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R2 Physics 14 – Buoyancy

Students were asked to watch the following videos and/or read 5.1 Balloons in How Things Work: The Physics of Everyday Life.

And lastly Smarter Every Day, does a cool experiment with a balloon in his car.

While we waited for everyone to arrive for class I gave students large syringes with mini marshmallows inside.  By plugging the syringe they then had a contained volume of gas. By compressing the plunger and decreasing the volume in the syringe, they increased the pressure and the marshmallow gets smaller (kind of looks like a raisen).  As they pull out the plunger, increasing the volume of the gas in the syringe, decreases the pressure on the marshmallow and it expands.  Make sure students keep a finger over the plug to keep it from shooting across the room.

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I also crushed a few soda cans with air pressure – you can see a description and video in my previous post on buoyancy and pressure.    For the main activity we tried to measure the buoyant force on a floating object.  I had two large plastic containers with overflow spouts in them, and we filled them up until water started pouring out the spouts.  Once the water stopped coming out, students placed their objects in the water, which caused the water level to rise and overflow.  The overflow was captured in a container and IMG_3475students either measured the mass of the water that was displaced or they measured the volume and calculated the mass from the density.  They then compared the weight of the object floating in the bath to the weight of the water displaced.  They should have been the same and were in a few cases but many were off by 30-50 grams.  It was pretty evident that surface tension was a problem in our overflow spout, so cutting down the pipe we were using, or putting a little bit of dish soap in the bath would help with that.  having a smaller bath – smaller area on top might have made it more accurate as well. One group tried placing a 45 gram boat in the water and no overflow occurred, so we definitely had a problem with the set up.  I may have to try again with just a regular bowl that I can fill all the way up to the top and collect the overflow in a basin and see if I get better results.

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SF Physics 11 – Static Electricity

We’re on Unit 3, Electricity & Magnetism in Science Fusion Module I, so I started class with a slide on static electricity and showed the following videos.

I happen to have a Fun Fly Stick so students played with that a bit and used the cheaper alternative, a balloon rubbed on their hair and a strip of thin plastic bag.  Got that trick from Steve Spangler:

 

Here’s some other cool tricks shown in the video below.  I set up a matchstick in a jar and had a PVC pipe the kids could use and we bent a stream of water with the PVC.

Besides ‘playing’ with static electricity, the students also did a lab from the Science Fusion curriculum, setting up a simple circuit with a battery and a light bulb.  They then tested different materials, plastic spoons, coins, paper clips, pieces of wood, etc, in the circuit to see if they conducted electricity.  I dug out our Snap Circuits kit to make this a little easier.  We actually have quite a few Snap Circuits kits, I highly recommend them for learning basic electronics.  There’s a nice student guide that explains things a bit better than the manual’s that come with the kits.

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Student completing a circuit with a piece of aluminum foil. The light is on, showing that the foil does conduct electricity.

Horrible Science has a good book on electricity, Shocking Electricity by Nick Arnold and illustrated by Tony de Saulles.  These books are good for the middleschool crowd.  I bought a whole set of Horrible Science books from Ray at  Horriblebooks.com.

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R2 Physics 13 – Kepler’s Laws

I started class with a slide show on Kepler’s Laws and gravity.  We talked about Copernicus, Galileo, Tycho Brahe and Kepler and their contributions.  Here’s Doc Schuster’s video on Kepler’s Laws:

For the lab activity I had the students draw ellipses using a loop of string and two tacks, as illustrated in the first video above. Students labeled one of the foci as the sun and then labeled the perihelion (point on the ellipse closest to the sun) and the aphelion (point on the ellipse furthest from the sun).  They then measured the semi-major axis (distance ellipse_eccentricity_1

from the center of the ellipse to the aphelion and c, the distance from the center of the ellipse to a foci.  The ratio of c/a is a measure of the eccentricity of the ellipse.

