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17 February 2009

Know your fundamentals

Pitchers and catchers have reported to spring training. Woo-hoo! Spring is just around the corner, as is spring break here at Woodberry. My family will be heading to Jupiter, Florida, where the St. Louis Cardinals hold their camp. The Nachoboy, my almost-six-year-old, has decided that he is a Cardinals fan, mainly because he could recognize the bird on their uniform since he was about two.

What will the Cardinals be doing in Jupiter, and what relevance does that have to a physics blog?

The Cardinals will be drilling their fundamentals – pitchers covering first base, ground balls to the infield, cutoff throws from the outfield, and so on. You know, the same things that the middle school baseball team works on at practice. Sure, the Cardinals are professionals, and are some of the best ballplayers in the world. Yet, they still work hard on their fundamentals.*

Advanced physics students may not think they need to drill physics fundamentals, but they often do. Simple recall of equations, units, and definitions can lead to stronger test scores. Drill must be handled carefully, though. On one hand, advanced students will turn off instantly if they feel they are being made to do “busy work.” On the other, less-than-advanced students must not be made to think that success in memorizing formulas is equivalent to success in truly learning physics.

The balance I have struck is never to include recall-style questions on homework assignments, but to give regular “fundamentals quizzes” in class. These recall quizzes are weighted heavily in the students’ grades; I also give rewards such as pieces of candy or exemption from future work to those who do well on fundamentals quizzes.

Since my AP class is preparing for their trimester exam next week, I thought it a good time to hit the fundamentals quizzes hard. The 45-minute lab portion of today’s class was devoted to fundamentals. I had four 10-question quizzes prepared. Everyone took the first quiz; the students traded and graded. (I certainly did not provide a key… they had to look up and/or argue about anything they weren’t sure of.) Anyone who got 9/10 or better could leave.** Everyone else got to take the second quiz, and so on and so forth.

As it turned out, 4 of 15 students got to leave early. Everyone else got the benefit of taking four different fundamentals quizzes. I have no doubt that these folks are much better prepared now for next week’s exam.

Below is a typical fundamentals quiz, for which I allot 5-7 minutes. In a future post I’ll make some suggestions about how to write your own fundamentals quiz.

* And, some would say professional ballplayers should work even harder on fundamentals, especially if they’ve ever watched the Cincinnati Reds defense.

** Leaving early from lab is a major perk, one that has not yet been extended to anyone in the class this year.

1. Two masses are connected by a string over a pulley. How many free body diagrams do you make?

2. A car smashes into a tree. The driver of the car is not held in place by a seat belt or any other restraining device. Just after impact but before the driver hits any part of the car:
(a) How do you know the driver’s velocity?

(b) How do you know the driver’s acceleration?

3. A block of mass m slides down an incline of angle θ . What is the component of the block’s weight parallel to the incline?

4. Write the ideal gas law. What are the standard units that should be plugged in for the P term?

5. Which of the following quantities is always conserved in a collision? Circle all that apply.

kinetic energy

(a) Where is the velocity of an oscillating mass on a spring largest? Circle one.

At the equilibrium point
at the maximum displacement
(neither of these)

(b) Where is the acceleration of an oscillating mass on a spring largest? Circle one.

At the equilibrium point
at the maximum displacement
(neither of these)

7. A wire carries a current I to the left. What is the direction of the magnetic field at point P?



8. What is the equation for the magnitude of the magnetic field produced by a wire?

9. What is the equation for the magnitude of the magnetic force on a wire?

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