Apologia Physics: Centripetal force demonstration

Centripetal force is Newton's First Law in practice!  Newton's First states that an object in motion (or at rest) will stay in motion (or at rest) unless acted upon by another force.  In the instance of circular motion, centripetal force makes an object move in a circle rather than going straight.

One experiences centripetal force in many ways: turning a corner in your car, going upside down on that circular ride at the amusement park, and as shown in the lab below, keeping water in the cup as the cup is upside down.

To perform the demonstration below you will need a piece of stiff cardboard.  I considered using plywood but if a student hit someone in the head that would not be good.  Drill a hole in each corner of the cardboard.  Attach a piece of string (we used acrylic yarn, strong but cheap) about 2.5 feet in length to each corner and knot together the other ends.  Place two paper cups on the cardboard and fill each with a couple ounces of water.

Swing the apparatus back and forth a few times then swing in a circle a few times.  Try swinging faster and slower.  Stop and repeat the process after adding a few more ounces of water to each cup.  Repeat again after filling each cup.

Do this outside as some students will not swing fast enough and the water will come flying out on everyone within range!

Students should be able to feel the change in centripetal force, as the tension on the string, which will be greater with more weight and also greater with more speed.

Apologia Physics: Static Friction

Static friction is the force that holds two objects that are touching each other at rest.  Kinetic friction is the force between two objects that are touching each other but are in motion.  The coefficient of friction is a measurement of the amount of friction.  We can easily measure the coefficient of static friction.

We will place a plastic car with its wheels removed on a board.  Raise the board until the car begins to move.  Measure the height of the end of the board and use the pythagorean theorem to calculate the angle of the board in relation to the floor when the car begin to move.  Also use a protractor to measure the angle as a check on your calculations.  Calculate the coefficient of friction.

Perform the test again with a light weight in the car and again with the heavier weight in the car.  Perform all three tests again with different materials attached to the board.  We used wax paper, .aluminum foil, and two grades of sandpaper.

Rank the materials in order of their coefficients of friction.  The material with the lower coefficient is more slippery.  The sandpaper is abrasive.  It has a high coefficient of friction.

How do you calculate the friction?  The gravitational force that runs parallel to an inclined surface is equal to the weight of the object times the sine of the incline angle.  The gravitational force that runs perpendicular to the incline surface is equal to the weight of the object times the cosine of the incline angle.  The normal force of the board pushing up against the car offsets the force of the car pushing down on the board.  Therefore the frictional force that is offset when the car begins to move is equal to the coefficient of friction times weight times the cosine of the angle.  The force that keeps the car from sliding down the board is equal to the weight times the sine of the angle.  Since these forces are equal until the car begins to slide, the coefficient of friction times weight times cosine of the angle equals weight times sine of the angle.  The coefficient equals the weight times sine divided by weight times cosine.  The weight cancels out!  The coefficient of friction is equal to the sine divided by the cosine of the angle or more simply the tangent of the angle.  Putting weight in the car does not affect the coefficient of static friction.  None of this applies to the coefficient of kinetic friction that will be addressed in a future chapter of the book.

Another way to calculate the angle is to take the inverse sine of the height divided by the length of the board.  Use this calculation to check the angle measured by the protractor.

Apologia Physics: Torque and First Class Levers

Our class did a lab Torque and First-Class Levers from NSTA's Take Home Physics book. 

Rotational torque equals the product of weight and distance from the axis of rotation.  The lab above is an easy way to demonstrate this calculation.

Materials include a ruler with a hole in the middle, some string, washers, and paperclips.
Construct the apparatus as shown in the lab.  We found that the hole in the middle of the ruler was not exactly in the middle so we taped a small washer on the back of the ruler in a location that would balance the ruler.  The ruler should hang horizontally before you start!

Record the number of washers you hang on the left side of the ruler at the distance prescribed in the lab.  Balance the ruler by adding the number of washers on the right side of the ruler, as prescribed in the lab, then record the distance the washers needed to be from the axis to balance the ruler.

Multiply the number of washers times the distance from the axis.  The resulting number should be equal.  Calculate the margin of error.  The students had margins of error of ten percent or less.

Apologia Physics: Module 7 Measuring Tension

The object of this demonstration is to determine the tension on two strings on which hangs a weight.
The students obtained a weight from a balance scale.  They measured the weight to be 147.5 grams.  They hung weight from a spring scale determine its accuracy. 
Next they hung the weight from two springs as shown below.  First they hung the weight so that it was in between the two scales such that the angle of the scale and string to the base board is equal on both sides.  Then they hung the weight such that it was to the left of center.  The angle of the scales and string to the base board were therefore not equal.
Using the equations from Example 7.2 in the book, they will calculate the tension on the string in each situation for both sides and compare to the reading they took on the spring scales.

