SciHawks

Physics - we continued work on our Dyamics/Forces packet.
We used problem-solving skills to properly set up and solve inclined plane, free-body force diagram problems in Forces 3.

AP Chem- took our unit exam on gas laws and stoichiometry.

AP Chem students take exam under duress!

AP Chem and Physics: good thing- the Blackboard glitch was repaired so files from today are currently being uploaded.

Physics - the HW is to do question 8 of the Forces 3 worksheet.
Today, we did the most challenging problem of the year. Drawing a free-body diagram of an object on an inclined plane. Part of the difficulty is in resolving the weight of the object into its components that are parallel and perpendicular to the incline plane. The other difficulty is seeing that the normal force is LESS than it would be on a flat horizontal surface because the normal force will equal ONLY the VERTICAL/perpendicular to the inclined plane component of the object's weight. Also, for a non-accelerating object, the FRICTIONAL force will be equal and opposite to the horizontal/parallel component of the object's weight.
It will take some practice to be comfortable with these more complex setups. We will also do some problems where the object actually accelerates down the inclined plane.

AP Chem- further discussed the experimental evidence with EMR that led to the Bohr model of the atom.

In AP Chem, the last posted practice test, without the answer key, has an ERROR in question 5.
The reaction is between potassium carbonate and NITRIC ACID (not aluminum nitrate)!
The other information is correct.
7PM - that file has now been corrected.
See yesterday's post for a list of question types on tomorrow's test.
Practice writing your explanations and doing more practice problems.

Physics - we reviewed some of the Dynamics 2 questions.
We introduced frictional force by defining it and then discussing its CAUSE.
We then showed that its magnitude is determined by a COEFFICIENT of friction times the NORMAL/PERPENDICULAR force to the surface that the object is on.
We will apply this concept, which constantly occurs in daily life (you couldn't WALK without a frictional force propelling you forward!).

Physics- we reviewed all three of Newton's Laws, and then we applied these laws to the questions in the Dynamics 1 and 2 dittos. Check your work vs. the notes on Blackboard.
Remember, the acceleration experienced by an object is ALWAYS in the direction of the NET force that is acting upon it.
We also noted that, though each action-reaction pair have equal and opposite forces, the EFFECT of one of the forces on the other object in the pair can be drastically different (bullet force on paper vs. paper force on bullet).

Physics - reviewed the major common errors on the Projectile Motion exam.

The OVERALL error is trying to invent either longer, inefficient, and incorrect ways to solve a physics problem or trying to invent shorter, insufficient ways to solve a physics problem.
Just do the problems EXACTLY as they are solved and explained in class! If there were a better or more fool-proof way to solve these problems, THAT is the way that we'd be doing the problems!

ALWAYS START WITH A PICTURE and then USE THE PICTURE as you label it, and reason through what is going on in the question. As seen in the picture above, you can play around with projectile motion software at this site: http://www.goldenkstar.com/projectile-2d-motion-mechanics-physics-software.htm

In any WRITTEN-response test, you get credit for any answer ONLY IF you show SUFFICIENT work to support your answer. Generally, writing any answer, correct or incorrect, will not get you any credit. It's even worse to write a correct answer with no work shown because that SUGGESTS copying (though I don't get a general indication of that from our upstanding class).

When calculating the angle of launch or crash, you must find the vertical and horizontal components of VELOCITY, not distance! You then label those components as opposite and adjacent to the angle relative to the horizon, respectively. You then take the inverse tan to get the angle.

We did Dynamics 1, problems 3 and 4. Check your work with Blackboard for the answer to 4.

Physics- we discussed Newton's 2nd and 3rd Laws.
The second law relates the NET FORCE/UNBALANCED FORCE as the cause of the ACCELERATION of an object; how much acceleration that is experienced by the object due to a given force depends on its INERTIA/MASS. Quantitatively, the relationship is
 Force (net) = Mass x Acceleration

The third law, which will make more sense when we talk about the law of momentum, is that there is an equal and opposite reaction/force to every action/force AS LONG AS the action reaction pair is NOT ON THE SAME OBJECT i.e. the action/reaction pairs MUST be on two different objects for this law to hold true.

