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August 2017

R2 Physics 02 – Velocity

For the high school physics class I asked the students to watch the following video on speed and velocity before class.

I also sent them the link to this video by Smarter Every Day on ice skating, since the textbook we’re using, How Things Work: The Physics of Everyday Life, uses ice skating to start talking about motion and forces.

I started class with an inertia demo and I had 5 of them so they could all try it while waiting for everyone to arrive.  All you need is a bit of cardstock (or file folder) cut and taped into a loop, a narrow mouthed jar, or water bottle and a lego block, nut or other small object.  I got this idea after browsing Steve Spangler’s website where you can actually buy the inertia challenge as a kit.  By putting a finger or two inside the loop and moving them quickly to the side you knock the paper loop away and the lego will fall into the bottle.  The lego falls straight down because you are only exerting a force on the loop of paper and once its gone there is nothing to hold up the lego and it falls into the bottle.  This is similar to pulling the table cloth out from under dishes, but not quite as messy if you do it wrong.

After a discussion on speed, velocity, scalars and vectors, I showed the students how to use the Video Physics app to record the motion of objects.  Since we were interested in constant velocity I set up the air track and glider and had an air-powered soccer disk (basically a small hovercraft which glides across the floor) which they could use.

The meterstick in the movie is used so you can set a scale in the Video Physics app. You can also set the origin for your coordinate system. The app can then graph distance as a function of time with the correct units (if you did it right).  Data can also be exported to Graphical Analysis app where you can tweak the graphs and make them look nicer for printing.  I had the students make one graph by hand so they could learn how to do it.

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Graph of position vs time.  Label for position didn’t make it into the photo.

If the object is moving with a constant velocity the data points will fall on a line. Students used a ruler to draw the best line through the data points and can calculate the velocity of the object by finding the slope of the line.

Below is a frame grab from a movie of the glider moving with constant speed on the air track. The red dots indicate the position of the glider at equal time intervals (each frame of the movie) and since they are roughly equal distant from each other we can conclude the glider is moving at constant speed.  For a more detailed description of this set up please see my post from the first time I taught this lab, Homeschool physics 003.  Next week we’l doing 1.2 in the text, falling bodies.

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SF Physics 01

61WL9w2qakL._SX377_BO1,204,203,200_I’m teaching two physics classes this year, a high school class, which I already posted about and a middle school class which I’m going to call SF Physics since we’re using the Science Fusion books (Module I & J). You can get a pretty good deal for the homeschool package, which includes the book and online access, through the Homeschool  Buyer’s Co-op.  If you just want the books, they can be found for  $6-$15 on Amazon.

The Science Fusion homeschool package gets you get online access to the teacher resources, which includes lab activities.  The books are colorful paperbacks, fairly thin (less intimidating then a big heavy textbook) and almost like a workbook, with many pages where the student is asked to answer a question or write on a diagram as they go through the chapters.  Today we did we did two activities, one investigating frame of reference and the other involved building a lego car and measuring its average speed as it traveled down a ramp.  throwing ball

The first activity, Quick Lab: Investigate Changing Positions, had students walk while tossing a ball up and down.  They sketched the balls apparent motion on the worksheet and then they watched their lab partner walk while tossing the ball.  In the second part they could see the ball moving forward as well as up and down.  One pair of students recorded the motion with the Video Physics App from Vernier and you can clearly see the motion of the ball marked with the red dots. When taking these movies the camera needs to stay still.  Here’s the movie, with the data points marked.  You can clearly see the forward motion of the ball as well as the up-down motion.  But the girl throwing the ball only sees the up-down motion because she is traveling forward with the ball.

