Numerous reports suggest an increase in white shark encounters* in the United States in recent years and the public is worried.
*Encounters include sightings and census estimates, as well as physical interactions between humans and sharks.
Develop and use a model to explain the effect of object distortion at the surface of water due to refraction of light at the surface.
Researchers above water have a hard time estimating the precise position and size of a white shark under the water.
Click here for NGSS, CCSS (ELA), and California ELD standards.
In the previous series of lessons, students have explored various components of tracking devices including magnetic fields, use of waves, and digitized signals.
It is in this lesson that students build understanding of the Performance Expectation for MS-PS4-2 by understanding that light (the same wave type as radio waves) does not change direction if the light hits perpendicular to the interface, and that it does change direction if the light hits at an angle. This is done through the context of scientists being challenged in estimating the precise position of a white shark when attempting to attach a tag. Light changes speeds when it transitions between mediums (in this case, from air to water), distorting the perception of where the shark is located. Students mimic this using a skewer and a gummy candy in a bowl of water. Students discover that when light hits the water at an angle other than 90 degrees, it looks “bent” due to the change in speed therefore making it difficult to correctly perceive the position of a white shark’s location in the water. Students move on to more experimentation using lasers and objects of different densities and use patterns to identify cause and effect relationships that inform the development and modification of a model, based on evidence, to match what happens when a variable or component of a system is changed. Students apply this information to understand how aerial surveys of white sharks misreport shark size because light distorts our perception of objects.
In the next lesson, students will begin to understand one of the biggest revelations since tracking technology has been used to study white sharks–the tremendous impact humans have had on their population.
Throughout the lesson, a flag () denotes formative assessment opportunities where you may change instruction in response to students’ level of understanding and making sense of phenomena.
Part I | 45 minutes | Engage |
Part II | 45 minutes | Explore |
Part III | 45 minutes | Explain |
Develop a model of the effect of how light behaves when entering a new medium at an angle.
The method that students saw in Lesson 8.6: Tags and Waves–using a gill net to isolate a YOY white shark, about 4 feet, to place in a temporary hold for tagging–took place off Southern California, where YOY and Juvenile white sharks are common. Students may recall how two adults struggled to capture the young shark. The location of the 15-foot adult white shark tagged in this video was Año Nuevo, central California, an area frequented by adult white sharks (and a well known elephant seal colony).
Students have studied light throughout elementary school, beginning in first grade, but may need a few reminders about what they learned about light and how they might represent light in a model. If your students have not had this experience, consider allowing some time for them to plan and conduct a brief investigation of how they see objects and how light allows for objects to be seen.
The larger the bowl and the smaller the candy, the more dramatic the effect of not being able to “spear the fish” is. Spearing the fish from directly above is typically the angle that students think would be the easiest, and they are correct, but you can have a discussion about the practicality of being able to get directly above the fish, or white shark, in the real world.
For students struggling with the modeling process, suggest that they add a story of what is happening to accompany the work they are able to do (like a narrative). If able, encourage them to use this story to inspire ideas of things they can add to the model and vice versa.
Analyze, interpret, and predict the effect of changing the incident angle as it transitions between mediums.
While using glass and/or acrylic is an easy and clean medium for the students to investigate, the gelatin has novelty but is messy. If time allows and all three materials can be obtained, it can be beneficial for the students to explore and do the same sequencing with each material. This can open up deep conversations about the densities of the materials and how those densities change the angle of the refracted light because of the more dramatic changes in speed. The assessment boundary for 8th grade is for a qualitative understanding of how the light interacts with different mediums. While students are being asked to measure angles (quantitative data), this is only for comparison purposes and they are not being asked to use these in equations. Additionally, laser safety should be explained to students before lasers are distributed. The lasers should either be pointed down at the ground or through the material. They should never be pointed at another person and not turned on until they are used in the investigation. Avoid shining lasers at faces. Students can avoid this by not putting faces in the path of a laser and by placing paper behind an object that a laser is pointing at.
Refine the model of the effect of changing the incident angle as it transitions between mediums.