Statistics: Sampling with and without replacement

How do they count the number of deer in a wooded area?  Can they round up all the deer in the woods and count them?  If so, how would you know you had all the deer?  Scientists do a catch, mark, and release process.

We simulated this process by counting white beans.  Each student was given a cup about 2/3 full.  Each student had between 400 and 500 beans.  Pull 15 beans and mark them with a marker. Return the marked beans to the cup and mix well.  Pull a sample of 10 to 25 beans and record the total number of beans in your sample and the number marked.  Return the sample to the cup and mix well.  Repeat this process ten times.  This is called sampling with replacement.  

Add the number of beans in the samples and the number marked.  Set up a ratio to estimate the number of beans in the total population and then record the percent error.

Repeat the process but do not return the samples to the total population.  Perform the same calculations.

Which method was more accurate?  What could be done to make the process more accurate?

Mark and Recapture Lab

Apologia Physics: Module 6: Friction and Inertia

Friction Lab

We are studying friction.  To move an object requires a force.  This force is equal to the friction coefficient (Greek letter mu) times the Normal Force (mass times gravity expressed in Newtons).  To demonstrate the friction coefficient of different materials we placed an object on a wooden ramp and raised the ramp until the object started to slide.  We then recorded the angle of the board.  We repeated the same exercise with different materials taped to the board including: aluminum foil, parchment paper, light or fine grade sandpaper (high grit number) and rough or heavy grade sandpaper (low grit number).  Interesting fact: the grading of sandpaper is based on the number of holes per square inch in the screen used when sieving the grains of of grit during sandpaper manufacture.  Thus fewer holes are bigger holes which allow larger grains to pass through.

Results: aluminum foil is smoother than wood, parchment paper smoother than foil.  Large grit is rougher than small grit sandpaper and both had a higher coefficient of friction than the wood.

To calculate the static coefficient of friction, find the formula in module 7. 
The coefficient of static friction is the tangent of the angle.  This is not true for the coefficient of kinetic friction!  Why is the mass or weight (mass times gravity) not used in this calculation?
The mass determines how much force is pushing the object down the slope.  The mass also determines how much the object is pushing down on the board.  The additional force pushing the object down the slope is offset by the additional static friction.

Apologia Physics: Projectiles with Vernier's Video Physics App

Last Thursday we made catapults from popsicle sticks and rubber bands.  We launched a ping pong ball and video recorded the projectile's path.  Today we used Vernier's Video Physics, see below for link, to draw a graph of the trajectory including time of flight and the distance traveled in both the vertical and horizontal directions.  The students picked six points from the graph and entered the x and y coordinates into their TI83/84 calculators.  We now have the quadratic equation for the line of the trajectory.  The students' assignment for next week is to use the formulas in module five of the physics book to determine the initial velocity of the ping pong ball and also the angle of flight.








Vernier's Video Physics app

Graph Image 1
Graph Image 2
Graph Image 3

Apologia Physics: Catapults or Projectile Motion Module 5

Module 5 topic is projectile motion.  Today we built a trebuchet and a catapult.  We fired a projectile, a ping pong ball, from the catapult and recorded the motion with Verneer's video app.  During the next class we will analyze the videos, graph the projectile movement, and separate the forces that act upon the ping pong ball, horizontal and vertical.  The paper trebuchet worked but did not send a projectile, a paper clip, more than a foot at best so we will not use that data but what we built will serve as a good model.

These are the links to the project descriptions:

Paper Trebuchet  and Craft Stick Catapult

Statistics: Graphing Absolute Zero

The Stats class used Flinn's Charles' Law Lab instructions today.  I wanted a real life example of collecting data and using the data to extrapolate.  We measured the volume of air (gas) in a syringe at different temperatures.  Basically, the syringes are in yogurt containers filled with ice water, boiling water, and room temperature water.  I had the kids mix the hot water with cold to get at least four or five data points.  We used 10 mL and 30 mL plastic, oral syringes with caps.

We found that the 30 mL syringes didn't work.  I insisted I needed 30 mL syringes--not just 10 mL syringes.  Guess what?  The 10 mL syringes worked better.  The results were surprising.


Here is one student's, Anna's, data:
Temp  (C)   Vol (change in volume mL)
19.5              5.5
13.3              5.0
9.4                5.5
63.8               7.0
30.6              6.25


Next the kids plotted, calculated, and graphed the linear regression with their TI 83/84 calculators.  Then, the kids went to the Window in the calc and extended the range: Xmin -300, Xmax 100, Ymin 0, Ymax 10.