The second activity, S.T.E.M. Lab Investigate Average Speed,  involved building a small lego car that would roll down a shallow ramp.  We used white marker boards propped up on thick books at one end for our ramps.  Once they had a working vehicle they used a stopwatch (usually an app on an iPhone/iPad) to record the time it took for the cars to travel down the ramp.  They repeated this measurement four more times and calculated the average time.  To find the average speed you need to know the distance traveled so they measured the length of the ramp with a meter stick.  Finally they calculated the average speed of the car by taking the distance traveled and dividing by the average time.  Most cars took about 2 seconds to travel 89 cm which gives an average speed of roughly 45 cm/s.  We discussed how this was the AVERAGE speed because the car starts with zero velocity at the top of the ramp and gets faster and faster as it goes down the ramp.  Before we did any of the activities we talked about the average velocity of traveling to Oregon for the eclipse – its 550 miles from where we live and if it took 10 hours than our average speed was 550 miles/10 hours = 55 miles per hour.  I asked them if that meant I was going 55mph the entire trip and we discussed how the speedometer shows your instantaneous speed which is always changing.  We also talked about the difference between scalar (magnitude) and vector (magnitude and direction) quantities.  If we were giving directions to someone and said go 2 miles to get to downtown… that’s not really very helpful, we need to say go 2 miles East or 2 miles NE.  Or if you tell say something is going 10 m/s (speed), that doesn’t really tell you to much, but if you give the velocity, 10 m/s North, now you know where its going, assuming you knew the original location.  Next week is lesson 2, acceleration.IMG_1819

Round 2 – High School Physics 01

UnknownThis is my 2nd time teaching a high school physics class for homeschoolers, many of the labs will be the same but I will continue to post after each class this year, even if its just to point to a previous post.  We’re using “How Things Work: The Physics of Everyday Life” by Louis A. Bloomfield, which is an algebra based physics text.  The majority of the students are freshmen.

Before class I recommended students watch the following videos (and observe the eclipse that occurred the day before class).

The Map of Physics which gives a nice overview of Physics.

A clever way to estimate enormous numbers by Michael Mitchell – which describes Fermi estimates.

And a Crash Course Chemistry video on Unit Conversion & Significant Figures.

I gave the students a handout on lab notebooks and lab reports and had them label the first page of their lab notebook as Table of Contents.  Lab notebooks are the student’s proof of doing real scientific labs which is especially important for homeschool students.

The lab today was pretty much the same thing I did last time, estimating the length of a hallway, measuring it with their feet (not a ruler, but their actual feet) and then with a meter stick.  Last time I had them use hand spans but this was a longer distance so I had them use their feet, heal to toe.  We talked about the sources of error, out lying points (1 measurement was off by almost exactly a meter so they probably mis-counted), calculated the average of everyone’s measurements and made a histogram of the feet measurements.  You can check out a more detailed description on the original post on metric units and measurements.

I also had them do some worksheets in class on scientific notation and significant figures.  Next week we’l look at speed, velocity and acceleration, Chapter 1.1 in How Things Work.

Watching the Solar Eclipse

We didn’t travel to see the eclipse but did get to see 75% of the sun blocked by the moon and the morning fog burned off just in time to make it visible.  We had eclipse glasses, cheap cardboard ones and some plastic ones, as well as pinhole box viewers, telescopes with solar filters and binoculars set up to project the image.  My younger son even used a  saltine cracker as a pinhole projector.

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Pinhole Saltine and image projected from binoculars (one lens is blocked).

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Televue Ranger telescope with solar filter – note the fancy coffee can adaptor.

As the sun was coming back out we got a nice view of the sunspots through the telescope and projected by the binoculars

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Sunspots visible near the end of the eclipse.  Image was projected on a whiteboard from binoculars.

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I also used my new Go Direct Temperature Probe from Vernier which connects to my iPad to take temperature readings in the shade for an hour before and an hour after the maximum eclipse.  This was part of a citizen’s science project by the Globe Observer program/App.

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The iPad showing the Globe app and some of the data I had taken so far and the iPhone shows the Vernier app, Graphical Analysis, which is used to read the temperature probe shown in the photo below.

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Temperature and Cloud data taken during the eclipse.  Maximum coverage of the sun occured at 10:15am.

