This'll just be an introductory meeting. We'll read from the lab book, because you are all gradeschoolers, and then I'll give some words of inspiration which can be distilled into this FAQ.

By the way, you will probably want to check out WebCT/Vista which is here. This is where all the grades will be posted and where you will do your prelabs.

• Force Equilibrium, most specifically the Law (which one?) that (1) corresponds to. Note that this will get slightly more complicated later.
• Resolving a vector into components. A necessary step for the above process. See equation (2) through (5) for a quick review. If you want a little math practice, try proving either set of statements from the other.

• Make sure that the ring is centered around the peg for best accuracy, essentially, when you remove it, it should stay stationary.
• Don't forget to zero your balance. Either zero it manually, or take a zero reading and subtract it off.
• Your calculator lies! Well... some of the time, anyway. When doing the inverse tangent (or arctan) keep in mind that it only gives you the primary values of the argument. What does that mean? Check your signs, and make sure that the direction you give makes sense.
• Checking two force equilibrium is just that... there is one way and one way only to achieve equilibrium with two forces. Think about it.
• Vectors have two things: magnitude and direction ensure yourself that when you answer with one that it has both.
• Active phrase of the lab? "Equal and Opposite!". Learn it, love it, it will take you far
• In a jam, google not only serves as a calculator but a radians/degrees calculator.

• Vector Calculator - Try this out to see how vectors are graphically added.
• Science World's entry on Weight - Get familiar with the concept, you'll be using it, and you might be surprised that it's not a constant.

Okay! With the benefit of hindsight, let's review what we learned this week, shall we? Here's a list of things to work on in the future:

• Vector components have units. They're the same units as the vector. Watch your units in general.
• Make sure you're answering
  all the questions. The quickest way to lose points is to not answer a question.
• Let me repeat this one more time so everyone can see a hardcopy. There are three buzzwords on these labs:
  1. Compare - This always means writing down the two pertinent numbers and giving me a difference. I never want to see "they were relatively close". 1 is relatively close to 100 when you consider all the numbers between 1 and a million, but that doesn't mean its close for your purposes.
  2. Calculate - Give a formula and the numbers you used for it. Simple.
  3. Explain - Give me a few sentences describing concisely and exactly what you observed. Avoid using general pronouns like "this" and "these" because I need you to be specific. "This vector" and "that vector" all look the same to me.
  

So, after the scolding, let me congratulate you on picking up the main concepts pretty well. I went light on most of you this time around, so don't get into the comfort zone on these grades. Speaking of which, here are the distributions:

• Section 5001
• Section 5007
• Section 4990

• Velocity is the change in position divided by the change in time. See equation (1).
• Velocity is therefore, the slope of the position graph.
• Slope intercept form of a line. Equation (2). You'll need this because the concept of slope and intercept are important for this lab.

• The sensors work by soundwaves. You'll mess up each others experiment if the tracks are exactly aligned.
• Make sure you read the section on how to work the program carefully. If you don't, you'll end up spending too much time trying to calibrate and use it.
• If all else fails, restart the program, and then if nothing else works, restart the computer.
• There is a difference between a flat line (one with zero slope) and a straight line (one with non-zero slope).
• Equation (3) is not valid. If you want to know why, either ask me, or check a book on calculus.
• Don't describe a slope that's changing with time as "exponential" or "quadratic". Simple describe how the slope changes with time.
• When you calculate the slope, make sure the time interval is appropriate for the space interval you're calculating.

• The difference between distance and displacement - One is a scalar, the other is a vector. Knowing the difference helps in tests.
• Interactive demonstrations - Go here, and try out problems 8.1.1, 8.1.2, and 8.1.ap2.

What did we learn!?

• Averaging over the period 0-5 works only if the velocity is constant. You had to pick an interval where the velocity was constant else your averages will have differed greatly.
• The "straight" vertical lines correspond to instantaneous acceleration. Physically impossible, but that shouldn't mislead you from the fact that if the position graph is horizontal over an interval, its velocity graph is zero there too.
• Listen, if the numbers don't jive, then you're not attempting to understand the physics behind the experiment. Numbers should match up, it's a check on what you're doing.
• Watch your units/numbers conversions. I was nice this time. Please be more careful or it'll hurt you in the future.
• If you can calculate something, do it! It's usually not hard.

• Acceleration is the change in velocity divided by the change in time. See equation (1).
• Acceleration is therefore, the slope of the velocity graph.
• The only change from last lab is now, the position graph has a curve to it which we can in fact quantify as quadratic. See equation (2).
• Quadratic form of a line, equation (2b).

• Parts 16, 17, and 18 are out for your benefit and mine.
• Review your manuals on how to work the program. Also remember how to calibrate the track, you're going to be doing it a lot this semester.
• The acceleration will always be a fraction of gravity in this case, but the force of weight isn't the car. Think about that.
• Watch the pullies, it doesn't take much for the string to get pulled off the rim into the axle and change your resorts.

• Does a good overview of constant acceleration.
• The famous monkey and the hunter demonstration - This is the granddaddy of constant acceleration brain teasers.

What did we learn!?

• If a question asks you to do something, make sure you do it, instead of answering part of it and moving on.
• Non-zero launch velocity corresponds to a higher intercept on the v vs t axis.
• COMPARE = RELATIVE DIFFERENCES
• If you can quantify how something changes, and its relatively simple to do so, please do it, because the question probably requires it.
• You'll notice you've started to lose points for units. Next time will be sig figs. Three is the general rule of thumb, zeroes don't count unless they're squished between two other non-zero numbers.

