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# homeschoolsciencegeek

### October 2017

Section 3.3 Carousels & Roller Coasts in How Things Work, the Physics of Everyday Life.  Students were to watch the following videos before class.

Today’s class happened to fall on Halloween so the students ate sugar and built paper roller coasters. I bought the templates off paperrollercoasters.com a few years ago and this was the first time I really used it in a class.  It takes a lot of time to cut out the pieces, score them, fold them and tape them in place so I divided the class into two teams, 5 kids each. I figured that was enough kids to get a decent number of pieces built.  As the two hour class started to wind down the building became frenzied and a bit sloppy but both teams managed to build coasters that fulfilled the requirements: 1.5 m of track 1 loop, 6 turns, at least 30 cm high, decorations and a bucket at the end to catch the marbles.

When they were finished they measured the time it took for a marble to complete the ‘ride’.  The Cupcake coaster above took 8 seconds to reach the funnel at the bottom but another 8 seconds before falling into the bucket.

The Purple Terror above had a ‘ride’ time of 8 seconds, including nearly verticle drop shaft.  This coaster also had warning sides, ride at your own risk.

Gauging from the laughter as the teams tried to out build each other, occassionally pilage parts and shouts of delight as the marble actually made it down the track and around the loop, this was a fun class.  But if I were to use it in class again, I think having 3 to 4 hours would be better, or 2 class periods.

Many students brought in treats, including these amazing cupcakes.

We spent the first 40 minutes of class going through a slideshow about work and power.  We discussed that doing work in physics means exerting a force on an object over some distance.  But the force has to be in the same direction as the displacement.  If you are pusing a large box across the floor, the further you push it, the more work you do.  The heavier the box, the bigger the force you need and you do more work.  But if you are holding a tray of food on your hand, the force you are exerting is an upward support force, so unless you are lifting the tray, you won’t be doing any work on the tray if you just walk around a room with it at the same height.   To do work on an object the force has to be along the direction of displacement.

For this class we used the Calculating Power Lab from Science Fusion Module I, Unit 2, Lesson 1.   Students took a shoe box and hung it from a spring scale.  They then added things to the box until the force on the spring scale was 2 N.  Then they dragged the box up a wooden plank so it raised the height of the box 0.5 meters.  One student dragged the box while holding onto the spring scale, while another student attempted to read the force on the spring scale and another student used a stopwatch to measure the time required to pull the box up the ramp.  Students repeated this experiment with different weights, so they had measurements for 2N, 4N, 6N, 8N.

Once they had all the measurements, they calculated the work done by multiplying the weight of the box (plus all the stuff inside it) which is equal to the force required to lift the box, times the height the box was raised by pulling it up the ramp (0.5 m).  So for the first round, W = F x d = 2N x (0.5m) = 1 Nm = 1 J (Joule).  You can then calculate the power, P = Work/time, which is how much work you can do per unit of time.  If you plug in work in Joules and seconds for time, then the unit of power will be Watts, 1 Watt = 1 J/s.

Students then repeated the experiment with the ramp reaching a height of 1 meter.

Students read section 3.2 Ball Sports: Bouncing Balls from How Things Work: The Physics of Everyday Life and were asked to watch the following videos before class:

For the lab, students chose a ball (soccer, volley, superball, pingpong, etc) and dropped it from 4 different heights, 25, 50, 75 and 100 cm.  They used their phones and ipads to record the bounce so they could easily record the height reached by the ball after its bounce.  They did this measurement twice for each height and calculated the average.  They then graphed the height of the bounce as a function of the dropped height.  Each group did this with two different balls.    The ratio of this heights or the slope of the graph are related to the elasticity of the  ball.  If  we had a perfect ball, the slope would be 1 because the ball would bounce back to the height at which it was dropped, losing no energy to heat during the collision.  A ball that doesn’t bounce at all will have a slope of zero, so the closer the slope is to 1, the more ‘lively’ the ball.

At the end of class, students went outside and tried to do the stacked ball trick in the video above.  We hadn’t used a hot glue gun to make the stacking easier so the balls generally went flying in all directions but it was pretty clear that the balls on top were taking away more energy.

Here’s a video from a summer class I taught showing the stacked ball trick:

Students from both my physics classes went to iFly yesterday for some indoor skydiving and a short class on terminal velocity and drag.  I actually participated the first time we went to iFly… many years ago but this time I just took photos and movies.

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And some movies:

I highly recommend iFly for a homeschool fieldtrip.  They do a decent job of explaining the physics with demonstrations before hand and a bit of classroom time after the flights.  Its a bit pricey as far as fieldtrips go but its not everyday you get to go indoor skydiving!

Students were asked to read 3.1 Spring Scales in How Things Work, the Physics of Everyday Life and watch the following videos before class.

And the first 8 minutes of Doc Schuster’s video on simple harmonic motion:

The lab that we did was identical to what I did in the last high school physics class so I’m just going to link to that post. Physics 12 Hooke’s Law.   That post also has a few extra videos on this topic.  Because this is such a straight forward lab its a good one to have the students write up as a lab report.

HOLLYWOOD ( and all that )

hanging out and hanging on in life and the movies (listening to great music)

Learn from Yesterday, live for today, hope for tomorrow. The important thing is not stop questioning ~Albert Einstein

graph paper diaries

because some of us need a few more lines to keep everything straight

Evan's Space

Wonders of Physics

Gas station without pumps

musings on life as a university professor