Category Archives: BFSU

Sci-Fri: Oobleck

This is something the boys have wanted to do since they watched this video on YouTube:

Most liquids follow certain properties and are known as Newtonian fluids (after Sir Isaac Newton). Today we had a super fun time learning about non-Newtonian fluids. I won’t try to go into detail about what Newtonian and non-Newtonian fluids are in this post because there are lots of sites on the internet that can explain that better and more completely than I can. But, very simply, non-Newtonian fluids behave differently than typical liquids because they have a variable viscosity. They behave differently depending on the amount of stress they are under. We made a cornstarch and water mixture that will flow like a liquid when resting or touched gently, but if put under more stress, such as a hard smack it behaves like a solid. Other non-Newtonian fluids are ketchup, silly putty, and toothpaste.

This is a really simple and fun activity for kids. We started with 1/4 cup of cornstarch in a bowl and added small amounts of water to it until we could stir it but felt some resistance. When you pick it up in your hands and squeeze, it will become more solid, but then when you open your hand it will flow like a thick liquid. Be sure to have extra cornstarch on hand if you need it for dinner, because we went through almost an entire box today. You can click on the pictures below for a larger view of our Oobleck as the boys played with it.

Sci-Fri: Non-newtonian fluid Sci-Fri: Non-newtonian fluid
Sci-Fri: Non-newtonian fluid Sci-Fri: Non-newtonian fluid

Sci-Fri: Non-newtonian fluid

I’m really glad I waited until the warmer weather because this is one experiment that I would not want to do inside the house.  Another note is that you don’t want to put this mixture down your drain, if there is any left-over stick it in a bag in the trash, after a while the water will be removed and it will become a solid again.

We did just the basics, but if you are brave and have an extra sub-woofer lying around, try putting the cornstarch mixture on the sub-woofer, turn on some bass beats and watch the show. Make a few small batches with different colored food-coloring to see how the colors mix. Even if you don’t teach the science behind it, kids love this stuff. So go ahead, give it a try!

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Sci-Fri: Inertia

Our science lesson today in BFSU was Newton’s First Law of Motion, namely: Inertia!

In physics, Inertia is the law that, simply put, states: “an object in motion tends to stay in motion, while an object at rest tend to stay at rest.” My objective was to expand on our earlier lessons on matter and energy and help relate these concepts to real life.

The Lesson:

We started off with two activities that the kids could have some fun with. The first was the old tablecloth trick, except that I don’t have a tablecloth so we did it with a glass of water and a piece of paper. This trick demonstrates the first part of the law of inertia, “an object at rest will stay at rest unless an outside force acts on it.” When the paper is yanked out from underneath the glass there is not enough force to break the inertia of the glass so it stays put. We also observed that if you move the paper more slowly the glass will move with it, but of course this is due to friction between the paper and the glass. We discussed the idea that every day objects don’t go zooming around unless someone or something has acted on them. If a toy is left on the floor, we can expect it to still be there an hour later unless little brother has moved it. This part of inertia is fairly easy to understand so we moved on quickly.

Our next activity was a game involving a bean bag held at shoulder height and a target bowl placed on the floor. The kids had to run past the target and drop the bean bag at just the right time, without stopping, so that it falls into the bowl. The trick is that the bean bag continues to move forward after it is dropped so that it must be dropped early to hit the target. To better illustrate, I had the boys stand next to the bowl while I did the activity. From that angle they were able to observe that when I dropped the bean bag it moved diagonally rather than straight down.

We discussed how this game illustrates the second part of Newton’s First law “an object in motion will continue moving in the same direction and at the same speed, unless another force acts on it.” Of course on Earth objects do not continue moving indefinitely because we also have gravity and friction to take into account. I like to start by thinking about how objects in space behave to better illustrate what it really means to “keep moving in the same direction at the same speed.” If we could toss a tennis ball in open space we could clearly see this principle. Unless the tennis ball encounters a gravitational field or another object it will move forever through space in the same direction. Astronauts who perform maintenance outside the International Space Station wear a tether line for just this reason. Objects behave differently on Earth primarily because of gravity and friction. We talked about every day ideas such as why we trip forward instead of sometimes tripping backwards and why seat belts are required in the car.

The boys had fun with these ideas, attempting to trip backwards and finding that they could only do so by either walking backwards or changing their center of gravity as they fell forward. Somehow our discussion of cars ended up with us yanking chairs out from under each other.

THE EXPERIMENT:

After finishing up our discussion I thought it would be fun to give EJ some free reign to choose an experiment for him to perform to demonstrate the concept of inertia. I helped him do a search for inertia experiments on YouTube and told him to pick one that he knew we had the materials for, to set it up and call me when it was ready to go. First, he tried to pick a vacuum experiment involving a candle which of course is interesting but has little to do with inertia. Finally he chose the Egg Drop. It worked perfectly as you can see in our video.

As always, thanks for reading!

Science: Kinetic and Potential Energy part II

This is part II of the science lesson on Potential and Kinetic Energy I did with EJ (7) and JD (5). It is based on lesson C-3 in the book Building Foundations of Scientific Understanding by Bernard Nebel. If you missed part one it can be found here.

Let’s go Bowling!

After our lunch break, we talked about a phenomenon the boys had observed at the bowling alley. Bowling is an excellent and fun real world physics lesson!