Lastly the kids extrapolated to see the temperature at 0 volume.  Anna's 0 volume y-intercept was -360C.  Absolute zero is -273.15.  Her percent error is 32%.  Not bad at all!  We had a couple students with less than five percent error.  That was excellent and unexpected.  Remember we used syringes in yogurt cups for the water bath.

The lab coincides with Chapter 4 in Stats.  How do you collect, organize, graph, and present your data?

I'll post a lab report when the kids finish.

Statistics:Chapter 3: Part 2

The kids are working on worksheets from Chapter 3 activities from Mrs. Daniel's Stats blog.  I spent my class time explaining linear regressions and the LSRL, the least squares regression line. 

Apologia Physics: Module 4

Today, the kids did on your own problems for Module 4.  They are working on the test questions for Tuesday.  Tommy is having trouble drawing the vector.  We'll work on this skill.

Statistics: Chapter 3 Correlations

The kids worked on TI84 graphing exercises on p.186 and p.219 before class began.  (They're doing the same exercises again as homework to ensure the kids can do the exercise.)  (The variables are located in Vars Statistics or Y-Vars Functions.)  We went over half the slides in Mrs. Daniel's powerpoint 3.1--just before the formula to calculate r, correlation coefficient.  The kids can enter data in the stat function of the graphing calculator, calculate linreg, and graph linreg.  We reviewed those skills last time.  Be sure to practice entering data and graphing. 

Apologia Physics

Today the class worked on Vectors: The Vector Voyage and Walking Vectors activities.  The Walking Vectors should have been done outside, rather than in the basement. The kids ran into walls.  The point was you can shuffle the order of the vectors and still end up in the same spot.  I made five or six cards.  The kids did the activity, shuffled the cards and repeated it.  The walking did not work because, the kids ran into obstacles, such as walls and tables.  We drew the instructions from the cards on to graph paper.  That worked.

We did not begin the Vector Voyage; the kids are completing it for homework.

Statistics: Chapter 2 and Linear Regression

At the beginning of class, the kids did example 3.9 (p.200 textbook) Does Fidgeting keep you slim?  The class entered the data into L1 and L2, graphed the data, calculated the linear regression and displayed the regression with the data.  The kids learned how to turn on Diagnostic or r coefficient.

Do linear regression models frequently or the kids will forget how to enter, graph, calculate, and display linear regressions. 

We reviewed the Mrs. Daniel's WS 2.2  The homework for Tuesday is the Chapter 2 test.  Yes, the worksheet took most of the class period.

Statistics: Two new videos for the Normal Curve

One of the students took two hours to create two videos with instructions for graphing a normal curve and shading under the curve with a TI 84.  Take a look!

Statistics: Normal Curve

Update: There are two new videos with explanations how to graph the normal curve and shade under the curve here.

The first thing we did in class was graph normalpdf, normalcdf, and shadenorm with the graphing calculator.  The point was to understand how to shade different areas under the normal curve by setting upper bound, lower bound, mean, and standard deviation with these exercises or examples.    These examples have the screen shots.  This powerpoint has good instructions.

We spent about 30 minutes explaining that normalpdf (x) must be defined under y=, 1E99 or -1E99 represent infinity on the TI84, normalpdf graphing a standard curve or normal curve, shadenorm uses lower bound, upper bound, mean, and SD, and normal cdf converts a z score into a percentage.  Largely, we set the window and practiced shading.  We only spent a few minutes converting z score to a percentage or percentile.  The point was to learn how to enter the data.  The screen shots provide the answers.

For the remainder of the class, the laptop died.  We talked about a normal curve, defined z score, introduced the z score equation, talked about comparing scores with the SAT and ACT as an example of standardizing two scores with different scales.  Their homework is to complete the overview and summary and the 2.1 worksheet for Friday.


We have a back-up Thinkpad for the seemingly dead laptop up and running.  Fingers crossed it works on Friday.  I am wed to the powerpoint slideshows.

Statistics: Graphing under the normal curve

The class is trying to integrate graphing calculators.  One skill is graphing under a normal curve.  The first step is to draw a normal distribution curve on the graphing calculator..  The link above has the screen shots for each calculation.  Shadenorm shades the specified area.  The TI84 sequence is Shadenorm(lower bound, upper bound, mean, and SD).  The mean for a normal curve is 0 and the standard deviation SD is 1.  To shade the entire normal curve the sequence is Shadenorm(-1E99, 1E99, 1,0) or (-4,4,0,1)  -1E99 or 1-99 represents infinity or is the program on the TI84 for infinity.  I defined the area under a normal curve as having four SDs in either direction from the mean 0.  Left is designated with - and right is +.  These exercises for shading the area under the normal curve and using normcdf to calculate percentage  were very helpful

