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SF Physics 13 – Mini Motors

We did a few different activities today.  I had out the snap circuits and had students build a series circuit with 2 light bulbs and then use the same light bulbs in a parallel circuit.  A series circuit is bascially one big loop. series parallelThe current flows from the battery and through each lamp in turn before returning to other end of the battery.  In a parallel circuit, the current splits up and some goes to each lamp separately.  If one of the lights fails, in the parallel circuit the other light will still light up because you still have a closed circuit. But in the series circuit, if one bulb breaks, then the circuit is open and currently can’t flow through the loop.

To show students that an electric field can also make a light bulb glow, I put an old fluorescent bulb near a plasma toy and parts of it would light up, as seen in the photo below.IMG_3672

Lastly we made mini motors with 28 gauge copper magnet wire.   Wind 15 to 20 loops around the end of a fat marker to make a coil, leaving about 10 cm of wire on either end of the loop.  Take the ends of the wire and wrap them around the sides of the loop once or twice to hold it together, then take sandpaper and rub off the insulation on the wire sticking out from the coil.

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You need to get the insulation off so the wire can make a good electrical connection with the paper clips.  Paper clips are bent so they can support the coil and are taped withelectrical tape, to each end of a battery (C or AA work fine).  Place a magnet under the coil loop and then give the coil a flick and if you have everything positioned just right it will keep spinning – see the video below.   I got this lab from Teaching Physics with Toys.  I used this book a lot when my boys were younger.

It can take some fussing to get this to work right.  You have to make sure the insulation is off the ends of the wire and you want it to be pretty close to the magnet.  If you have a variety of magnets you might test to see which ones work best and how close the coil loop needs to be to the magnet to keep it spinning.  This class is small enough that I let them take home the mini motors if they wanted to.

This is the last class til after winter break.

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SF Physics 12 – Holiday Circuits

Instead of doing the usual circuits lab I decided to have the kids make light up holiday cards.  Fortunately I found this great website on Sparkfun with templates you can download for FREE and I still had some LEDs left over from the last time we did this years ago.  You can order all the stuff to do these from Sparkfun, but I just happened to have the lights and button batteries.  I did not have copper tape but that got me thinking… can’t we just use aluminum foil?  So a little searching on the internet and yes, people use foil for this as well.

The lights I used were from 15 piece “Gumdrop” LED assortment from Evil Mad Scientist, that I had picked up at the Exploratium.  Amazon also sells LED, and you can probably pick them up at Radio Shack if you’re lucky enough to still have one near you.

Here’s my card and the aluminum foil circuit inside.IMG_3545IMG_3581

I didn’t have the button to turn it off or on or the fancy button holder.  I just put a little piece of scotch tape around the side of the battery to keep the loose piece of foil from touching both the top and bottom of the button battery (short circuiting).  When you squeeze the card over the button battery it closes the circuit and lights it up.

A couple of the kids tried using the conductive paint but it was really hard to get a nice line of paint and it didn’t actually seem very conductive at all.  The foil was easy and you don’t have to wait for it to dry.  There was also a window template and light up gingerbread house.  You can also find robot templates or have the kids make up their own.

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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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.

 

SF Physics 09 – Potential & Kinetic Energy

We started class today by going through some of the exercises in the Science Fusion Module I workbook, Unit 2, lesson 2.  I had lectured last week about the difference between potential energy and kinetic energy so it was a good way to review.  There are some simple problems where the book gives the mass and speed of some horses and you have to calculate their kinetic energy by just plugging into the formula, KE = 1/2 mv2.

pendulumWe did the Quick Lab, Identify Potential & Kinetic Energy found on  the online teacher resources.  There’s no measuring in this lab, its purely observing three different situations, making some sketches and then labeling when the object has the maximum potential and kinetic energies.  First they just drop a ball.  At the top before they release the ball, all its energy is potential energy, but when they release the ball it falls to the ground, converting potential energy into kinetic energy.   The second set up was a pendulum.  The watch it swing back and forth a few times and I asked them what was the pendulums speed at the top the swing, when its turning around? Zero.  So what is it kinetic energy at that point? Zero.  All the energy is potential energy at the top of the swings and its all kinetic energy at the lowest point of the swing.

Lastly I had a spring hanging with a weight on it.  The students stretched the spring, giving it elastic potential energy, which is converted into kinetic energy when its released and then back to potential energy and so on.

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We still had some time so students made flipbooks demonstrating kinetic energy, pendulum swinging back and forth, fish swimming across the page, ball dropping, etc.  I also had them complete the table on page 95 for a basketball.  Most of the table was filled out, giving the potential, kinetic or total energy of the ball at various positions during a throw.  Students were able to finish the table and they all seemed to have an ‘aha!’ moment when they saw that the total energy was always 18 J

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