Diving! Your submarine is descending to explore to the deep, dark depths of the ocean...how does this submarine sink and then rise from the depths again to reach daylight? Density is not only a rich physical science concept with respect to understanding matter, properties of matter and identification of matter, but it is also a perfect link between physics and chemistry. Sinking, floating and buoyancy come to play when students explore how mini-submarines float and sink.
This lesson assumes students have prior knowledge of mass (Measurement: Mass), volume (Measurement: Volume) and density (Measurement: Density) as fundamental properties of matter (Mystery Substances: Properties of Matter Investigation). Throughout this investigation, students access learning objectives related to the "Matter and Its Interactions" (MS-PS1) and the "Forces and Motion" (MS-PS2.A) Disciplinary Core Ideas. These core ideas require students to be able to analyze and interpret data on the properties of substances and understand concepts related to forces.
Density data also relates to Common Core Mathematics Standards in the Ratios and Proportional Relationships and Measurement and Data domains. As an understanding of density develops, students are better able to understand proportional relationships, which provide information about the magnitude of properties and processes and recognize that scientific relationships can be represented through the use of algebraic expressions and equations (CCC). While students conduct their investigations, they produce data to serve as the basis for evidence that meet the goals of the investigation (SP3), apply mathematical concepts and processes (SP5), engage in investigation to collect, analyze and interpret data (SP4) and construct written arguments supported by empirical evidence and scientific reasoning (SP7). The arguments practice connects to Common Core Language Arts Standards when they write conclusion arguments in Part 2 of the lesson.
The Dunking for Density Investigation series of lessons is a scientific inquiry investigation taught over the span of several days. To help manage the magnitude of this activity, you will find the project split into 2 parts.
In order to ENGAGE students in this lesson, students view the following catchy video of submarines:
Following the video, students complete the "K" (Know) and "W" "Want to Know" sections of a "K-W-L" chart for the topic of submarines. For more explanation of the K-W-L strategy, review this section's reflection: K-W-L Charts: What Students Know, Want to Know, Learn. Students share what they know and want to know with the class. A common response that pops up, is:
How do submarines dive and resurface?
When this question surfaces (ha ha), ask students this probing question:
What do diving (sinking) and resurfacing (floating) have to do with density?
Show students a photo like this one to help students visualize what sinking and floating look like and to introduce vocabulary:
From this diagram, students recognize that diving submarines are sinking, cruising submarines are suspended in water and surfacing submarines are floating. Students usually know what float and sink mean, but front-loading the word "suspend" will help students understand the investigation procedure. Have students share what they think the connection between sinking/floating and density.
This is a critical point in the discussion since floating and sinking are paired with many alternate conceptions: heaviness, mass, weight, volume, surface area and shape are common factors that students suggest. There are several strategies for handling these ideas:
1) Explore student ideas by testing different ideas using demonstrations: Density Demonstration Notes
2) Use the strategy "ignore the wrong answers for now" or "refocus on what is right". If students start playing the "what if" game, the chances of getting embroiled in a very interesting and very confusing discussion are high. Instead, focus the discussion on the right ideas.
3) Pre-teach the idea of sinking and floating with respect to density using some ideas like these warm ups: Density Concept Warm Ups.
When discussion narrows to: objects denser than water sink, objects less dense than water float and objects that have the same density of water suspend, introduce them to the lab in order to EXPLORE!
The EXPLORE stage of the lesson is to get students involved in the topic so that they start to build their own understanding. To help students explore in groups, students add to their K-W-L Charts after reading two texts:
2) Background text on Density and Buoyancy. I used a textbook, but the online resource Science Primer Buoyancy works as well.
These texts serve to activate prior knowledge and provide students with additional background information regarding submarines, floating, sinking, density and buoyancy. After students addend their K-W-L Charts, they start to plan their investigation using the Dunking for Density Experimental Design Plan (less-structured inquiry) or Dunking for Density Investigation (more-structured inquiry) in order to develop the question:
How does mass affect the density and buoyancy of a mini-submarine?
This is a structured inquiry lab in which students complete some sections of the plan while other sections are provided. The design plan can be modified to include more or less structure depending on the level of your students. At this point in the year, my students have designed several experiments, so minimal instruction or guidance during the process is required. However, due to the nature of this investigation, I've found that students benefit from coaching in the following areas:
1) Understanding of the purposed of the investigation.
2) Reading of the procedure carefully.
3) Using the procedure to extract the variables.
4) Checking the "Background Research" section to check for preliminary understanding.
5) Completion of the hypothesis to include complete predictions and reasoning.
I review student work and check for understanding of the procedure prior to progressing on to testing the submarines. An example of accurate and complete student work can be seen here: Dunking for Density Investigation Student Work. Once students have completed the experimental design plan, they are ready to conduct the investigation and collect data. For footage of students testing their submarines, view:
Teacher Note: As always, safety should be stressed during this investigation. This investigation is fun and students are very enthusiastic when trying to solve the problem of the suspending canister. The investigation uses liquids, glassware and small objects, which require goggles, limited movement and care when transferring liquids. Splashing and using pipettes as squirt guns are also enticing options for unsafe laboratory behavior. In addition to safety, it may be helpful to review with students how to calculate density (Calculating Density Video) and/or find the volume of oddly-shaped objects.
Continue on to Part 2, which includes the EXPLAIN/EXTEND and EVALUATE components of the lesson; Time: 2-3 50-minute lessons or equivalent block periods.