I’m always looking for something new to do with my G3 scientists, and I’ve been itching to try out some sort of density-themed program for a while now. I finally decided to just go for it, and I’m so glad I did. My crew LOVED both the density tower demonstration as well as the take-home lava lamps. We also tried a third experiment called “Light Ice, Heavy Water” – but more on that one below.
First, what exactly is “density”? As described by Andrew Zimmerman Jones on about.com’s education portal:
A material’s density is defined as its mass per unit volume. It is, essentially, a measuremement of how tightly matter is crammed together.
And who discovered the principle of density? Our beloved Greek scientist, Archimedes, who is famous for the story of how he discovered the principles of both density and buoyancy…in his bathtub, then running through the streets naked screaming “Eureka!” at the top of his lungs :)
The inspiration for this demonstration came from our dear friend Steve Spangler. The density tower does require some pricier grocery items if you really want to impress the room with as many layers as possible, but all of the items are pretty common. So if you don’t have the budget for the supplies, I suspect you can convince some friends, family, and/or co-workers to donate some supplies (like I did!).
- Tall, narrow, clear container (500 mL or 1000 mL graduated cylinders are perfect); I actually ordered this set of cylinders from the Steve Spangler store – an investment I know I’ll make use of in the future, and overall not that big of an expense
- Turkey baster (pretty crucial in creating your density tower)
- 100 mL (1.5-3.5 oz) lamp oil (this was the trickiest item to find – I ended up purchasing red lamp oil on Amazon.com)
- 100 mL rubbing alcohol (I used 70%)
- 100 mL vegetable oil
- 100 mL tap water
- 100 mL dish soap (I used Dawn dish soap because I had some left over from previous experiments)
- 100 mL whole milk
- 100 mL 100% pure maple syrup
- 100 mL corn syrup (I used light corn syrup, and it worked just fine)
- 100 mL honey
- Ping pong ball (I borrowed one from a co-worker)
- Soda bottle cap
- Plastic beads (I grabbed a handful from our craft supplies at the library)
- Grape tomato (I actually used a cherry tomato, which could explain why it landed at a different level than the experiment noted, but nothing wrong with that!)
- Board game die
- Popcorn kernels (Again, I put a call out to my co-workers and someone nicely brought me in a small handful)
- Metal nut or bolt
First, I had considered actually creating the tower in the presence of the scientists, but after watching this density tower video from Steve Spangler on youtube and seeing just how patient and careful you need to be while creating it, I decided to go another route. I actually created my full density tower the night before my program – it took about 1-1.5 hours because I really took my time with it. I used the largest of the cylinders that came with my Spangler cylinder set, and I added 100 mL of each substance. I pretty much followed Steve Spangler’s advice in the video I noted above. You can add the first couple of items just by SLOWLY pouring a small stream of the liquid into the cylinder. But then you need to start using the turkey baster to slowly add additional liquids. As Steve notes in his video, keep in mind that several of the liquids are so close in density that it is VERY easy for the liquids to actually mix. If you rush and your items mix, you can let them set for 24 hours or so, but there’s no guarantee that they will cleanly separate (at least not as much as they would have with a more careful hand used in creating the original tower).
It’s been a while since I did a classroom-style G3 program, and it worked out perfectly with the density tower demonstration. I had scientists at 5 tables, with my table up front. I disguised the density tower by putting it under a wast basket on the table, and lined up all of the items I used to create the tower along the front of my table (in no particular order). After briefly defining density, I put simple worksheets out and asked the groups at each table to see if they could guess which of the items on my table were the most and least dense. In fact, I asked them to rate the items from 1-9, with 1 being the most dense and 9 the least dense. I encouraged them to come to the front of the room and shake the bottles/containers so they could get a sense of the different viscosities (thicknesses), etc. The scientists spent a good 20 min. running back and forth, comparing notes on the various liquids. There was a lot of great deductive reasoning going into the group thought processes. For example, one scientist would say, “The Corn Syrup and the Honey both move really slow and seem much thicker than the other liquids, so they must be more dense than the others.” Or another scientist would say, “Alcohol seems to evaporate quickly when I put it on a cut, so it might be less dense than some of the other liquids.”
