Density is an awesome property of matter. Density can help identify unknown materials (circa Archimedes and the Gold crown). Differences in density determine the relative position of objects (ie. Which objects sink and which objects float). Unfortunately, students too often learn that density is just a formula. A calculation. That it’s not applicable to the real world. Sure, ships and boats are applications of density at work, but it’s hard for students to realize all the connections. Students may wonder, Yes, there are lots of air pockets and empty spaces in boats that make it less dense than water, but metal is also a very heavy dense object too.” So, what’s another way we can teach density so that students can see the connection between theory and real life? What density lab can we do?
When I first started teaching, I was told that students won’t remember what was taught, but they’ll remember what was done. Two years ago, I taught students about density by baking different types of bread in science class. And, today, my students still remember it (the bread making part of it, that is). The activity itself is meant to be a density lab with an inquiry twist, but it can be modified to be a single classroom activity – depending on class needs and time restraints. At the end of this post, I provide a checklist for my original bread density lab along with some modifications to make it go faster and easier.
Bread is a great medium to use to teach density because it is something everyone can relate to and there is a a lot of science behind baking. And, bread is also very easy to work with. Because bread can be cut into rectangular prisms or cubes, students can measure the volume and mass and calculate the density easily. And, because students get to see the air pockets in bread slices, students can easily see that less dense bread typically has more air pockets and more dense bread is more packed together. And, that’s the general idea behind density, isn’t it? Density is basically how much mass (or material) is packed into a given volume. Bread easily demonstrates this point.
Our own bake-off
In the original version of the bread density lab, students bake a regular loaf of white bread – for which I provide the recipe. Then, they cut into the bread, cutting out a nice rectangular prism for which they measure the volume and mass and calculate density. This is “control loaf”. Next, students need to take one ingredient used to bake bread and modify the amount used. Students need to make a hypothesis, for example, if more sugar is used, then the density of the bread will decrease. Then, students bake bread again using the same recipe as before with one exception. This time, they use a modified amount of whatever ingredient they decided to study. They find the density of this loaf of bread and compare to the control loaf. And, the cycle can repeat itself depending on how much time there is. In our case, the students made 3 loaves of bread (including the original). And, they loved every aspect of it (even the eating part when they took the bread outside science class).
- Have students make qualitative observations and conclusions regarding the bread. How do you know this bread is less dense or more dense? What is causing this bread to be more or less dense? Explain using CER (Claim, Evidence, Reasoning).
- Make this a cross curricular activity. I was lucky to work with one of our Home Economics teachers, who loved what I was doing and didn’t mind helping me out with the supplies and using the oven. This makes everything much, much easier. I can focus on the science component of things (ie. scientific method, observations, etc.) while the home economics teacher can focus on the hands-on piece. Also, administrators love it when departments work together to make learning more hands-on and applicable for students.
- For a one day activity, I would buy various types of bread from the grocery store (rye, whole wheat, barley, white, etc) and have students find density and compare instead of baking my own bread.
- To bake quicker and more efficiently, consider getting a bread maker. Some bread makers allow you to literally dump in ingredients, set, and forget. This is a great way to demo the bread making. Bake one loaf one day, then change one aspect and bake the next day again. It’s fast, and some bread makers can be quite inexpensive.
- Another way of doing this lab is to have students bake muffins. A muffin tin has anywhere between 6 and 12 wells Thus, students can bake 6-12 different variations of the same recipe at the same time. And, their densities can be compared right after.
Density can be an abstract idea. It doesn’t help that some students just memorize the definition and formula. But, when students see it in the ordinary, everyday things (like bread!), it makes it more concrete. More real. And, students remember if so much more. And, long after they’re graduated, hopefully, they’ll remember what a great time they had in science class too. Click on the link below to join our email list and get a copy of a simple checklist of the original bread density lab and some suggested modifications emailed to you.
Until next time, keep it REAL.