It took hours and hours to find useful information about how to graph the normal curve and shade under the normal curve.  The exercises are very useful because they have picture!  The information to the right of these screen shots of the shading are normcdf( and calculate percentages.  In order to shade areas under a normal curve you must have the normal curve defined in y=, the window set for X and Y,  before shading.  Once you have y= and the window settings, the sequence is shadenorm(lower bound, upper bound, mean, SD), such as shadenorm(-1E99, -1.67, 0, 1)  Remember to add the boundaries AND the mean (0 for the normal curve) and SD (1 for the normal curve).  The other step I forgot initially was ENTER.  I defined shadenorm( 1.67, 1E99, 0,1) and forgot to hit ENTER.  I kept entering GRAPH. 

Statistics:chapter two Describing Location in a Distribution

We started class by reviewing the Hamburger and Hank Aaron Home Run activities.  We calculated a five point distribution for each (min, max, Q1, mean, Q3) and also the IQR.

Began chapter two by reviewing 2.1 Overview.

Apologia Physics

Today we reviewed the test questions for Module 2.  Everyone got number 7 wrong.  The question asked was to calculate when two vehicles would collide head on if they were driving toward each other.  The key to solving the problem is to add their speeds together before calculating the time to travel the distance.  One student calculated the time for each vehicle to cover the compete distance between the two vehicles.  That did not take into consideration that the vehicles would collide before reaching the end the distance between them.  I assigned another problem from module 2 for the next class so we get more practice with this type of problem.

Apologia Physics: Module 2 Motion

The first thing we did today was to review definitions of speed, velocity, and acceleration with the calculations and shapes of the motion graphs.  The kids were assigned On Your Own problems from the book to do at home.  They bring these back completed; we spend time in class reviewing the problems that posed difficulties.  I made copies of the Chapter 2 test and distributed them.  Friday, we'll check the tests in class.  This is the basic class format: labs, exercises, On Your Own problems, and a test.

Statistics: Graphing and Histograms

Today, Deb led the Stats class.  She reviewed linear regressions and one variable stats  she introduced normal distribution graph, how to shade, and how to clear shading.  Then, she used this data for Utah and Florida--located in this packet to show the class how to create population pyramids as good examples of histograms.   BTW, population pyramids are key topics in Human Geography and AP Environmental Science.  The class discussed the implications.  For example, there will be more demand for infant diapers in Utah and adult diapers in Florida.  The point is to differentiate between a bar chart of M&M candy colors and a population pyramid double histogram.  One can draw a number of inferences regarding future growth, its shape, etc.  Below is an example from one of the kids.

Statistics: A little Graphing Calculator and Chapter 1

The kids have been working with the graphing calculator doing different exercises at the beginning of class.  The first week, the kids met with the Chemistry class to learn how to use the graphing calculator to model data. 

This week, my wife, Deb, reviewed histograms, box plots, and calcs the first five or ten minutes with the Statistics class.  One student, Angel, had a question about entering and calculating two variable statistics on the graphing calculator.  Deb showed the class how to specify which data and how the calculations are displayed on the calculator.

I'm following Mrs. Daniel's AP Stats Blog. The textbook is difficult to read as there are many terms, formulas, example calculations to be done.  I thought this was boring and it was difficult for me to determine what was important and reduce to a few pages of notes.  However, Mrs. Daniels, a teacher of AP Stats, has a blog which contains for each chapter: summary of terms, notes to present each major section of each chapter, activities for the students to complete, and a reference sheet to hand out which includes important terms, examples of graphs, and formulas.  I plan to present to the class Mrs. Daniel's presentation, have the students complete a couple of hands on activities, have them complete at home the overview questions.

Today, Friday Sept 19, we reviewed the chapter one overview which they had completed at home.  We reviewed the drive time calculation exercise including mean, median, and standard deviation for the students' commute time to class.  This is one exercise where we will calculate the standard deviation by hand and then in the graphing calculator.  I explained the difference between the standard deviation s (std dev for a sample) and omega (std dev for the entire population).  In the first calculation divide by (n-1) rather than n (where n is the number of data points) because of Beeson's correction.  Since we are typically using a sample, not the entire population, of data, the standard deviation is probably understated square of each variance from mean, then dividing by n-1 before taking the square root.

Statistics: Standard Deviation

Once Stats completes the M&Ms and Water labs, Rob is teaching standard deviation (SD).  The TI84 calculates SD.  Rob thinks the kids should calculate it manually once to understand variance and just what SD is.  Khan Academy has step by step instructions.  Rob is using How long does it take you to drive home from school? to review mean, median, and mode, while teaching SD.