AP Chem- our Gas Unit exam will be given next Wednesday or Friday, depending on class academic performance. When you come to class, immediately take out your notes and review them; have questions prepared, and immediately copy anything that I have written on the board/screen. We must be much more efficient, otherwise our class performance and our class schedule will be of substandard, instead of the assumed excellent quality that is required of this course.

we finished the discussion of the gas laws by explaining that adding another gas to a container will increase total pressure but will NOT affect the collision frequency and force (i.e. partial PRESSURE) of the OTHER gas or gases already in there.



We then derived Graham's Law of Effusion/Diffusion by considering the mathematical formula for KINETIC ENERGY. At a given temperature/average kinetic energy, the greater the molecular mass of a molecule, the slower its average velocity, thus the lower its rate of effusion/diffusion. We then applied the formula to compare the relative rates of effusion of two different gases.
 
We had a detailed discussion of what CAUSES pressure in a container of a sample of gas. By focusing on the 1. pressure causing collision frequency of the gas particles with the container wall and 2. the pressure causing kinetic energy/force of the collisions, we can explain/reason any of the gas laws.
 
Check out the animation of the gas laws on Blackboard, as well as the thoroughly written explanations posted in the notes from Friday. 

Physics- began our new unit on Dynamics, in which we will study the laws that relate Force to Mass to Acceleration.
These laws were discovered and mathematically quantified by Isaac Newton, one of the all-time genius scientists whose impact on the world is still felt every day.

We discussed his description of the relationship between mass and "inertia", which is the RESISTANCE to change in velocity. An object that has a lot of MASS will naturally have a lot of resistance to changing its speed and/or direction, whether that mass is at rest or moving.

AP Chem - we did a Dalton's Law of Partial Pressure/Ideal Gas Law problem involving a gas collected over water, a process that automatically introduces water vapor as one of the gases contributing to the total pressure.



We then did a gas stoichiometry problem involving a conventional "two-bulb" setup in which the gases are initially separated, each with unique conditions, and then combined and (usually) reacted.


I will post MANY review problems with fully detailed solutions.

Physics - took part II of our Projectile Motion exam.

AP Chem - Did a Dalton's Law and stoichiometry problem in which a gas was collected over water, a process that automatically introduces water vapor as one of the gases contributing to the total pressure.



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Physics - took the multiple choice part of our projectile motion unit exam; tomorrow, we will have the written-response part of the exam during the first period of our double.

AP Chem- The hydrated salt lab write-up is due on Friday. Make sure that all work is explicitly shown in detail for all calculations, and that all answers/explanations are drawn/written in complete sentences in explicit detail.

We continued the gas laws solving for the molar mass of a substance given its temperature, pressure, volume, and mass (while it is in the gas phase).

We then discussed two versions of Dalton's Law that show pressure and mole relationships in a mixture of gases.
We aslo did a Dalton's Law of Partial Pressure/Ideal Gas Law problem involving a gas collected over water, a process that automatically introduces water vapor as one of the gases contributing to the total pressure.
See Blackboard for more practice with this.

Physics - I just posted a MAMMOTH multiple choice DETAILED answer key to our projectile motion multiple choice questions at the end of the packet. See Blackboard.
Do the questions first, timed. Check your answers versus my answer key.
Check that you solved the problems efficiently, and that you used test-taking skills, drawings, and logic.

For the written-response exam on Wednesday, I will post the remaining written-response answers to our projectile motion packet questions.

Today, we finished up the data analysis and questions to the vertical projectile motion/tennis ball lab.
Note how important that visualization, labeling, and drawing pictures are to properly solving a physics problem. Most of the "hard work" of physics is just drawing and labeling what is going on in the question. After that, you are just plugging in numbers for variables.
:)
We began our "projectile launched at an angle lab" by throwing baseballs and gathering the time of flight as well as horizontal distance/range data.

Study hard for the multiple choice exam tomorrow; email me if you are confused, or better yet, come to extra help in Room 306 at 8AM tomorrow so that we can do some problems.

Physics - did a projectile motion demo with our infamous spud-gun :)

We saw that the MINIMUM data that needs to be collected in order to determine the initial launch velocity (and angle, even though we set the angle to 60 degrees in this demo) is the RANGE, horizontal distance, and the TIME of flight. We assumed a flight time of 1.20 seconds, but next time we'll get an average time and range from three or more trials.