Distributions:

• Section 5001
• Section 5007
• Section 4990

• We've revised the sum of the forces to include acceleration (equation 1)
• Read up on the spring model of intermolecular forces. I'll try to go over it but reviewing it on your own won't hurt.
• Friction is directly proportional to the normal force. If there's no normal force, there's no friction. (equation 2)
• Static friction is dependent on the amount of force you apply. If you apply no force, then how can friction oppose it?

• Don't forget to calibrate the force sensor. It's the tab right next to the track calibration.
• Review how to input and analyze data with excel.
• We're thinking of macroscoping objects as collections of interconnected springs. Think a spring mattress when you do this, only with springs of varying strength.

• Jeff's section on CB for a couple of hints on calibrating the sensor as well as some additional ideas.
• A demonstration of Hooke's law which relates to springs. You'll need this later, but it's a review of how it works for the microscopic theory.

What did we learn!?

• If a question asks you to do something, make sure you do it, instead of answering part of it and moving on. I'm leaving this here, because a lot of people lost a lot of points on things they shouldn't have.
• The third law doesn't describe two forces on an object. It describes an interaction between two objects. F₁₂=-F₂₁. That's a statement that says that if two objects are in contact their interaction is equal and opposite. The normal force is a reaction to the weight. Friction is not a reaction to tension or F_app because it acts on the same object. I didn't mark off for it, but remember it for tests.
• There is a distinct difference between "moving" and "acceleration". One is constant velocity, the other is not. Be careful with your language.
• The inequality matters. It's the maximum of static friction that's greater than kinetic friction. On the whole, the kinetic friction is greater than static friction because of that inequality.

Distributions:

• Section 5001
• Section 5007
• Section 4990

What did we learn!?

• If a question asks you to do something, make sure you do it, instead of answering part of it and moving on. I'm leaving this here, because a lot of people lost a lot of points on things they shouldn't have.
• The table data asked to correlate three things, velocity, acceleration, and force. Force and acceleration are related by Newton's law and the friction. Velocity and force are related because friction always opposes the direction of motion, hence the relative sign change.
• Look for significant features in your graphs. The small wiggles aren't of much consequence, so try to draw the overall picture instead of focusing on each little detail.

Distributions:

• Section 5001
• Section 5007
• Section 4990

• Turns out the Force Law was the "weak" version. The strong version involves momentum. Eqn 1
• The law of impulse momentum (equation 2) is universal and has not yet been broken, be sure to use it
• Elastic collision - one where kinetic energy is not lost.
• Inelastic collision - one where kinetic energy is lost... usually to deformation or two objects sticking together

• Don't forget to calibrate the force sensor. It's the tab right next to the track calibration.
• Review how to input and analyze data with excel.
• Make sure everything is steady and propped up against something, this is important because momentum transfer out of the system is not only possible... it's likely
• We want the least number of averaging points in this lab. This has to do with the resolution of the sensor. Impulse and momentum transfer happen over a few microseconds, so its easy to miss
• Make sure your graphs are expressive. They'll look like a sharp peak around a constant value.
• Yes, the force will be negative. Try to figure out why.

• Science World entry on momentum conservation. For those unfamiliar with calculus, read all of those d's as deltas. When the change in momentum is not zero, we have the other side equal to J, the momentum.

What did we learn!?

Distributions:

• Section 5001
• Section 5007
• Section 4990

• The centripetal force is "general force" like tension. It requires a source, like a string, or gravity, or... tension. Repetitve much?
• Circular motion can be paramterized by a couple of constants, most notably r and omega. See eqn 1.
• The Stopwatch program takes a running average. It needs at least 10 data points. You're shooting for the standard deviation to be less than the value entered into the box for it to stop. If the calculated value begins to diverge from the entered value, you need to adjust your speed.

• If the pink disc looks like its "rotating" within the hole, that means your device isn't level, try to relevel it.
• Remember that you have two equations to look at and that at any given time, you've got two parameters that are the same, and one that varies.
• One thing I can guarantee you is that the period cannot possible depend on one of the factors in the other equations. Figure out which one that is before you come into the lab.
• This lab is simple, but it's also somewhat deceptive. Know your concepts, and the technique will come to you quickly, and you'll get out fast.

• Circular coordinate system - Check out this to get a feel how we make things easier on ourselves when it come to rotation.
• Circular Motion with Weight - This is similar to what we're doing, but in our case, the weight will be out of the plane of the screen. The tension will be equivalent, however.

What did we learn!?

Distributions:

• Section 5001
• Section 5007
• Section 4990

Because I know you guys aren't reading these anymore, I'll simply post the averages and such here:

• Section 4990 - 21 +/- 1.9
• Section 5001 - 22 +/- 1.7
• Section 5007 - 22 +/- 1.6

Because I know you guys aren't reading these anymore, I'll simply post the averages and such here:

• Section 4990 - 21 +/- 2.5
• Section 5001 - 21 +/- 2.4
• Section 5007 - 22 +/- 1.9

Because I know you guys aren't reading these anymore, I'll simply post the averages and such here:

• Section 4990 - 20.8 +/- 2.38
• Section 5001 - 22.6 +/- 2.04
• Section 5007 - 21.7 +/- 2.11

Because I know you guys aren't reading these anymore, I'll simply post the averages and such here:

• Section 4990 - 22.9 +/- 1.05
• Section 5001 - 23.2 +/- 1.4
• Section 5007 - 22.6 +/- 1.61