3/27/2008

Eric cannot find the link to post, so he send me what he wrote and I post for him.

3/27 Class Recap
Hi everyone,
I’m Eric Zhang, it’s my turn to write the blog this time, however, I’m not in the contributors’ list; my name out there is fake(I’ve tried many times to sign in, but it doesn’t work), so I ask Nelson (Ching Han) to use his name to post this words. Hopefully, this last post can still help to you guys to remain the stuff we learned.

1. The class started at a quiz. The problem is about cart collision. According to the force versus time graph, we had to calculate the peak acceleration, initial velocity and total distant; draw two graphs about velocity versus time and position versus time. (be careful of the direction of each vectors)

2. After the quiz, Professor gave us some information about the exam on next Tuesday.

2 problems form master physics
1 problem form Lab
2 problems made up by professor

(Included 1 kinematic, 1 work energy, 3 force)

3. Afterwards, we were introduced to the interesting topic “Superposition” since the theory was discovered the same date (March 27) on 1935. The concept of superposition helped provoke Schrödinger's conjecture, which is the combination of all the possible positions of a subatomic particle. The principle of superposition states that if the world can be in any configuration, any possible arrangement of particles or fields, and if the world could also be in another configuration, then the world can also be in a state which is a mixture of the two, where the amount of each configuration that is in the mixture is specified by a complex number. The theory has succeeded in applying to quantum computer.

4. After making group by 2^n, we worked on the first problem “Work done by a variable force”. We were remained the changing force acted by a spring, and then we calculated a non-hookian spring problem.

5. We were introduced a new theme about power (watts), Power=Changing Energy/time; Power=Work/time; Power=Force*velocity. 1hp=746watts. Furthermore, professor explained the idea of power in terms of solar output used by human.

6. Continuing our typical white board problems, we focused on power practices with air drag. There are “Air Drag on a Bicyclist” and “Constant Powers Bat-Engine”. (It is very hard to combine power and calculus together)

7. After working through the problems, we spent the last half hour on using Vpython. Similar to our project, the new introduction is about how to make a virtual car go forward then come back with acceleration.
This is the code copied from Professor.

from visual import *

wheel1 = sphere(pos=(.1,0,0), radius = 0.05,ccolor = color.red)
wheel2 = sphere(pos=(-.1,0,0), radius= 0.1, color = color.red)
body = box(pos = (0,0,0), size=(0.2,0.05,.2), color = color.green)
floor = box(pos =(0,-0.05,0), size = (5,0.01,0), color = color.blue)

scene.autoscale = 0

body.velocity = vector(1,0,0)
body.aceleration = vector(0,0,0)
dt = 0.00001
t=0
while (1==1):
rate = 100
t = t + dt
body.pos = body.pos + body.velocity * dt
body.velocity = body.velocity + body.aceleration * dt
wheel1.pos = body.pos + vector (0.1,0,0)
wheel2.pos = body.pos + vector (-0.1,0,0)
if t<0.5: aceleration =" vector(2,0,0)">0.5:
body.aceleration = vector(-2,0,)
if t>1:
body.aceleration = vector(-2,0,0)

Ok, that’s all we done on March 27, welcome everyone make comments to add whatever I missed or correct any of my mistakes.

At last,
Best wishes for Professor Masson can get well soon.
Hope everybody get a satisfying grade on the first exam.
Thanks for reading.

Eric Zhang