Category Archives: Science Fridays

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!

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!

Sci-Fri

I’ve decided that Fridays will be our day for science. Although I may change my mind, because I do that a lot, the plan is for every other Friday to be a lesson from our BFSU curricula while alternate Fridays will be ‘fun with science’ day.

I really like BFSU and think the boys have learned a lot, even JD who is still a bit young for it. But I find the lessons to be just a bit short on WOW! factor. Our fun days will not necessarily relate to anything we are learning, they’ll just be (hopefully) fun.

This week we pulled out a birthday present EJ received almost two years ago!

Scientific Explorer’s Fizzy Foamy Science Kit of Safe Chemical Reactions

The kit comes with envelopes of baking powder, citric acid, colored fizzy tub tablets, yeast, and vegetable oil. There are also stirrers, mixing cups, a tiny magnifying glass and an instruction/explanation booklet.

The boys had a blast!

Fizzy Foamy Science

This was your basic citric acid solution with baking soda added. They both knew what was going to happen but as you can see by their faces it still enthralled.

We talked about how the bubbles are caused by a chemical reaction between the citric acid and the baking soda and that the bubbles are filled with carbon dioxide gas. After using the citric acid solution we did several experiments to see what other liquids might be acidic. We tried orange juice (mildly acidic), milk (not acidic), oil (not acidic), and of course vinegar (very acidic). They boys noticed that the vinegar caused many more bubbles than the orange juice. They also tasted a tiny bit of the orange juice and found that it was like orange soda (except for the blechy baking soda taste).

Fizzy Foamy Science

Next we tried the fizzy tub tablets.

The blue cup contains 1/4 blue fizzy tub tablet and water. They loved that it made the water turn blue and also fizzed. We talked about what might be in the tablets which turns out to be baking soda and citric acid. We talked about the fact that when the two ingredients are added together as solids there is no chemical reaction but as soon as we add water and allow them to dissolve the bubbling is released.

Then we made a “volcano”.  First we started with vegetable oil, then added water. This gave us a chance to talk about density and how the oil stays on top of the water in a layer because it is less dense. After adding the red tablet they noticed that the bubbles float up through the oil, but only the water became red.

Next we changed the experiment just a bit. First we added some red food coloring drops. This was really cool because the food coloring drops would remain suspended in the oil for several seconds to almost a minute before finally floating down to the water. Then we added baking soda and citric acid and watched as our volcano erupted again.

Fizzy Foamy Science

Next we did the “dancing raisins” experiment. This was one EJ had seen on Head Rush with Kari Byron (who can also be found on Geek Mom), as soon as I pulled out the raisins he knew what was going to happen. The raisins are denser than the water of course, and will sink to the bottom of the glass. As the citric acid and baking soda react, the carbon dioxide bubbles stick to the raisins. If enough bubbles stick, the raisins will float up to the surface. The bubbles then pop causing the raisins to drop back down to the bottom. They will do this over and over as long as your chemical reaction is happening which for us was at least ten minutes. We were pretty lucky that all of our raisins did dance.

After we finished our official experiments EJ went off to feed his lady bug and JD decided to mix up some solutions of his own. We even have a handful of fizzy tub tablets left so we’ll try them out in the bath tonight!

Although most of the ingredients are easily found in the grocery store, having the instructions really helped me keep the experiments going. The only issue we had was with the yeast which did not activate, but that was probably because we kept the kit for so long before using it. This is a fun kit that would be great for any kid from about 4/5 and up. I think we all enjoyed today’s SCI-FRI!