Once he finishes this activity, I would like to do the Parking Lot Biodiversity Lab.  A biodiversity index examines variance in ecosystems.  Another activity for the kids is constructing Population Pyramids or histograms.  These two activities show kids how the stat activities are relevant to Ecology and Human Geography.  This activity, Power of the Pyramids is excellent.  Read the questions.  When I use these exercises, we always discuss the implications of countries such as Japan or in Western Europe with low fertility rates AND countries with high fertility rates.  My focus is on economic  implications, not birth control or ZPG.

This census population exercise comparing states and even cities is excellent.

Statistics: Intro to Graphing Calculator

Update!  Yes, we finished the M&M lab, graphed the data in a histogram and practiced several data sets!   Whooooo!  This seldom happens!  We finished the planned lessons.


The Chemistry class meets Tuesdays and Fridays this year.  Tomorrow, my husband, Rob, and I are doing another combined Chemistry and Statistics class to introduce experimental design and how to use the graphing calculator.  

First, we're using this graphing exercise to see if the kids can enter the data into the STAT function, turn on STAT PLOT, set the range, graph the data (depth and average temperature), calculate the linear regression, and overlay the line of best fit over the scatter plot data.  In other words, see if they remember our lesson from Tuesday.  Maybe.

Next, Rob and I are going to do this Statistics and Probability Lab with M&Ms.  He and I have 15 small cups of 50 gram samples of the candies, from a party-size bag of regular M&Ms.  Most of the M&M labs use individual bags of candies for each student.  The party-size bag was cheaper; so we weighed 50 g. samples before class.  

We decided to have a quick discussion about experimental design, hypothesis, and controlled variables before the lab.  Basically, the kids are going to predict which color M&M candy is the greatest percent in the candy sample (alternate hypothesis) or the percentages of each color are the same (null hypothesis).  This article explains how two companies produce M&Ms varies slightly by company. The percentages by color are in this article--for milk chocolate candies!  

We are going to give each child a cup with 50 grams of candies.  They will count the number of each color candy and calculate the percentage of each color in the cup.  Next each table of three kids will pool the data.  Finally, we'll pool and calculate the class data.  Next Tuesday, Rob is going to do two other exercises with the Statistics class, such as sampling with replacement and outliers.  Once we have the class data, the kids are going to graph it in the graphing calculators and produce histograms--bar graphs by color.  Yeah!  

What does this have to do with Chemistry?  Very little.  However, it will allow a brief discussion of experimental design and introduce the kids to the graphing calculator.

Statistics: From the beginning

At the beginning of class, Rob and I switched.  He monitored Chemistry and I taught Statistics how to create a stem plot or a box plot.  We entered data (2,4,6,8,10,12) into L1 of Stats, graphed the stem plot, calculated one variable (1 Var) statistics and used the TRACE function on the stem plot or box plot to locate the quartiles and median.  We repeated with new data (5,10,15, 20, 25, 30).  The short-cut to set the Window or Range is Zoom 9 for STAT functions.

We reviewed definitions for mean, median, mode, quartile, a five point summary, box plot, examples.  They drew a bar chart or histogram based on the data in the book.

Apologia Physics: Motion

The kids are working on several motion labs: Ramps and Balls, Go Pro with Hot Wheels Car, and Are You Speeding?  The introduction to Motion allows for experimentation.  Are You Speeding? uses Pasco Spark with the motion sensor.  The kids literally follow the Sparkvue lesson to learn how to collect motion data with a motion sensor.
On Tuesday, the kids did experiments with ramps and balls.  (The ramps are 4x6 boards cut into one meter lengths at Lowes.  The ball is a Pinkie ball.)  The object was to demonstrate average speed and acceleration.  They leaned one board against a book shelf.  The other board was placed on the floor at the base of the first board.  How could they measure the acceleration of the ball as it rolled down the ramp?  We do not have a radar gun to measure the instantaneous speed at the bottom of the ramp.  We approximated the top speed of the ball by measuring the time it took to cross the one meter board on the floor; the assumption being that the ball would not slow down significantly on the flat portion.  After we measured the elapsed time of the ball on the one meter board on the floor, we compared that to the starting speed, which in this case was zero, got the difference and divided by the time elapsed by the ball rolling down the ramp.   This was the acceleration experienced by the ball on the ramp.  It is crucial that the students calculate the acceleration by dividing the change in speed by the time and include all units of measure.  Acceleration is changed in speed divided by time.  Therefore if they set up the calculation correctly the resulting measure is meters per second squared.



The kids used Hot Wheels track with the Go Pro Hero and the Hot Wheels car to measure the same as above.  By observing the GoPro video, we could determine the speed by counting the frames of video recorded by the car covering the measured meter.  It helps to put some colored tape on the beginning and end of the measured meter of Hot Wheels track so one can see the beginning and end of the measured distance.  After counting the frames, one must look up the frames per second for the GoPro and convert frames to seconds.  We were not able to use the motion sensor to determine instantaneous speed but they had fun trying it.

