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[Phys-L] FCI objectives



Good Morning,

I am planning on giving the FCI next year at the beginning of the year and at the end of first semester. (I am still an FCI skeptic on many levels, but no matter for now...) I have some questions:

1. I believe in giving my students a clear statement of what I am going to test them on at the end of a unit. So I looked on-line for a summary of the objectives that the FCI tests. I didn't find one. Hs anyone seen such a thing?

2. I wrote up a summary of what I believe the FCI tests. It seems like it's a pretty short list. I would like to give this list to my students after they take the FCI for the first time and then use it as the basis for class discussions and explorations. I'll paste the list below. Does anyone feel that it is too close to the test? I know that Mazur dismisses concerns about teaching to the test - "We tried that. It doesn't work." But still, I am trying to be clear about the content without giving away any specific question.

3. Am I missing anything?

My next step is to develop specific Interactive Physics simulations to target each of these areas. I will share them on my website as they are ready. This leads to my next question:

4. Suppose I want to measure whether my simulations are helping. I suppose I could use the simulations in one of my sections and not the other. But how do people actually go about doing this? My students talk to each other. Do I come up with a placebo-like activity to fill the time that the other class spends doing simulations? Seems unfair to that group...

Anyway, here' s my summary so far, in no particular order. Each of these 8 paragraphs will be paired with a simulation.

I welcome any comments or suggestions.


Near the earth' surface, if we can neglect air friction then objects all fall with the same gravitational acceleration. That acceleration is nearly constant as the object falls. The more massive object WEIGHS more, but it is also harder to accelerate - due to its greater mass. These two effects "cancel" each other out, resulting in the accelerations being the same.

When no forces act on an object, it continues with whatever velocity it already has. So it if was at rest, it remains at rest and if it was moving, it remains in motion in a straight line at constant speed. There is NO FORCE required to keep this motion occurring. If you are thinking back to a point in the past when the object may once have been at rest, then you are right to suspect that a force was involved in ACCELERATING the object to get it in motion. But now that it IS in motion, no force is required to KEEP it in motion. Objects do not have a "memory" of when they were at rest or a preference to be at rest. But they also do not have a memory of when a force acted. They accelerate only while they experience an unbalanced force. If we remove the force, they then continue with the velocity that they have at that point.

In EVERY interaction between two objects, NO MATTER WHAT THE CIRCUMSTANCES ARE, when one object exerts a force on the other, the second object always also exerts a force back on the first object. These two forces are ALWAYS equal in size and ALWAYS in opposite directions. However, the resulting accelerations do NOT have to be equal for two reasons: 1. Each of the objects might have other forces acting on them, contributing to the acceleration. And 2. Even if there are no other forces involved, the accelerations these two equal and opposite forces produce also depends on the masses of the objects involved. The larger mass will experience a proportionally smaller acceleration.

An unbalanced force always accelerates an object. And if it is accelerating, its velocity must be changing. That could mean that it is speeding up, slowing down, OR CHANGING DIRECTION! If the force is in the same direction as the velocity, it makes the object speed up. If it is in the opposite direction, it makes the object slow down. And if the force is perpendicular to the velocity, it causes the object to follow a curved path. In that case, the direction of the force and the direction of the acceleration are both TOWARD THE CENTER of the circular path. And, as we have already noted, objects have no memory for forces. If you remove the force that was making the object curve, the object continues with whatever straight-line velocity it has at that moment when the force was removed.

When an object is observed to be at rest or moving at constant velocity, you can be sure that any forces that act on the object are "balanced". And this has to be true in each component direction: the horizontal forces have to balance and the vertical forces have to balance. For objects moving at constant velocity, once again, it is reasonable to suspect that if in the past they were at rest, there must once have been an unbalanced force which accelerated the object. But NOW that it is moving at constant speed, the forces must balance. On the other hand, if the applied forces do NOT balance, we can be certain that the object IS accelerating.

Quantities that have magnitude and direction are called vectors. Examples of vectors include force, velocity and momentum but not time, mass or energy. An important thing about vector quantities is that they do not always add the way non-vectors (scalars) do. You can add them the "regular" way if they are in the same direction. But if they are not, you have to add them in a way that takes into account the direction. One method is called the tip-to-tail diagram. In particular, if the vectors you are adding are perpendicular, the sum (or "resultant") is the hypotenuse of the right triangle formed with the vectors as the two legs.

Projectile motion consists of motion in two dimensions. It is easiest to understand as the combination of two independent perpendicular component motions: horizontally, the projectile moves at constant velocity (because there are no forces acting on it in the horizontal direction). And vertically, the object is in free-fall, experiencing the accelerated motion that the force of gravity causes. The combination of these two component motions causes the object to follow a parabolic path. You get that parabolic path any time an object moves at a constant velocity in one direction while experiencing a constant force in second direction, perpendicular to the first.

The average velocity of an object over any time interval can be found by dividing the distance traveled by the length of the time interval. If over a period of time, an object is traveling at a constant velocity along a straight line, you will calculate the same average velocity for any chosen interval during that time. And for successive equal time intervals, the object will travel the same distance. If that in fact is the case, we can conclude that the acceleration is zero. On the other hand, if during successive equal time intervals, we observe increasing distances traveled, then the object is accelerating.



And if you have still read this far, thank you for your time!

Phil