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# homeschoolsciencegeek

### June 2016

Today we talked about forces and Newton’s 1st and 2nd law.  We started with just a block sitting on the table and I asked the kids to describe the forces acting on the block.  Then they drew the block on a sheet of paper and labeled the two forces, gravity pulling down and the table pushing up.  Then I pushed on the block so it moved across the table and asked them again what forces were acting on the block and we drew another picture, adding the force of me pushing and the force of friction acting against that force.  The kids already had a pretty good understanding of friction and the fact that its what slows things down, so they had no problem with Newton’s 1st law, that objects at rest stay at rest and objects in motion want to stay in motion.

We did the lab “Inertia and You!” from Real Science Odyssey Physics where we had lego cars with minifigures sitting on top, but on flat plates, not connected with legos, so the figure was free to slide around.  The students guessed what would happen to the lego figure when they gave the car a push, wrote it down and then did the experiment.  As expected the minifig got left behind.

Then the kids added a few bricks to give the minifigures a backrest and did the experiment again. This time the car was able to push on the
lego figure and he went along for the ride.

The third part of this experiment involved crashing the car, bringing it to an abrupt stop and observing the motion of the minifigure. We talked about seat belts and airbags and other ways cars are designed to keep us from ending up like the minifigures.

Next the students tied strings to the lego cars and pulled them along on a smooth floor – exerted a constant force on the car.  They made observations on the motion/speed of the car.  This is Newton’s Lab #4: You’v Got to Keep it Moving!, from Real Science Odyssey Physics.

Lastly we played with the air track.  I set up a cart on the track with elastic bumpers so once its put in motion it just keeps moving back and forth along the track.  We used the Video Physics app to record the motion and saw that yes, the cart was moving at a constant speed since the red dots marking the carts position moved the same distance in every time interval.

Then I asked them what would happen to the motion of the cart if it had a constant force pulling on it (a string attached to it, going over a pulley and tied to a weight) and most of them answered correctly that the cart would speed up or accelerate

You can see that the cart was barely moving on the left side of the photo since the dots are right on top of each other, but as the cart moves to the right the dots get further and further apart indicating that the cart travels a greater distance with each time interval, its speeding up!

With my older classes I would have the kids take the data and analyse the graphs but these kids are pretty young so my son and I helped them take the data/videos and just talked about the pictures as I did above.  But even without using the app we could easily tell the cart was accelerating when there was a constant force acting on it.  I asked them what would happen if I doubled the weight on the end of the string, therefore doubling the force and they answered correctly that the acceleration would double. Then I asked, “What if we increase the mass of the cart?”, and they realized that would make it the cart harder to move so the acceleration would decrease.  So we figured out Newton’s 2nd Law, F=ma.

One other thing we did in class was play with these air hockey pucks (air powered soccer disk).  They’re battery powered and act like a mini hoover craft, shooting air jets out the botoom, so they shoot across the floor with just the smallest of pushes and show that Newton was indeed right, if we can get rid of friction then an object in motion will stay in motion.  The kids had a lot of fun playing with these.

Here’s a nice website by BBC with an interactive on forces.

For today’s class we did two different labs. The first one I found while digging for materials for the chemistry class I’l be teaching this fall.  This website, Middle School Science, has a great list of resources for middle school chemistry, including this activity for ‘bottles of stuff.’  I liked this activity because the kids get to bring in a bottle of stuff, they have to guess which ones are more massive and then actually estimate the mass of each bottle.  Since few Americans are familiar with grams, its a bit of challenge to guess the mass of a bottle of legos in grams so I gave them a big bottle that had a mass of 500 grams, a 50 gram brass mass and 5 gram cubes (each cube is a gram).  This helped them at least get the right order of magnitude.  Once everybody had their estimates the kids learned how to use a triple beam balance to measure the  actual mass of each container.  There were a few surprises, like the bottle of yarn actually had a smaller mass than the bottle of air, but the kids were quick to realize the bottle of air was bigger and made of thicker plastic and it had a larger cap.

When they were done making their measurements and ranking the bottles from lightest (least massive) to heaviest (most massive) we talked about their density a bit.  I asked them if they thought any of them would float and they thought they woud since they still had air in them.  One kid asked if we could test it out so I pulled out a big bowl and filled it with water.  They noticed the bottle full of cotton was almost entirely above the surface of the water but the very massive bottle of screws was almost completely under the water. This happens because the weight of the bottle displaces a volume of water that would equal the weight of the bottle.  The bottle of cotton only weighed around 20 grams so it only displaces 20 grams of water but the bottle of screws was over 500 grams and so it displaces over 500 grams of water.

The second lab we did was from the Real Science Odyssey Physics curriculum, Water Displacement: It’ll Float Your Boat!  Each kid was given a ball of sculpey clay about 1 inch in diameter and a cup of water.  They marked the level of the water on the outside of the cup with a whiteboard marker.  Then they dropped their ball of clay in the water and marked the new level of the water.  The water line went up since the clay was taking up space in the cup.  Then they made different shapes and tried again.  The water always came back to the same level.  After doing that a few times they started making boats that float and saw that the water line was still the same!

My son, Charlie, who’s helping with the class shared this video by Steve Splanger where he floats an Aluminum foil boat on what looks like regular air, but its actually a very heavy clear gas called sulfur-hexafluroide.