Have students discuss their answers and then share out with the class.
Consider allowing students who need literacy support to work in pairs; later you can make a copy of the work completed for the other student to add to their Science Notebook. Alternatively, allow students to do this work in their native language.
Expected student responses include the following:
Students in 4th grade explore the idea that an object can be seen when light is reflected from it and travels to their eyes. (4-PS4-2 Develop a model to describe that light reflecting from objects and entering the eye allows objects to be seen. [Assessment Boundary: Assessment does not include knowledge of specific colors reflected and seen, the cellular mechanisms of vision, or how the retina works.]) What is new for them to think about in this middle school context is the idea that the type of material that light passes through will change how it moves. Students should be familiar with the idea of density as variations in temperature and salinity can cause a difference in density from 6th grade (ESS2.C) and density is a property of matter from 7th grade (PS1.A). In this lesson, students can discuss density (higher density = molecules are more compact) as something that can influence the speed of light, and therefore, the “bending” of light at the transition of the two densities, but quantification of density is not required.
We perceive objects, like white sharks swimming in the water, as being larger because as light reflects back to your eye from the shark (going from water/more dense, to air/less dense), it bends away from the normal line. (For example, when the laser goes from the acrylic block/ gelatin to the air, the angle that the light exits back into the air is greater than the angle that it enters it. Our eyes could perceive that as making the object appear larger.) So in the case of the white shark, in real life, a larger angle of exit makes a smaller shark appear larger.
Differentiation suggestion: Instead of showing students 8.8.R1: Tweet from the CSULB Shark Lab and discussing the implications of using a target for size comparisons, this section could also be used to challenge students, especially those who are more motivated or engaged, to come up with their own way to determine an accurate length of a white shark before introducing them to the solution that others came up with. Once students have determined a solution, they could compare the two to determine which idea would provide the most accurate estimation of length and what the limitation of each solution might be to helping the public be aware of the size of sharks in the water.
By seating students in groups (groups of 4 work well) and encouraging regular conversation, students have time to interact more with content and naturally help those that need more support. Use of 8.1.H2: Scientist Communication Survival Kit (from Lesson 8.1: Shark Encounters) helps with making sure that students who don’t feel comfortable sharing (often because of language, literacy level, uncertainty of content knowledge, etc.) are prompted to do so in a supportive way.
Use of a sense-making Science Notebook supports student language development, conceptual development, and metacognition. Students should be prompted to use their Science Notebook for
By writing about topics in their Science Notebook BEFORE discussing, second language learners and low language students can gain confidence and organize their thoughts before speaking in front of a group. Also, sharing ideas in a small group throughout the rest of the lesson lowers the affective filter of low language students. Having students work in teacher-selected partnerships or groups allows you to match students in a way that both are being supported. Advanced students have the opportunity to explore additional questions that arise.
Consider providing sentence frames for low literacy and second language learners. The use of graphic organizers can help struggling students manage Science Notebook work.
When showing a short video, it’s often helpful to students to watch the video once to get a sense of the purpose. Showing the video a second (and sometimes a third time) allows students to focus on important details that can be recorded in their Science Notebook and discussed.
Beck, K. (2020, April 20). Light at a perpendicular interface. Retrieved from https://www.youtube.com/watch?v=09AQL10bZr4&feature=youtu.be
Beck, K. (2020, April 20). Light at an angled interface. Retrieved from https://www.youtube.com/watch?v=MX6PQF1knxQ&feature=youtu.be
Discovery News (2008, July 17). Shark Week–Shark Tagging Explained. Retrieved from https://www.youtube.com/watch?v=0eye27apFp4
Lowe, C. [CSULBSharkLab]. (2017, June 3). Shark Lab volunteers make shark target for testing size estimation using drones. #smallerthanitlooks [Tweet]. Retrieved from https://twitter.com/CSULBsharklab/status/871070923213819906
Orange County Sheriff’s Department (2017, May 10). San Clemente Sharks May 10, 2017. Retrieved from https://www.youtube.com/watch?v=oM-Qg_Wy6c8