(Final velocity of the person.)
vc	= ?	(Final velocity of the cabin.)
tp	= .300 s	(Time the person pushes.)
Wp	= ?	(Work done by the person.)
Fave	= ?	(Average force exerted by the person.)

Quick rundown:
1. Conservation of momentum - Final momentum must equal to Initial momentum
(250 kg+ 80 kg)(1.6 m/s) = 528 kg*m/s or N*s

2. Again, conservation of momentum
((250 kg + 80 kg)(1.6 m/s) + (80 kg)(0.320 m/s)) / 250 kg = 2.21 m/s

3. The impulse exerted on the cabin is equal to the average force multiplied by the time
(80 kg)(0.320 m/s +1.6 m/s) = 153.60 m/s

Force avg = Impulse / Time so 153.60 m/s / 0.300s = 512 N

4. Avg Work = Final KE - Initial KE or
(0.5)(250 kg)(2.21)^2 + (0.5)(80 kg)(0.320 m/s)^2 - (0.5)(250 kg + 80 kg)(1.6 m/s)^2
612.94 J + 4.096 J - 422.40 J = 194.64 J or 195 J

5. ......
Wet!

Or refer to Mason's Momentum notes.

After the quiz, Christensen gave us an explanation of kinematics in class about rotational kinematics which uses the same kinematics that we learned in 2A. Or refer also to Mason's Rotational Kinematics notes.

Note: Tomorrow - 4/18.... sigh.

Do I really have to do this...

Hey everyone this is Keith and i guess its finally my turn to do the post thing.

SOOOO, lets see if my memory serve my correctly as I recap on what we did today.

We started class with a quiz, and here are the questions on the quiz.
1)Calculate the velocity of planet mar. sun m=2*10^30, Earth m=6*10^24, Mars m=6.4*10^23, and Mars circle the sun once every 1.88 Earth year. The answers is about 2.4*10^4 m/s
2)Calculate the velocity of the Earth. The answer is about 3*10^4 m/s
3)Calculate the velocity a satellite need i order to stay in a constance orbit 200km above the Mars Surface. The answer was B) about 1000m/s when rounded into one significant figure.
4)Draw the graph of how the Mars and Sun effects the velocity of the satellite. the answer could be a constant or it could look like a mini sin graph.

Then my memory got a little fuzzy and i don't recall if the Newton's Cradle or fun-doh cart came next. I guess the Newton's Cradle is next.
Professor Mason showed the class a Newton's Cradle and presented a question.
If one of the steel ball is replaced with a aluminum ball(less mass), will the system work or will it falls apart.
It turns out the system fail because the Newton"a cradle conserve both the momentum and kinetic energy. Steel ball have the mass or M and the aluminum ball have the mass of 1/3M. When the first steel ball hits the second steel ball, momentum and energy both are transfer perfectly. But when the steel ball hits the aluminum ball, 1/2mv^2 transfer to 1/2(1/3M)v^2. The equation fails and the system falls apart. So the mass have to be the same for the Newton's Cradle to work.

Professor Mason showed us a cart hitting a hard object comparing it hitting a softer object. The difference were that if it is against a hard object, force will increase very much in a very short amount of time. When the cart hits a softer object. The force is less and it is spread out in a long time interval.
Then professor showed us a sample of in an event of aircraft failure, what should you do????
-I choose to use a parachute which greatly increased the time interval before the impact.
-Edward chose the potatoe factory, which after he fall through the roof, the smashing of the potatoe will increase the time before impact.
-The next classmate(sorry i forgot his name) chose the water. But when an object hits water above 25mph, its like hitting brick wall. SO..... he didn't survive the fall. =[
-Eric chose the tree which can potentially save his life. Professor mason then told us a story about how a female flight attendant survived the fall from 30000+ft when she hits a tree and broke quite a few dozen bones but she survived.
-Chris was next and he Chose the snowy slope. Then professor mason told another story about how a British pilot during WWII survived a fall from 7000ft by aiming at a snowy hill. He only broke one bone but after he landed he was POW for 2 more years.
-Max was last and the only place left was the concrete road. Well at less its quick right?

Then professor Mason continue talking about momentum and the change in momentum. He introduce the change in momentum is Impulse.
F=ma
F=m(dv/dt)
Fdt=mdv

Then professor Mason showed how a satellite orbit goes around the moon and lands on earth, like Apollo 13 flight orbit. But the moon orbits around the Earth also, so we need to launch the rocket at a certain angle from the moon initial position and but the time the rocket reach the moon, it should the moons orbit should be in the rocket's path. Professor Mason also explain how the miscalculation of china shooting down its satellite increase the space junk. Poop is also a type of space junk. For our next project we need to design a flight plan to shoot down an orbiting satellite while avoiding all the space junk.We were assigned to our new group.

Then there was the long needed break. And the remaining group present their project while the rest of us worked on the Apollo vphython.