We didn’t show this in class but here’s a Bill Nye video on buoyancy where they do a similar activity with clay boat vs ball and measure the actual amount of water displaced and show its the exact same for both.

My younger son, Jake, 13, plays piano and cello and started composing music on his iPad  this past year.  Earlier this month he did a movie making camp for young kids and made the music for the entire short film.  I was pretty impressed by the film considering it was 4 kids, 2 of which were 8 years old and they only had 4 days to write and shoot it.   Jake had to stay up most of Thursday night to finish the music.  Enjoy.

Here’s a link to Jake’s movie reviews – he created this website all on his own last year after doing a bravewrite movie club and adds to it a couple times a month.

Whenever I teach a new group of students I always like to start with a measurement lab to get them thinking about how they measure something and what it means when right down a measurement.  We talked about units a bit and how metric units are easier to work with then units like feet and inches (width of your thumb) and I put my poster about forbidden 4-letter words (inch, mile, etc) back up on the wall.  I didn’t make this poster but I love it.

I asked the students (8-12 years old) to estimate the length of my kitchen table (if I was in a classroom I use the length of the chalkboard).  The chalkboard or something longer like a fence or the side of the house works a bit better because they really have to think about how many meter sticks would fit across it, while the table was pretty clearly near 1.5 meters which is what they all estimated.

Then we measured the length of the table in hand spans – length from pinky to thumb with your hand stretched out. If you’ve read my other physics posts this might all seem familiar, like I said, I do this in the beginning of most of my science classes. The kids counted how many hands it took to go down the length of the table and answers varied between 8 and 13.  We discussed why the answers were so different – different sizes of hands, some kids actually used their hand in a different orientation, miscounting, etc.  We also talked about why its important to put units on a measurement,  saying the table is 10 long doesn’t tell us anything, 10 ft? 10 inches? 10 cm?  Units are important! I also asked them how sure they were of their measurement.  Would they bet \$50 that if we brought in another kid and they measured the table they would say it was 10 hands long?  They all said no, and that they didn’t have that kind of money to begin with.  But then we measured the table with meter sticks to the nearest mm and they were willing to bet \$50 that someone else would measure the table and find its length to be between 1.62 and 1.63 meters long.  I told them when scientist report measurements they also put an uncertainty on their measurements so we can tell how precisely they measured it.

Then we moved on to Weighing In Around the Solar System from the Real Science Odyssey Physics curriculum.  We talked about the difference between mass and weight and they seemed to have a pretty good grasp on weight and knew it was caused by the force of gravity, one kid even knew that his weight on the moon was going to be 1/6 of his weight on Earth.  We then watched the following Veritasium video on mass vs weight.

We also talked about the vomit comet (plane which flys in a parabolic orbit to simulate free fall – zero g)  for awhile when one kid mentioned zero gravity, so I had to show this amazing music video by OK Go which was filmed entirely in a vomit comet with no special effects except PHYSICS.

I didn’t show this in class, but its a nice explanation of the vomit comet and weighlessness.

For the lab the kids just had to measure their weight using a scale and then calculate their weight on different planets.   We talked about how the bathroom scale was measuring the force of gravity pulling you towards earth and that it would give a different answer if we were to use the same scale on the moon or another planet.  I also showed them a balance and how it measures mass by comparing the unknown mass to known masses and how it would give the same answer anywhere.

When they were done filling out the table they were a bit wowed by the fact that they would weight around 2000 lbs if they could stand on the surface of the sun and that their weight would not be all that different on Saturn, which is huge, but its not very massive.  The Exploratorium has a nice website , Your Weight on Other Worlds, where you can type in your weight on earth and it shows you your weight on the other planets, moons and even stars!

We had a few extra minutes at the end of class so we watched the Brainpop on Measuring Matter. If you have kids younger than 13, you really should invest in a subscription to Brainpop, my kids loved it when they were younger.  The videos are great and they have them on all kinds of subjects. My youngest used to watch a few brainpop videos every night before bed, for years!  You can watch them on ipads, or if you use a desktop you can watch the videos, play games and find activities/labs to do as well.  Well worth the \$100 a year.

Over Memorial Day, Pandia Press had a sale on their curriculum and I couldn’t resist buying the Real Science Odyssey (RSO) Physics Level 1.  My kids are way too old for it but whenever I talk about my science classes in the local homeschool community its always the parents of 8-10 year olds that are the most interested in science classes. So I bought it and we start the class tomorrow.  Physics is the easiest subject for me to teach, having taught it at the college level and many times over the years as a homeschooler, so it shouldn’t involve too much prep work and I can usually just go with whatever RSO suggests as an activity.  Previously, I’ve had to adapt or change some labs/lessons because the kids would have already done them, but this class is a whole new crop of kids so we’l just start at the beginning and work our way through.  As with my other classes I’l post what we do each week.

I’ve also started working on the fall science classes.  We’re going to do High School Chemistry using Chemistry the Central Science by Brown (12th edition – not the latest edition, so we can get it cheaper) and the middle school class will use the free Middle School Chemistry curriculum by the American Chemical Society.  I’l post more about those as I get my crap together.

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

George Lakoff

George Lakoff has retired as Distinguished Professor of Cognitive Science and Linguistics at the University of California at Berkeley. He is now Director of the Center for the Neural Mind & Society (cnms.berkeley.edu).