Matter Rotations

This week we reviewed mass, volume, and density, and also began discussing the idea of conductors of heat. (We'll talk more about conductors when we get to circuits.) The students went through rotations covering each topic.
Rotation #1 was a can of Coke and a can of Diet Coke, and the students placed them in a tub of water to measure distance each sank. The regular coke sank to the bottom, while the Diet Coke did not. This lead to a discussion about the mass of sugar versus the mass of artificial sweetener, and their relative densities. I brought in a sample of each so that the students could feel the difference in mass. It a BIG difference!
Rotation #2 included a wooden spoon, a plastic spoon, a rubber spoon, and a metal spoon. The students predicted which spoon(s) would be good conductors of heat, then we put the spoons in hot water for 1 minute. We took the spoons out and timed how long it took for a small piece of butter to begin melting when placed on the spoon. We quickly noticed the metal was by far the best conductor.
Rotation #3 was about predicting and measuring the volumes of different liquids.
Rotation #4 included measuring the mass of many different objects using a triple beam balance.

Density Tubes

Beginning the density tube

We're discussing density in science, so to explore it a bit, we used three different solutions and determined their relative density. Before class I prepared three solutions. Solution #1 was 400mL of water and 10 drops of blue food coloring. Solution #2 was 400 mL of water, 10 drops of red food coloring, and 3 tablespoons of salt. Solution #3 was 400 mL of water, 10 drops of green food coloring, and 6 tablespoons of salt. The kids did not know the properties of the liquids. Their only instructions were to build the density tube, and add the liquids in a way that the layers stayed separate. All the kids began in different orders, and they all had a mix of liquids! After lots of trial-and-error, all the groups were able to get their liquids into the correct order. I discussed with each group individually why the liquids had to be ordered in this way. We discussed density, which liquid must be our most dense, and which liquid must be our least dense. We also related the density of the red liquid to the other liquids.

A completed density tube

Measuring, Comparing, and Contrasting Matter

When practicing our ability to measure, compare, and contrast objects, we began by observing a group of objects and listing out their physical properties. Physical properties are simply the observable characteristics of an object. Then the students tested to see if each object was magnetic or not. After we recorded our results, we thought about characteristics that might make an object magnetic, and if those characteristics ALWAYS make an object magnetic. For example, is an object magnetic simply because it feels like it is made of metal? 

Next we moved to comparing matter based on volume, density, and states of matter. The students were given 6 vials containing mystery liquids (water, sand, cotton, baby oil, salt water, and air.) They found the mass of each vial in grams, then they found the volume of each container by measuring the water displacement after the vial was submerged in 200mL of water. Because all of our vials were the same, the vials should all have the same volume. Finally, the students put all six vials into a bucket of water to determine if they sink, float, or stay in the middle. What they found was that the vial of water floated in the middle. This led to a discussion of why. After lots of talking back and forth, the kids finally came to the conclusion that it was because the water in the vial has the same density as the water in which we put it. The sand and salt water sank because they are more dense than the water. The cotton, baby oil, and air floated on top because they are less dense than the water.

Our final discussion was led by these two questions: Does the state of matter affect whether an object sinks or floats? No, because we had solids that both sink and float and liquids that both sink and float. Does the mass affect whether an object sinks or floats? Yes, the higher masses sink, while the lower masses float.

Measuring Water Displacement

Density Test

 

More Density

View of our jars from the top

A fuzzy side view of our jars.

As we continued our exploration of density, we began another investigation using three jars of unknown liquids. The kids didn't know the contents of the jars until after the investigation was completed. Jar #1 contained 60 mL of dish soap (blue liquid). Jar #2 contained 60 mL of baby oil. Jar #3 was nothing but air, which is why I covered it in foil. I didn't want to spoil the surprise. Some kids knew right away there was nothing in it, but some were convinced I had put something in there! The groups all measured the mass of each jar using the triple beam balance. Then they added the jars to the tub of water to observe which was the most dense/least dense. All groups came to the conclusion the blue liquid had the most mass and was the and most dense, while the foil-covered jar had the least amount of mass and was the least dense.

We then discussed why it was so important both the liquids have the same volume. If the volumes are different, we wouldn't know if the blue liquid was, in fact, more dense, or if there was just more liquid in the jar.