For the second part of the lab, I had plotted the orbit of Mercury, which is one of the more elliptical planetary orbits.  Students were to show that Kepler’s Second Law – a planet sweeps out equal areas in equal time holds for Mercury’s orbit.  At two locations, when Mercury is closest to the sun and furthest from the sun, they had to measure the radius of the orbit and the angle swept out in that time period.  From that they could estimate the area of triangular section of the orbit and found the two sections to be approximately the same.IMG_3287

For more detailed descriptions of these and related activities you can look at an earlier blog post.

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SF Physics 10 – Simple Machines

I started class by asking the students if they could name some simple machines – machines that make it easier for us to do work on an object.  They knew ramps, levers and pulleys but its a bit tougher to come up with wheel and axle, screw and wedge.  To demonstrate a lever, I placed a coffee can on its side on the table to act as the fulcrum and taped it in place.  I then place a meter stick on the coffee can and wooden block on one end of the meter stick.  I asked the students, how should I place the meter stick to make it easier to lift the block?  Should the fulcrum be near the block or closer to where I’m pushing down on the meter stick?IMG_3288IMG_3289

In the top picture you would have to exert a larger input force because of the smaller lever arm on the input side, while in the bottom picture you can lift the block with a smaller input Force because you’re using a larger lever arm.  The bottom set up has a larger mechanical advantage, M.A. = F (output)/F(input).

We did two labs from the Science Fusion curriculum, Mechanical Efficiency and Investigate Pulleys.  Both can be found under teacher resources for Unit 2, Lesson 3 in Module I.  For Mechanical Efficiency students set up a ramp, measured the length up the ramp and the height of the ramp.  They also measure the weight of a block with a spring scale and then measure the force required to pull the block up the ramp.    They  calculated the mechanical advantage of the ramp and then raised the ramp and repeated their measurements.  They also calculated the amount of work done in dragging the block up the ramp,Work (in) versus lifting the block directly to the height of the ramp,Work(out), and the efficiency of the ramp which is equal to Work (out) over Work (in).

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For the pulley lab, students first set up a single pulley and had a string attached to a block, passing over a pulley and then to a spring scale.  They found that to raise the block they had to exert a force equal to the weight of the block when only using one pulley.  But when set up a block and tackle arrangement as shown in the photo above, the force they had to exert to raise the block was less than the actual weight of the block.  They also measured the distance they had to pull the string and compare it to the distance that the block actually moved in both the single pulley set up and the set up with 2 pulleys. They calculated the mechanical advantage of both systems.

Here’s a nice Ted Ed video on levers:

And a video on pulleys by funsciencedemos:

It looks like he has videos other simple machines as well.  I just wish he would read the Newton side of the spring scale instead of reading the force in grams.

 

High School Physics Round 2 (R2)

UnknownThis class is in progress, 2017-2018, most of the students are freshmen and we’re using How Things Work: The Physics of Everyday Life by Bloomfield.

Round 2 – High School Physics 01 – homeschoolsciencegeek

R2 Physics 02 – Velocity – homeschoolsciencegeek

R2 Physics 03 – Falling objects – homeschoolsciencegeek

R2 Physics 04 – Archery & Ramps – homeschoolsciencegeek

R2 Physics 05 – Energy – homeschoolsciencegeek

R2 Physics 06 – Circular Motion – homeschoolsciencegeek

R2 Physics 07 – Friction – homeschoolsciencegeek

R2 Physics 08 – Conservation of Momentum – homeschoolsciencegeek

R2 Physics 09 – Hooke’s Law – homeschoolsciencegeek

R2 Physics 10 – Bouncing Balls – homeschoolsciencegeek

R2 Physics 11 – Paper Rollercoasters – homeschoolsciencegeek

R2 Physics 12 – Force of Gravity – homeschoolsciencegeek

R2 Physics 13 – Kepler’s Laws – homeschoolsciencegeek

R2 Physics 14 – Buoyancy – homeschoolsciencegeek

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