We used the motions sensor to measure a student's walking back and forth.  This measures the displacement from the beginning point.

The assignment for Tuesday is to read all or module 2 and complete the on-your-own problems.

Apologia Physics: What did we do today?

Today, the class reviewed terms; we spent most of the class reviewing the 'on your own' questions and answers.  The kids are completing the first test at home.  Tuesday, I'll go over any questions.  We should be ready for Motion.  I have several fun labs.

Apologia Physics: Week One and Two

Friday, Week Two, the kids are going over their homework, the 'On your own' questions and taking a test for Module 1.

Here is an outline of the activities for Day One.  First, we did this physics math pretest.  It took all class period taking the test and reviewing the answers.  This is important information; one of the kids did not know how to convert units.  Next, the class did the Accuracy and Precision Lab and finally Bowling for Density.

This other density lab we did is It's all about Density from Flinn Scientific.  The kids determine if which method, volume by displacement or volume by geometry is more accurate.  The class can determine which method is more accurate by determining the density of a variety of objects and comparing the densities they derive with know values.  My wife and I both use this lab for Chemistry and Physics.  We use density blocks and have a set of mini cubes like these.  We use household objects: toy block, marbles, small balls, cylinders, etc.  The kids must use a variety of objects for the lab.  Some of the objects will not fit into the graduated cylinder---deliberately!  This is an opportunity to introduce percent error to the class.  Below are photos of the equipment.

Apologia Physics: Special Topics reports, how did they go?

In April I assigned various special topics for the students to investigate and report back to the class.  These topics were assigned for various reasons: to become familiar with current technology, to improve writing skills, and to practice presentation skills.  This needs to be done in more classes as it appears that many of the students lack these skills!

Now on to the subjects:

How do high and low temperatures impact the range of an EV (electric vehicle)?   Fortunately there is some research published on this topic.  As EV's become more popular potential owners need to be aware of the impact of temperature on the power of a battery, and more importantly, the impact of running the heater or air conditioner.  Depending on the range of temperature and the creature comforts in use, range could decrease 10 to 20 percent!

In their comparisons to a gasoline powered car, it was evident that many students had no idea how various components of the car worked.  For example, one student claimed that running the heater would also reduce efficiency but in reality heat in the passenger compartment is created by using waste heat otherwise cooled by the radiator.  My Dad showed me how many systems in the car worked, but it was easier when you could see and access the radiator, battery, spark plugs, etc.  He also used this education as a way to sign up my brother and me for free labor changing tires, washing and waxing, oil changes etc.!

Operating cost comparison for an electric, gas, and hybrid car.  Since these students are home-schooled and typically from large families, there is more of a practical attitude and less political correctness when it comes to the economics of electric and hybrid cars.  The gas powered car was significantly less expensive to operate owing to the lower purchase price, which also resulted in lower costs for financing, insurance, and property taxes.  In terms of an economic break even point, they discovered that it would take at least 8 to 10 years for the EV to be cost effective; and that only works if you do not have to replace the battery!  Or in the case of many Teslas, replace the door handles which cost a grand a piece.  Also, as a finance guy professionally, I do not invest where there is an expected 8 or 10 year payback!

What is an Eddy Current?  An Eddy Current is easy to show.  Just drop a relatively strong magnet down a copper tube.  The magnet creates a magnetic field parallel to the tube.  These fields create a circular magnetic field above and below the magnet, perpendicular to the tube.  This charge on the bottom is the same as the charge on the bottom of the magnet.  These charges repel and make the magnet fall much more slowly than it would based on just the pull of gravity.  We did not find many practical uses for the Eddy Current but it was fun to discuss, demonstrate, and draw pictures of the fields.

How does a Mag Lev train work?  Another example of magnetic fields in use.  One has to draw a detailed diagram to fully understand where the magnetic fields are placed to make the train float above the "track"  Even more interesting is how a linear motor works.  By switching the magnet fields on the side of the tracks back and forth the magnets attract the train as the train approaches and repel the train as it goes away.  These fields can also be used to stop the train!   This is a very simplified explanation so go do your own research and look at some diagrams!

How do wireless chargers work?  I am not an early adaptor by any means so at this time it looks like wireless chargers are for people too lazy to plug in their phone or tablet to charge.  However when the wireless charging towers are further developed so that devices can be charged as a group meets around a conference table this would end the struggle to keep a couple dozen phones, tablets, and laptops charged during a long meeting (of which I have been in attendance for quite a few in my career in business).