Hi guys, I am Frank.Today, it is my turn to write up the blog

The class started at a question about curvilinear motion. From the question, we can know the velocity has vector, and it can divide in two component which is x-axis, y-axis. Then, we talked about the one of the previous test problem, and we redo it, and had a deeper analysis. We made the graph of falling object in six graph, which is acceleration on xy axis, velocity on xy axis, and position on xy axis. From the graph, we found the acceleration on x-axis is constant. Then we calculated some number which Professor Mason asked we do.

Then we did a question about crossing river. To solve this kind of problem, the connection is Time! Don't forget it.

Next topic we talked about is centripetal force. Of course, we could know the object is doing in circular motion. We did some reviews from Physics 2A.

Fcentripetal=(mv^2)/R

Acceleration=(V^2)/R

When a string tie a object, and it is stayed. We could know the object has weight and Tension force. But, when it is doing in circular motion, it has centripetal force!!! At this time, the equation could be:

T=W+F

When the object at the bottom, the Tension force will be largest.

After we finished talking about the lecture, Professor Mason give us rest of class to improve our mouse trap cart, and we also need to collect the data of the mouse trap. We used Loggerpro to record the video of cart moving by mouse trap, and calculate the acceleration, then, we need record the video of cart moving by mass, and get the another acceleration. With two acceleration, we can make a model in our Vpython.

That's all we did on April 3rd. On coming Tuesday, and Professor Mason will pass back the exam which we took on last Tuesday, and Professor Mason will pass back lab report either. The mouse trap cart also due on Tuesday, and we will test the result on that day. To get a good grade in the project, please following the form which Professor Mason post on April 3.Probably, we need show the presentation and Vpython on that day! Guys, please prepare for our first object, and get ready for our next project because Professor will give out the second project at same day.

At last,
Hope everyone get a satisfying grade on our first project.
Thanks for reading

Frank Mao

4-1-08 1st CELEBRATION OF KNOWLEDGE

EXAM TODAY!!!

On Tuesday you had the opportunity to experience your first 4A exam! 2 and 1/2 hours of pure physics joy! You wrapped your brain around conundrums about the critical angle for pushing a lawnmower, interpreting velocity graphs for a cart on at track, stacked crates on a pick up truck with a tilt bed, the many joys of a firepole which has a position dependent frictional force and finally dropping packages out of helicopters with air drag! Smiling and laughing you trooped out of class! (Only a few of you in whitecoats and straitjackets!)

NOTE: The last problem on the Mastering Physics for Tuesday is TOUGH! Plan some time for it!



Here is a copy of a rough draft of the rubric I will use for grading your projects:

Project 1 Grading Rubric

Group Members _________________- ___________________-___________________

Objective	Score	Weight	Total
Was there a video of the car going out and back?	0 1	2
Do the students have data from the video?	0 1	2
Does the program have a visualization of the car going out and back?	0 1 2	2
Is there a discussion of the mission design?	0 1 2	2
Is the data from the video used to determine the motion of the car in the program?	0 1 2	3
Is there a robust model for the motion of the car?	0 1 2	3
Is the output from the computer model compared with actual measurements?	0 1 2	3
Is there a discussion of kinematics, forces, work energy and any other physics considerations?	0 1 2	2
Does the Calculated range match the measured range? >50%, 30-50%, 10-30%, <10%	0 1 2	2
Are there six graphs of the kinematics quantities?	0 1 2	3
Are the internal details of the computational model explained clearly?	0 1 2	3
Calculated distance Out?	Measured Range Out?	% Difference
Project does not run or runs minimally. There are many technical problems when viewing the project.	Project runs adequately with minor technical problems.	Project runs perfectly with no technical problems. For example, there are no error messages.
Project has multiple errors in spelling and/or grammar. (Four or more errors)	Project adequately honors most rules of spelling and/or grammar. (Two or less errors)	Project honors all rules of spelling and/or grammar.
Project is incomplete and contains some unfinished elements.	Project is incomplete and contains several unfinished elements.	Project is completely finished.
The work is a rehash of other people's ideas. There is little evidence of new thought or inventiveness.	The project shows some evidence of originality and inventiveness. While based on an extensive collection of other people's ideas, the work extends beyond that collection to offer new insights.	The project shows significant evidence of originality and inventiveness. The majority of the content and many of the ideas are fresh, original, and inventive.
Little evidence that higher level thinking skills were used in the creation of this project.	Some evidence that higher level thinking skills were used in the creation of this project.	Clear evidence that higher level thinking skills were used in the creation of this project.
Some subject knowledge is evident. Some Information is confusing, incorrect, or flawed.	Subject knowledge is evident in much of the project. Most information is clear, appropriate, and correct.	Subject knowledge is evident throughout the project. All information is clear, appropriate, and correct.

Good luck on finishing your projects for Tuesday! Remember:
Vpython Code
Google Docs presentation
WORKING CAR!!!


have fun!