# Week 1 (Aug. 14 - 16)

Welcome to General College Physics at Wisconsin Lutheran High School! The sidebar (to the right) has some basic information about this course, such as the Professor's contact information and the textbook we will be using. You might wish to take a look at that first.

Reading: PSE Chap 1, Physics and Measurement
In the first week, we'll begin by talking about Physics and Measurement. You should read chapter 1 of the textbook: the Pocket guide to accompany Physics for Scientists and Engineers (PSE) for this week.

Topics: I'll be covering some preliminary information on units such as length, time and mass. We'll discuss unit conversions and learn the valuable technique of dimensional analysis

Lab: To put this into practice, we'll do an experiment on pendulum motion during week 2.

Homework Problems for this week: Here are some problems involving the concepts of dimensional analysis, significant figures, and estimation. You may work on these with a friend, but you must write up and submit your own solutions. To receive full credit, your solutions must be handed in to me by noon on Thursday of Week 2. I do not plan to grade your solutions; I will just give you credit for handing in your best attempt. These problems serve as practice to prepare you for quizzes and tests.

1. Coulomb's law allows one to calculate the force that one electrical charge exerts a second, nearby, electrical charge. The formula for Coulomb's law is: (Force) = (coulomb's constant) * (charge 1) * (charge 2) / (distance between charges)^2. Don't worry if you are not familiar with this formula. Just use the technique of dimensional analysis, to determine the dimension of coulomb's constant. What might be the units of coulomb's constant? Answer: The units of the coulomb constant in SI are Newton-meter^2/coulomb^2. The dimension is M L^3 / T^2 Q^2
2. The speed of a wave traveling on the surface of the ocean depends only on (i) its wavelength and (ii) the acceleration of gravity. Using the technique of dimensional analysis, find a mathematical formula for the speed of the wave. Answer: v is proportional to sqrt(g * lambda).
3. Calculate the density (in grams per cubic centimeter) of a solid cube that measures 5.00 cm on each side and has a mass of 351 grams. Pay careful attention to significant figures. How many are there in your answer? Answer: Density = 351 grams/125 cc = 2.81 g/cc.
4. Approximately how many ping pong balls can be placed (in a single layer) on the surface of Lake Michigan? Do not look anything up anywhere. What quantities do you need to estimate? What assumptions must you make? Remember, when estimating, use only one significant figure. Answer: I'll estimate that the length is about 300 miles and the width is about 70 miles. Maybe 500 km long by 100 km wide. That's 50,000 km^2. A ping pong ball has a radius of about 2 cm. So its area is about 10 cm^2. So about 5 x 10^13 balls will fit.

Quiz: not yet (it's the first week!)

Classroom problems: As a reminder, these are some of the problems we worked out in class…
1. Dimensions and units: the universal gravitational constant, G, that appears in Newtons' universal law of gravitation.
2. Dimensions and units: energy, E, that appears in Einstein's formula E=mc^2.

General College Physics