Everyone had a good time presenting their topics and asking many questions of those who were presenting.  We are now on round three (at least) of revisions to their written reports.

Next year we are teaching Chemistry, Statistics, and Physical Science which will include participation in a science fair.  We will probably therefore offer a writing workshop at the beginning of the school year for all the students.  Our library has a good course online; we will probably use that as a base.

A tip for writing research essays

If you are assigned a research project, before you determine your topic, figure out the professor's field of expertise.  Then pick a topic as far from that specialty as you can.  The professor will be much less critical.  If you write about something on which he or she is very knowledgeable, you will get torn up!

Other practical tips based on what we are seeing from our students:

Don't use contractions
Proofread before you finish
Font style should be something standard and size should be 10 or 12
Paper should have an introduction and a conclusion
Introduction can list the topics to be covered
Then have a paragraph that discusses these topics in the same order
Know the difference:  it's and its, there and their, etc.  Use Spellcheck but it will not correct for incorrect use of these words
When you paraphrase make sure it sounds like your own voice not that of the writer
Cite your sources.  In some of our topics, the age of the source is critical as technology changes so quickly.

Apologia Physics: Electrical Circuits (and demonstrating with Snap Circuits)

Students need to be familiar with various terms and calculations that relate to electrical circuits. They should be able to define VOLT, AMP, conductor, switch, resistor, capacitor, fuse, circuit breaker, series and parallel circuits. They should be able to explain how a battery stores and releases energy.

Electrical circuit: manages the flow of electrons by shaping the conductor (often copper wire) and controlling the electrical field.
Volts: electrical potential
Lead acid batteries, common in cars, use an Oxidation/Reduction reacting to create electrical current.  LEO the lion says GER.  Loss if Electrons Oxidation, Gain of Electrons Reduction.
Resistance: how a conductor impedes the flow of electrons.  Electrical heating devices use resistance in wires to create heat.  For example, toaster, coffee maker, electric stove.  There is resistance in all electric lines.
If resistors are in series the total resistance is the sum of the resistance in the resistors.
If the resistors are in parallel, the total resistance is 1/Rt=1/R1 + 1/R2  Therefore if two resisters (10 ohms ad 20 ohms) are in series the total resistance is 30 ohms.  If they are in parallel, the total is 6.7 ohms.  Go ahead and prove the math!


We demonstrated much of this with Snap Circuits.  Each student was instructed to put together a number of circuits which used a switch, resistor ( and demonstrate to me the resistor worked ), rheostat ( a variable resistor ), sound device, light bulb, fan, etc.  Also put together circuits which demonstrated how a series and parallel circuit worked.  Each demonstration was then supported by a drawing in which the students had to use the correct symbol for the various electrical devices.

We discussed personal situations which demonstrated how fuses and circuit breakers worked in their houses.  Older houses very often do not have enough power in their wiring that you can run your coffee machine and your toaster at the same time in the same  room.  You have to find an outlet on a different circuit to run the toaster if you have already started your coffee pot!  Do not under any circumstances replace a fuse with a penny so that you can get more power to an appliance; good way to start a fire.    There are various levels of power (amperage) in various circuits running in your house.  Obviously it takes more power to run your kitchen than your bedroom.  It takes more power to run your washing machine or your HVAC than your television, etc.

Apologia Physics: Electrostatics

Electrostatics measure the instantaneous charge between two atoms.  For examples see the pictures below.  We rubbed balloons on our sweaters and on our hair to create static electricity.  It is best to do this on a cold dry day so you may have to change the order of topics in your Physics instruction to get this demonstration done before Spring.  Then we hung tape and yarn from rulers which extended beyond the edge of the table.  The static electricity attracted the tape and yarn.  We also applied tape to the table and ripped the tape off and hung it from a ruler.  Repeat with another similar piece of tape and hang it close to the other one.  They should repel because they have the same charge.

How is this static electricity created?  You actually rip electrons off your hair or sweater when you rub with the balloon.  Therefore the balloon takes on a negative charge.  The tape rips electrons off the table and therefore the tape takes on a negative charge.

An atom has protons and neutrons in the nucleus.  Electrons orbit the nucleus.  To change the charge of an object you add or subtract electrons as we did above.  The number of protons and neutrons does not change.

Apologia Physics: Current Topics for the study of Electricity

I struggle with anything concerning electricity and magnetism in my teaching of high school Physics.  Maybe it is because most of the other topics in Physics I relate to the operation of a car!  So I decided to veer away from the topics covered in our textbook and have the students do a small research project on topics that are relevant to current events.  These projects would also serve to update my knowledge.

