Stopping color in its tracks

This experiment was hard to pull off, but very cool once we got it to work. Since salt water is denser than fresh water, you should be able to get fresh water to sit on top of salt water, rather than all mixing together. The idea is that you put clear salt water in one container and fresh water with food coloring in another container. When you poor the colored water into the container with the salt water, the colored water should sit on top of the salt water, giving the appearance that you've stopped the color in its tracks. The only problem is that the force of pouring the colored water makes it go to the bottom of the second container before rising to the top, coloring the salt water in the process. Remembering how we got a paper clip to float using surface tension, we floated a piece of cardboard on top of the salt water and carefully poured the colored water onto the cardboard. The trick worked - although we had one attempt where some of the colored water missed the cardboard, greatly diminishing the wow factor. But when it worked, it was surreal.

Turning salt into glue

We tried to pick up ice cubes with string, using salt as the "glue." The idea is that, when you put salt on ice with the string resting on the ice, the salt lowers the ice's melting point, causing it to start to melt a little. As it refreezes, the ice freezes around the string. Our first attempt was a dud. You could feel that the string stick a little to the ice, but pulled right off. But it turned into an accidental experiment on states of matter - jr. scientist A was delighted to find that when he held the ice in his hand, it turned into water. For our second attempt, we realized that we needed to first wet the string. That turned out to be the key. With our salt and wet string, we were able to lift up the ice - although the effect was somewhat short-lived.

Rubber band-powered boat

We used a rubber band-powered boat to investigate potential and kinetic energy. The boat used popsicle sticks held together with hot glue for the body and tape-covered cardboard for the paddle. A rubber band attached to the boat body goes around the paddle. The boat is supposed to go by turning the paddle, storing energy in the rubber band, which is released when you let go of the paddle. Its maiden voyage went well, paddling slowly in the bathtub. Unfortunately, before we could try a stronger rubber band that might store more energy, the boat fell apart. I guess hot glue is not as waterproof as I thought. We'll have to try to make some other rubber band-powered toys.

Stomp rocket

Finally, a pressure-based rocket experiment that works! Jr. scientist A got a stomp rocket for his birthday. The kit has a Styrofoam rocket that gets launched by stomping on an air-filled container, sending air out a tube, creating enough pressure to launch the rocket sitting on the tube. We got the rocket to go high, we got the rocket to go far - a good time was had by all. We also played with the launcher itself, pushing on the air-filled container and having Jr. scientist A feel the air that came whooshing out so he could see how it all worked. Hmm, I wonder what else we can launch...

Water race

To try to show that, even though water looks the same after you dissolve salt in it, it's changed, we decided to compare the speed of diffusion for salt water and fresh water. We filled one bottle with fresh water, dyed green, and a second bottle with water with Epsom salt dissolved into it, dyed red. Then we rolled up a paper towel and put an end in each bottle. The green fresh water started climbing the paper towel. At first it looked like the red salt water was just sitting there, but we checked and the un-dyed paper towel coming from the red was wet, while the paper towel from the fresh water was only wet where it was green. Eventually the red color started moving along the towel. It looks like the salt slowed the diffusion of the color, but not the diffusion of all the water.

Making water run upstream

We decided to try to make water run upstream, so to speak, using diffusion. We filled a bottle with colored water. Then we took a long piece of paper towel, rolled it up, and used string to keep it rolled up. We put one end of the paper towel in the water-filled bottle and the other end in an empty bottle that we put on a raised platform. Nearly instantly the colored water started creeping up the paper towel. We quickly learned that a paper towel saturated with water is much heavier than a dry paper towel and we had to add supports to hold the paper towel up. Throughout the evening we watched its slow progress. We checked on it in the morning and, to our surprise, the water hadn't made it all the way to the other bottle. Instead, it stopped part-way up, leaving a dark ring of color, followed by dry paper towel. I guess diffusion will only go so far.

Mixing colors

Jr. scientist A got a science kit for his birthday that included pipettes and tablets to make colored water, so we started mixing colors together. It took some practice for him to get used to using the pipettes, but once he got it working, he was intrigued that mixing two liquids together created something that didn't look like either of the things he started with.

Vacuum in a bottle

As part of our next attempt to make stalagmites and stalactites, we tried to get our salt-water solution to slowly drip out of a container. We poked a hole in the bottom of a plastic bottle. By screwing on the top of the container, we could slow the flow of the leak - as water leaked out, there was no opening for air to go in, causing the pressure to decrease inside the bottle, creating a vacuum. Jr. scientist A loved seeing the liquid go faster or slower out the hole in the bottom as we unscrewed the cap and screwed it back on. A big hit!

Baking soda and vinegar balloon

Having previously mixed baking soda and vinegar together to make a bubbly mess, we decided to try to harness that released carbon dioxide to inflate a balloon. We poured baking soda into a bottle, added vinegar, and then quickly put a balloon over the opening of the bottle. Very quickly the balloon started to inflate, much to Jr. scientist A's delight. A fun and repeatable experiment - just a little hard to get the balloon on in time.

Stalagmites and stalactites, take 2

Our second attempt at making stalagmites and stalactites with salt crystals. This time we used a paper towel to connect the two jars filled with Epsom salt dissolved in water. The liquid did slowly travel up and across the paper towel, making the paper towel rigid, and we got some crystals forming below the paper towel, but nothing that looked like stalagmites or stalactites. We'll have to keep trying.

Cold air balloon

We tried to inflate a balloon using cold air by sticking a balloon over the opening of an empty bottle we took out of the freezer. The idea was that as the air warms up, it expands, inflating the balloon. We left the bottle and balloon out overnight to warm up the captured air and found a somewhat inflated balloon in the morning. Not a very impressive effect. Maybe we need a bigger bottle.

Floating paperclips

Our previous attempt to use surface tension to float objects found that a paperclip was too heavy. Looking around online, it seems like there might have been a flaw in our approach. By dropping the paperclip in, we might have broken the surface tension. This time, we first floated a piece of paper and dropped a dry paperclip on the paper. Then, using a pipe-cleaner, we pushed the paper under water, being careful to not touch the paperclip. The paperclip stayed floating on top of the water. I then gave Jr. scientist A a couple paperclips to drop in the water and he watched in amazement as his paperclips just dropped to the bottom while mine floated (thanks to the paper trick I used with mine). True to the physics of floating-by-surface-tension, we added a squirt of dish detergent to the water and the floating paperclip sunk like a stone... er... like a paperclip.