We then worked on projectile motion 2 question 3, which shows us how the range of a projectile varies with launch angle. The range increases with increasing launch angle UP TO 45 degrees, but then the launch angle decreases proportionally until the projectile is fired straight upwards, at 90 degrees, so the horizontal range goes back to zero meters.

Check Blackboard for the assigned HW, which I will check on Monday morning:

Finish Projectile Motion 2, question 3c (I'll post the answers with work show to question 3a, which we almost finished in class, and to 3b and 4, as a reference for you.
Then do Projectile Motion 3, question 5; (I'll post the answer to question 4)

Projectile Motion 4, questions 1 and 2 (we already did question 3)

Projectile Motion 5, questions 1, 2, and 4.( I'll post the answer to question 5, we already did question 6, the same as Motion 4, question 3) .
 
AP Chem - took our Stoichiometry/Solutions exam- 150 points. Clearly, most of you prepared more for this test, and seemed to report that this test was "easier", though from an information-required perspective, this test was more challenging.

Physics - we separated the projectile motion problems into two types: 1. objects launched horizontally which the fall "freely"/accelerate towards Earth due to gravity.  2. objects launched upwards at an angle to the horizontal, which then travel in a parabolic path as they are accelerated towards Earth due to gravity.

In the 2nd problem type, the velocity vector has to be resolved into its vertical and horizontal components.

We reviewed the hw questions (thanks for catching the two errors! I didn't write the equation/look at the picture to see that my answer only considered HALF of the total distance and HALF of the total time!)

We practiced using the projectile motion organizer, and showed the data that can be consistently
"pre- entered".

We then discussed the tennis ball vertical motion analysis lab, which we will continue on Monday.

AP Chem - NOTE: on the last practice test file, question 5 is a mixture problem in which BOTH parts of the mixture react with another reactant; in class, I stated that these questions are now considered too complex for the AP exam. We will do these questions after the AP exam, so do NOT worry about them for tomorrow.

Tomorrow's exam will have:
1. the four gas-forming reactions (as well as the two types of previously tested double replacement reactions)
2. redox balancing via the half-reaction method including identification of oxidizing agent and reducing agent
3. stoichiometry (from mass) with limiting reactant, and percent yield
4. molarity calculations
5. making solutions, and dilution calculations
6. solution stoichiometry/titration (acid/base or redox) to determine the percent composition of a given element or compound in a mixture/ore or to determine the empirical formula of an unknown acid
7. solution stoichiometry with limiting reactant, and FINAL concentrations of all non-spectator ions in solution.


Of course, you MUST by now be EXPERTS on formula writing and naming!
You must be EXPERTS on proper use of units and significant figures (in your FINAL ANSWERS, only).

Physics- the HW tonight is Projectile Motion 3, questions 1 and 2. I'll check your work (work shown, equations, units, unit cancellation, drawings, organizer, etc.) at the beginning of class tomorrow - 10 points.
We saw an efficient and organized problem-solving strategy for projectile motion.
By drawing a simple picture, and organizing the data into two tables (one for each half of the flight), remember AD TVV , we can quickly solve for the unknown variables.

We then collected data for our projectile motion lab.

AP Chem - saw how acid-base titration/solution stoichiometry can be used to determine whether an acid is mono, di , or tri- protic.
We then did one final assay/redox titration to determine the percent of a given element in a mixture/ore.

We began our unit on gas laws and stoichiometry using gas data (P,V,T).

Physics- finished up the graphs and questions on our free-fall motion analysis lab.
We then did question 3 on the Projectile Motion 1 ditto; the answer to question 4 is posted in the notes on Blackboard so do that problem, and check your answer.
We then started analyzing projectile motion of objects that are launched/thrown at a particular angle from the horizontal. We saw that the parabolic path is symmetrical so not only do we analyze the vertical and horizontal components of a, d, and v, but also we separately analyze the "upwards" first half of the trip, and then the "downwards" second half of the trip.
Tomorrow, you will see that the numbers are SLIGHTLY easier for the downward part of the trip because all quantities are positive.

We will go on to gas stoichiometry/ gas laws tomorrow.
PROBLEM SOLVING TIP: if you are unsure what to do in a calculation/problem, take scrap paper and do the SAME problem with VERY SIMPLE WHOLE NUMBERS; then apply the same PROCESS to the more complex numbers in the question.
The same goes for "unknown" formulas: on scrap paper, see how a KNOWN compound's formula would be manipulated to determine its formula, and then do the same PROCESS to the "unknown" compound in the question.