The topics below came from several sources.  My wife and I helped judge a science fair for grades 6-8 at a local school in February.  Several ideas came from projects done by those students.  My students are also very interested in electric cars and of course all their electronic gadgets.  I have eight students and we came up with eight topics.  I have asked them to do some research, summarize their research into a one page paper including sources, present their findings to the class and lead a discussion of the topic with the class.  Here are the topics.

How do very high and low temperatures impact the range of an electric car?  How and why?  Explain change in chemical and physical reactions.

What factors impact battery life in an electric car?

Compare operating costs over several years for three similarly sized cars: gas powered, electric powered and gas/electric hybrid.

What is an EDDY current?  How is it created?  What are its uses?  Make a model.

How does a MAG LEV train work?  Where are they in use?

How does a wireless charger work?  Contact vs. Non-contact.  See article by Joanna Stern in the Wall Street Journal May 5.

Compare various aspects of performance of a gasoline powered car vs. an electric car.  Find comparable cars and/or cars in the same price range.

Compare the safety of a gas powered car vs. an electric car.

Projects are due after the Easter break.  I will follow up at that time.

On Thursday April 11 I sent the students a summary of how to write a five paragraph essay.  It is important to have an Introduction (containing your subject, hypothesis, scope, three main ideas), three paragraphs each discussing one of the main ideas, and a conclusion.  The conclusion needs to be based on what was discussed in the preceding paragraphs.

The verbal presentation to the class should be based on notes or an outline.  Do not read your essay and just refer to your notes if necessary.  No one wants to listen to someone reading a Powerpoint presentation!  I saw too much of this in my career in business.

Egg toss lab

We are studying impulse force.  Impulse is the force an object experiences when there is a change in momentum.  The change in momentum equals the impulse force times the change in time.  What time?  The time elapsed as the object changes momentum.

An easy way to demonstrate this is to toss an egg back and forth between two students.  How do you reduce the impulse force?  Look at the equation in the first paragraph. If a student tosses the egg to another student, the change in momentum is equal to the mass of the egg times the speed at which the other student throws the egg.  The catcher can either catch the egg with his hands fixed or he can swing his hands and arms back as he is catching the egg.

If you catch the egg and it stops very suddenly, it will probably crack.  This is great fun the first time!
If the catcher swings his hands and arms back as he catches the egg the egg usually does not crack.  The difference is much more evident if you catch the egg on a cookie sheet instead of your hands.  You can also use a bedsheet.

The key concept to understand is that the momentum is a constant in each situation so if you want to reduce the impulse force you must increase the time it takes to bring the egg from its initial speed to a stop.

There are several great examples in real life such as crush zones designed into the front of a car's frame and body, airbags in your car, etc.

The opposite is also true.  If you are hitting a baseball, you only have so much strength.  If you want the ball to have more momentum so that it goes further, you have to increase the time the bat is in contact with the ball as you are hitting it.  In many sports such as baseball, golf and basketball, this is called follow through.

Have fun with the lab.

class discipline

It seems as though some of the homeschool students I teach are not accustomed to deadlines and remembering to bring their completed work to class.  They also have a long list of excuses when they have not finished their work such a: the printer broke, they stayed late at sports practice, they were tired, etc.  They also insist on maintaining some practices that are not correct such as not using scientific  notation and forgetting to include units of measurement.

So we came to a mutual agreement.  Offending students would do pushups, just like in basic training for the military for each infraction.  Did not finish a report?  Ten pushups.   Present a problem solution and not express the answer in scientific notation?  Ten pushups.  The parents I have spoken to about this are all supportive.   The point I am trying to make is that when these students are in college, the military, or have a job,  none of these behaviors are acceptable!

The importance of being able to write well and appropriately to a scientific audience

The class has been writing their egg toss lab reports.  It is important that they write well but also write appropriately to a scientific audience.  In all writing it is important to use proper punctuation, grammar, and sentence structure.  It is also important to write succinctly and concisely and not use trite phrases.

I have never been able to write prose and poetry so I will not comment on the differences between what the students may have learned about writing in their literature, composition, and history classes and what I am teaching them about writing.  Hopefully those differences are not too great.

Examples of phrases and words I do not want to see in lab reports:  honestly, actually, grab the …, who would have thought?,  etc.

We also write lab reports in the third person, present tense, active voice, indicative mood.

For example:  The student rolls the ball.

Apologia Physics Module 9 Horsepower calculation lab

This module is about power.  Power is force exhibited over time.  Attached is a lab that will help you understand the stair climbing horsepower calculation.  Please complete the lab using these instructions and bring to class Tuesday.  Please make sure you have completed three trials that are reasonably similar in time.  If you have results that say you only have a quarter horsepower or that you have three horsepower try again!

Here is the horsepower lab with stairs.  This lab has calculations.