Overview of Lessons:
More dense sink. Less dense float.
Those six words help explain much of the Earth Science phenomena I teach during the school year. In order to understand this key idea, my students need to understand what the concepts of mass, volume, and density and how we measure these properties of matter.
To teach these properties students investigate 3 claims-one at a time:
- Objects with high mass sink.
- Objects with high volume sink.
- Objects with high density sink.
To do this I put about 10-15 items from the classroom of various volumes and mass in a bin. I make sure to freeze a big water balloon (measure the volume of water you filled the balloon with before you freeze!) and then peel off the balloon to make a huge and heavy “iceberg”. I also include a coke and diet coke can.
Other key ideas in these lessons:
1. Determining that the density of water based on our data
2. Fluids of different densities don’t mix.
Students will demonstrate their understanding of these ideas by stacking liquids based on their density calculations and the participating in the density challenge.
Before any investigating begins we review our “rule” for what makes matter, matter from the previous lesson (something along the lines of has mass, and takes up space). To begin assessing students preconceptions about mass I display a beaker, graduated cylinder, ruler, cup, scale, beam balance, etc. and ask, “Knowing what we know about mass, what tool do you think we use to measure it. Why”? (Think, Pair, Share)
Then I teach a mini-lesson on mass which include student friendly definition, how to read a triple beam and electronic balance, metric unit, and difference between mass and weight. My students create a word web for mass.
Resources for mass mini-lesson:
- Video: In this video from NASA’s Teaching From Space initiative, two astronauts aboard the International Space Station (ISS) describe mass and weight and the differences between the two. More ISS videos: https://www.youtube.com/playlist?list=PLPfak9ofGSn9vOEkIz328i4xQQq7e0kjc, Liquid Ping Pong in Space, (stress how the mass of the all the objects on the ISS has not changed, but the weight has because weight is dependent on gravity).
- Triple Beam Balance tutorial
- Mass ppt found here
After the mini-lesson, I ask students to consider this claim: Objects that are high in mass (heavy things) sink in water. They explain whether they support the claim, disagree with the claim, or not sure and discuss how we should test the claim. What evidence would support or refute the claim?
Usually it comes down to 1. Measure the mass of 10-15 objects. 2. Record answers in a spreadsheet. 3. Observe if they sink or float. 4. Record information in the spreadsheet 5. Arrange items in order of least mass to most mass and analyze the data for patterns. (There is no pattern-some high mass objects sink; some high mass objects float)
A similar lesson sequence is done for volume: mini-lesson on volume which include student friendly definition, tools to measure volume, how to read a graduated cylinder, how to calculate volume of various geometric shaped solids, hot to use the displacement method for irregular shaped objects and metric unit. My students create a word web for volume.
Resources for volume mini-lesson:
We repeat the investigation steps similar to how we investigated the mass claim. No pattern will be found and students should conclude: Some big (high volume) things sink; some big things (high volume) float.
We move onto density which most students have limited background knowledge. I, again, teach a mini-lesson on density. We don’t do a word web though until after the investigation so they can add our conclusion about density affecting how objects sink or float.
Density mini lesson resources:
- density ppt: Densitypowerpoint
- I really like how this teacher uses hands-on tools and analogies to teach the concept of density. http://blog.teachersource.com/2012/01/03/density-who-knew-they-could-be-so-dense/
- Manipulate the density pHet simulation and look for patterns: http://phet.colorado.edu/en/simulation/density I like this lab sheet that goes with it https://phet.colorado.edu/services/download-servlet?filename=%2Factivities%2F3314%2FDensity_SimActivity.pdf
- This lesson uses more Math Common Core Standards to understand that density is a relationship between mass and volume. Will try this when I teach the concept again http://www.causalpatterns.org/resources/density/density_section_2_goals3.php?continue=click+to+continue (The whole unit here: http://www.causalpatterns.org/pdfs/CausalPatternsInDensity.pdf)
Afterwards, we repeat the investigation steps similar to how we investigated the mass and volume claim but this time, when arranged from least to greatest students should notice a pattern. Ask students:
- What do all objects that sank have in common? That floated?
- Based on the data, what can we infer that the density of water is?
- What happens if an object is more dense then water? Less dense then water?
- What if it wasn’t water in the tank but another fluid? What would happen to the results? How can we test this?
Students that write up a CER (claim, evidence, reasoning) essay that sums up our investigations.
We then test this claim: An object will sink if its density is greater than the density of the fluid it is in; it will float if its density is less than the fluid it is in.
As a whole class demonstration show student 7 different fluids. Ask students how we can use these fluids to test the claim. Then calculate their densities, make hypothesis and then pour them together. Discuss the results. http://www.stevespanglerscience.com/lab/experiments/seven-layer-density-column/
Students can also explore a simple oil and water demonstration https://www.youtube.com/watch?feature=em-subs_digest&v=MFdo20GLtBs&app=desktop
These are two other investigations I’ve done in the past to engage students in understanding the concept of density and it’s relation to sinking and floating:
- The density challenge: “Modify three film canisters so that they will float, sink, or remain suspended in the middle of a tub of tap water. One canister should float (1), another should remain suspended in the middle of the tank (2), and another should sink to the bottom (3).” http://sciencespot.net/Media/myscanister.pdf or this one which is similar http://www.flinnsci.com/Documents/demoPDFs/PhysicalSci/PS10393.pdf
- Investigation about the density of salt water vs. fresh Fresh vs. Salt worksheet
Finally, we create a word web for density that includes the main ideas learned from the lesson.