I then had a lot of fun revealing the true order of the liquids with the scientists, starting with the honey as the most dense, and ending with the lamp oil as the least dense. But I stressed that a lot of the liquids are actually extremely close in terms of density. For example, compare the density of some of the items used in our density column:
- Rubbing Alcohol .79
- Lamp Oil .80
- Vegetable Oil .93
- Water 1.00
- Milk 1.03
- Dawn Dish Soap 1.06
- Light Corn Syrup 1.33
- Maple Syrup 1.37
- Honey 1.42
You can see from the above list that there is a greater danger of water mixing with milk than of water mixing with honey, or with vegetable oil mixing with maple syrup.
Once our full list had been revealed, I unveiled my own density tower and encouraged the scientists to come to the front of the room for the next level of experimentation: adding objects to the tower to test their density compared to our liquids. This was probably the most fun I had all day. The G3 scientists had a blast trying to predict where our different objects would land in the density column, from the bolt to the ping pong ball and everything in-between. As you can see from the videos below, the scientists were fully engaged and invested in discovering the results of our experiment. Not all of our objects landed at the same levels as noted in Steve Spangler’s own experiment, but I simply explained to the group that our objects may be of different sizes and densities than the ones that he used.
THE LAVA LAMP EXPERIMENT
- Bottles for each scientist (I tried using recycled water bottles, but visually the lava lamps were so much better in a glass bottle. I lucked into a sale at Michael’s for some glass milk bottles with some screw caps)
- Water or Vinegar (I just used tap water to fill each bottle to the half-way point; I have read that the reaction is more dramatic with Vinegar than water, but I left that for each scientist to test at home)
- Vegetable Oil
- Liquid food coloring
- Alka-Seltzer tablets, at least one per scientist
- Paper towels for spills and oily hands
There are a lot of different versions of this experiment online, so I just used the combination of what worked best for my materials. A lot of instructions have you add the oil first, but I wanted the scientists to mix the water color first. So, I passed out the glass milk bottles to each scientist, pre-filled to about the half-way point with water (no need to be super exact). I then had them choose the color of their choice and use the food coloring to color the water. They then added enough vegetable oil to top off the bottle (with a small air pocket at the top of the bottle). We gave the bottles a chance to settle into their two layers – with the colored water on the bottom and the oil on top. I then gave everyone an Alka-Seltzer tablet. We dropped them into the bottles, quickly resealing with the cap. The Alka-Seltzer reacts with the water, forcing colored bubbles of the water up through the oil…so you get about the same affect as a real lava lamp! Once the Alka-Seltzer fully dissolves in the water, you can add another one and start the process all over again. I also find the lava lamp bottle very soothing and fun to play with in its quiet state (without the bubbling) :) My scientists were very excited to take this one home with them. We did have some accidents with the vegetable oil being poured to over-flowing, so be sure to have some paper towels on hand to help with any mess. And we actually had a few of the caps pop off the top of bottles during the bubbling phase – no doubt due to overfilling – but the reaction in the bottle was not so eruptive that we had a messy explosion (we just put the caps back on).
LIGHT ICE, HEAVY WATER EXPERIMENT – FAILURE
I had really been looking forward to trying this one out for a while, and it finally seemed like I had the right program for it. I never do an experiment with the G3 crew that I haven’t tried myself first, so of course I tested this one out. On my own, the experiment was actually a great success. However, the day of the program, I think I made a critical mistake. You first add vegetable to your cup, and then slowly squeeze some baby oil into the cup to top it off. I had pre-poured some baby oil into cups for my scientists, so on the step where we add the baby oil to the vegetable oil, I think we ended up mixing the two liquids too quickly instead of carefully keeping them in two layers. Given enough time (like 24 hours), our layers would likely have separated enough for the experiment to work. However, we clearly just did not have enough time to complete it during our program hour in the manner we did it :(
This is a really fun experiment when talking about density because you get to prove that water in its liquid form is actually MORE dense than water in its solid ice form. Kind of blows your mind when you think about it. I have a feeling I’ll try this one again some day…