We had a pretty heavy marine layer/clouds until about 9:30 which kept the temperatures down this morning.  But you can see the temperature dipped a bit as the eclipse started and the clouds were burning off so I think there’s definitely a decrease in temperature caused the eclipse.

Great morning full of science. I’m a bit envious of everyone who was in the path of totality but we just had too obstacles for traveling and it was nice being able to just step outside and view it in the backyard.  We did notice that in 2024 my parents house will be in the path of totality, as will Kenyon College, where both my husband and I got our bachelors in Physics AND UT Austin where we attended grad school will also be in the path, so we’l try to make it to one of those!

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Photo of sunspots near the end of the eclipse, taken by Craig Siders.

Solar Eclipse Class

With the upcoming solar eclipse I decided to teach a class for local homeschoolers and it filled so fast I ended up teaching three classes!  I started out by talking about the scale of our solar system and showed them this picture of the planets and asked them what was a57f24789eed987c20c6bce24542783dwrong with it.  Many realized the size of the planets was all wrong compared to each other and the sun.  The distances are obviously wrong as well since the planets are very far the sun and they are not equally spaced.  To make a model of the solar system to scale, I have a large exercise ball which is half a meter across and we used that as the sun. I then asked the students what size they thought the Earth would have to be for our model.  A few kids thought baseball size, a few thought it should be the size of a quarter, but its actually only 0.46 cm across!  I then asked the students where should we put the earth if we want our model to be accurate?  Should it be right next to the sun (green ball)?  A few feet away?  In the kitchen?  It needs to be  at the end of the culde sac across the street!  IMG_0757This kind of blows their minds because its sooo small (the tiny blue ball in the photo to the right) and needs to be so far away to be to scale.  The other planets are shown to scale with the sun in the photo – but not the right distances.  I showed the kids images of my house on google earth with the orbits of the planets drawn on it to scale and for the furthest planets we needed to be looking at a map of the city.

The photo below from wikipedia shows the planets to scale in size but the distances are not correct.  Its pretty much impossible to show both the size of the planets and distances in a meaning image that will fit on a piece of paper.Planets2013.svg

The first activity we did was to make a model of the Earth and moon to scale.  We used 1inch foam balls (painted blue and green) for the Earth and 1/4 inch pony beads for the moon.  The ball and bead were put on toothpicks and then clamped with bulldog clips to a square dowel (36 inches long, 1/4 inch wide) 30 inches apart.  This is roughly to scale.  We then went

outside and used the real sun (if it wasn’t cloudy) as our light source.  Students were able to make lunar eclipses (photo on right), where the shadow of the earth covers the moon and solar eclipses (photo on left), where the small shadow from the moon makes a small dot on the Earth.  We talked about how to see the solar eclipse you have to be standing in the shadow (the black dot on the earth ball, but to see a lunar eclipse you just have to be on the night time side of the earth.  This activity can be found in the Solar Eclipse Activity Guide put out by NASA.

IMG_1483Students also made pinhole viewers (directions can again be found in the NASA guide above). Basically you put two hole in one end of the box and tape white paper inside the other end to be your projection screen.  Then you cover one of the holes you made with foil and using a tack make a very small round hole in the foil.    To use the pinhole viewer you stand with your back to the sun, let sunlight enter the pinhole and fall on the projection screen while looking through the other hole that you made.

Students also made eclipse art, yet another activity from the NASA guide.   For this you hold down a circle of cardstock on top of dark paper and then draw around the circle with oil pastel (or chalk) and then using your fingers, smear the pastel outwards to make a corona.  The kids made some great eclipse drawings with this method.

Each student was also given a pair of solar eclipse glasses to take home so they can use them to watch the eclipse.  I actually bought some plastic onesfor my family so they fit over regular glasses and stay on better (update: just got notified that these might not be safe so Amazon refunded my money). The cardboard ones tend to fall off so you have to hold them on.   IMG_1485

Here’s some great videos on solar eclipses.

 

 

 

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