The boys enjoy waiting for their bowling ball to come out of the ball return. One day there were several unused balls lined up on the return when EJ’s ball appeared and knocked into the first ball setting only the final ball in the line moving; the others remained stationary. They thought that was super cool! At the time my husband discussed what was happening with the balls but I wasn’t sure how much they retained.

We re-created this scenario with some 1″ steel ball bearings I found at a surplus store. I lined up three of the bearings and asked EJ if he could make the last one in line move without touching it. Then I asked him to explain what was happening. He recalled that energy cannot be created or destroyed and therefore the kinetic energy from the first ball had to have been transferred into each subsequent ball in the line. He understood that the other balls couldn’t move because they were blocked by the next ball until finally the last ball was free to use the kinetic energy it received from the first ball.

EJ then devised his own little experiment using the steel balls and a kids chair from Ikea. He created a hyperbolic funnel, sort of. I’m sure everyone has seen those coin funnels that are used for fundraising, usually in science museums. These funnels are essentially a working model of our solar system. How cool is that! This was not part of our lesson plan so I just let him play as we ended part 1 of our lesson.

Plants and Animals

Finally on day two we completed our final objective of the lesson. We needed to relate what we’d learned about energy back to life on our lovely planet Earth. Previously we had discussed the primary difference between the Animal Kingdom and the Plant Kingdom. Namely, that plants make their own food through photosynthesis and animals must eat plants (or other animals) for food. The kids know that plants get the energy they need for photosynthesis from the sun’s light. They also know that light is one form of energy. Now I asked them to put it together and tell me what KIND of energy the light from the sun is. EJ was able to identify that sunlight is kinetic energy, that the sugar was potential energy, and that when we eat the plant we are transferring, or using, its potential for energy into our bodies to do work i.e. kinetic energy. Eureka!

I couldn’t help but extend this part of our lesson even further by asking EJ where he thought the sun got its energy. We discussed that the energy of the sun is chemical energy produce by the reaction of gasses, particularly hydrogen and helium, causing them to burn. Where did the gas get its energy? Where did the energy that caused the big bang come from? These questions are beyond us at this time, but I used the line of questioning to further reinforce the idea that energy is not made, that it is merely transferred from one thing to another.

This questioning also helps to illustrate an important point about scientific discovery. Specifically, that it’s okay that we don’t have all the answers and that THAT is what science is all about! The continued search to discover and explain how our world and universe work.

Science: Kinetic and Potential Energy

I thought I’d take some time to write about one of our recent science lessons using Building Foundations of Scientific Understanding, or BFSU. This is going to be long so I’ll post it in two sections.

In a previous lesson we discussed energy and its basic forms of motion, light, heat, and electricity. We have also covered gravity and to a lesser extent friction. This week we were to expand on that topic in lesson C-3 Concepts of Energy II: Kinetic and Potential Energy.

I started the boys off with some videos of roller coasters from the Discovery channel series Build It Bigger. Then we moved on to two videos the boys have seen before from a series they ask for often: Eureka! EJ at 7, probably understands physics as well as I do just because of this 30 video series. Highly recommended.

While they watched I set up the activity room with some demonstrations to help illustrate kinetic and potential energy. We had a pendulum hung from the ceiling, some rubber bands, balloons, 4 large steel ball bearings, and of course a marble coaster. They played for about 15 minutes before we sat down to discuss each item.

First we defined our terms:

  • Kinetic Energy: The energy of movement.
  • Potential Energy: Energy that is available to be used as kinetic energy.

One of our objectives was for the kids to understand that an object’s potential energy depends on whether it has the right position and condition for energy to be present. Discussing the Eureka! episode on potential energy I asked the boys if the rock on top of the cliff had any energy. They understood that it did have energy because it was in a position where gravity could act on it causing it to fall and make work. Yay! As an aside, because they understood that so easily, I asked them to consider how the rock got up to the cliff in the first place. That was a bit trickier which is just as well because it leads to our next objective!

Next we had to learn that an object does not have energy unless energy has been put into it. As we played with the marble coaster we identified that a stationary marble on the floor has no potential energy due to its position in relation to the vertical pull of gravity.  I slowly moved the marble from the floor to the top of the coaster asking questions about what I was doing in terms of energy. EJ was able to state that I was using some of MY energy, transferring it to the marble. We discussed this with each demonstration until it became clear that energy must be put into something before we can get energy out of it. Then we discussed the coaster in terms of kinetic energy. As the marble rests at the top of the coaster it has potential energy and once it begins to travel down the coaster it has kinetic energy. We also discussed why the marble eventually stops and related this to what we know of space where there is no friction and low gravity.

Next we focused on the concept that ENERGY INPUT = ENERGY OUTPUT. As I held up the weight at the end of the pendulum I asked whether we could predict how high up it would swing to the other side when I let go. Would it go higher, the same height, or lower? JD though it would go higher while EJ said it would swing to the same height. EJ had the right idea, he felt it would go the same height because of the amount of energy that was transferred into the weight by my lifting it. He forgot however, that there is another force acting on the weight, namely friction.

Before breaking for lunch we listened to a silly little song called, what else? Kinetic and Potential Energy! Then they played with two online illustrations of energy in roller coasters. Eduplace’s Energy and Motion simulation, and Fetch! With Ruff Ruffman’s Whoaler Coaster! game (another absolute favorite in this house).

Stay tuned for part II coming soon!