Class performance on the written part of this exam (where you can really demonstrate your knowledge/process) was VERY IMPRESSIVE!
Consistently identified/highlighted variables in the questions, clearly written formulas, properly written units (with cancellation!) yielded great scores.
There was a delay posting your scores to Blackboard but I will try to correct that later tonight.
Keep up the good work as you have just shown and you will continue to improve and even excel in this course!
Thanks!

Just came across a very good and practical physics extra help/homework site:

http://www.physics247.com/physics-homework-help/index.shtml

On this site, there are solved problems (with good graphics and organizers) and quizzes with solutions by topic and subtopic - good for extra practice before each unit exam.

Physics - did two projectile motion problems by methodically separating the vertical and horizontal types of motion in order to solve for time or whatever unknown variables that were needed.
For HOMEWORK, do questions 3 and 4  from that same ditto, Projectile Motion 1; I'll check that on Tuesday, and we'll go over the problems before our lab.

http://www.youtube.com/watch?v=fP64kpomuII

Physics - began our unit on Projectile (TWO-dimensional) Motion. We saw that freely falling objects, whether they are thrown horizontally or just dropped, will ACCELERATE towards the Earth (due to gravitational attraction) at the SAME EXACT RATE (neglecting any air resistance). So, firing a bullet horizontally from a gun, while dropping a bullet alongside the SAME gun, will cause the bullets to hit the ground at the SAME TIME because they are acted on by the SAME gravitational force VERTICALLY downward towards Earth; they will BOTH  be accelerated vertically downward at 9.8 m/s^2. The ONLY difference will be that the horizontally fired bullet will land some far horizontal distance away as it strikes the ground at the same time as the dropped bullet.

We then did used our vector addition knowledge from unit one to combine the vertical and horizontal components of a velocity to obtain a resultant velocity of a projectile that is freely falling, given an initial horizontal velocity (but no longer being pushed horizontally!).

AP Chem - continued our redox balancing process for both acidic and basic solutions.
See Blackboard for massive stoichiometry and redox balancing practice.

Physics - took part two of our straight-line motion exam.

AP Chem- continued our hydrate lab, noting the possible experimental uncertainty of subliming some of the anhydrous salt.
We then did another volumetric analysis problem - check notes on Blackboard for the final answer.

We continued the all-important redox balancing via the half-reaction method.

Physics - took the multiple choice of our one-dimensional motion exam. Tomorrow, we will have the written-response part of the test.

AP Chem - started solution stoichiometry, using the BALANCED chemical equation and conversion of solution concentration and volume to get moles; then we did the typical moles of reaction ratios to get the limiting reactant, quantities of product formed, etc.

Physics- we analyzed the displacement vs. time graph (number V) and answered the corresponding questions. We then did another one-dimensional kinematics problem in which we calculated the time that a ball thrown vertically will take to reach the apex of its path given the deceleration due to Earth's gravity (-9.8 m s^-2).

AP Chem - showed how to make a solution of a given volume and molarity.
Noted the three, sometimes four, parts of the molarity formula.

Derived the dilution formula as based on moles of solute, and then applied the formula.
Continued our percent composition of a hydrate lab.

Physics- our Unit 2 Straight-line motion test will be given next Tuesday (multiple choice) and Wednesday (written response). Our first motion analysis lab is due on Monday (email me if you have questions or hand it in at extra help after school on Monday, where we can go through it to make sure that you get a great grade.

Do the "practice test" questions at the end of our unit 2 packet. Look on Blackboard for detailed answers to the unit packet practice test (at the end of the packet); email me or come to extra help if you have trouble with any of the questions or explanations.

We finished Motion Ditto 4 and then analyzed the speed vs. time graph IV, in which the object moved forward, stopped, and then moved in reverse.

For each of three types of motion scenarios, we sketched side by side, the graphs of distance vs. time, speed vs. time, and acceleration vs. time.

We started our second motion analysis lab in which we will determine the acceleration due to Earth's gravitational force on any object (neglecting air resistance).

AP Chem - we added to our list of reaction types by learning the four classic gas forming reactions.
We continued our lab prep.
By Saturday/Sunday, check Blackboard for a reaction type worksheet and more stoichiometry files.