Primary students can simply measure the change in mass. Elementary students can look at volume and mass. Middle school kids can include density. High school kids can factor in index of refraction. After all the gummy looks much smaller when it is under water. Students are always pleasantly surprised to take them out of the water and see how much bigger they rally are.

Density is the ratio of mass and volume. In science class we use the metric system. We measure mass in grams (g) and volume in milliliters (mL). 1 mL is the same as 1 cm^{3}. It’s a measurement of how crowded something is. Greater crowding means greater density. In scientific terms we divide mass by volume to get density.

Gummy bears are inexpensive and readily available. They expand a lot in water. My students measure mass and volume of several gummy bears before they are put into water.

Some measure volume by measuring length, width and height and multiplying. That’s not accurate because a gummy bear has an irregular shape. It’s better to measure by displacement. From this they calculate density.

I have a several small portable Ohaus balances. I use Model PS 121 and while it is no longer available on the Ohaus website several other retailer sell them. Prices range between $25 and $50.

So the density of the clear gummy before the soaking is 2.6 g/2 mL = 1.3 g/mL.

They wait 24 hours and measure the mass and volume again.

The density after soaking in water for 24 hours is 9.5 g/8.0 mL = 1.2 g/mL

My students then compare the two densities.

Their challenge is two-fold. First they need to test all of the different color gummy bears to determine which gains the most in density over 24 hours.

Second, using only one color gummy bear they test various liquids. Their challenge is to determine which liquid causes the density of the gummy bear to increase the most over a 24-hour period.

*The gummy bears don’t change density before and after soaking if they are soaking in water. If they are soaking in a liquid with a density greater than about 1.2 g/mL, the density of the gummy bear will increase. The farther the liquid’s density is from 1.2 g/mL the more the gummy’s density will change It’s interesting because when we used maple syrup the gummy initially floated on top of the syrup. Throughout the day, the bear sunk deeper into the syrup probably because its density increased.*

*As for the color, it doesn’t seem to matter. In fact if yo put two gummy bears of the same color in the same cup of water for the same amount of time, sometimes the increase in mass and/or volume is not identical. It certainly make the kids think.*

What do you think happened when the bear was soaked in a liquid with a density of less than 1.2 g/mL? I’ll let you and your students figure that one out.

When my students are sure they know all about gummy bears and density I give them the mystery liquid. It’s safe to handle but we don’t know what will happen to the gummy bear when it is soaked overnight in this liquid. I encourage them to determine the density of the mystery liquid. It’s salt water and it makes the gummy bear shrink. They are really surprised when they see that!

Although the focus of this lab was density, the students got the chance to practice a lot more.

- Finding the mass of an object
- Finding the volume of an object
- Finding the volume of an irregularly shaped object (volume by displacement)
- Creating a data table (You can find my data table and graphing requirements at https://www.youtube.com/watch?v=5l672EzJ2KQ)
- Scientific method
- identifying variables
- controlling variables
- hypothesizing
- concluding
- asking more questions

I’ve got tons of ideas for other gummy bears lessons. Here are some that I need to develop.

- gummy bear genetics
- survival of the fittest gummy bears
- physical/chemical properties
- gummy melting point
- color mixing

Post a comment about what you do with gummy bears and density.

]]>

The kids can collect and save raindrops too. We don’t get much rain here in Arizona, but when we do it’s a downpour (and major event). To catch raindrops:

1. cover a cookie sheet with a layer of flour

2. Hold the pan in your hands, put it out in the rain and take it back in quickly. You want some raindrops to fall on the pan, but not so many that you turn the flour into paste.

3. Bake the pan in an oven (250 degrees for about 30 minutes). Make sure you don’t use a forced air or convection oven (which will make particles of the flour fly around the oven and could start a fire).

4. When the cookie sheet cools, put the flour through a strainer. The strainer will collect little pebble-like raindrops. Most should be relatively spherical and hard, like little rocks.

This is an amazingly fun and simple thing to do on a rainy day. The raindrops do not keep their shapes but the relative sizes are interesting. It’s fun to catch raindrops in a drizzle and compare them to a downpour.

]]>

The easiest way that I have found to teach students the concept of density is to talk about how crowded a place it. Identify a section of your classroom. As 1 student to stand in this area. Ask if it is crowded. Then add a second child, again asking the students if it is crowded. Double the number of student until you either run out of space or students. At some point the students will agree that the space is crowded.

We discuss how “crowded” a Snickers (R) bar is. Is it more “crowded” than a 3 Musketeers bar? As scientists we use the work dense instead of crowded. We can test how dense something is by seeing if it is more dense than water. If it is less dense than water it will float on water. If it is more dense than water will sink. And if the density is the same as water it will flink — which is hovering.

This is a science experiment the kids will want to try again and again. Now is the perfect time to introduce the concept of variables. Is it important that both candy bars are the same size? (No.) Is it important that both candy bars are unwrapped? Yes.

More on this later. For now, I’m going to eat a Kit Kat then go to bed. See you tomorrow.

]]>