Framework Physics 3 An Inquiry Based Science Teaching and Learning Framework Topic/Learning Activity Investigating Density and Flotation. OP2/OP3 P3Physics Student Cohort Student Level 3rd years. Prior Knowledge Simple unit measurements of mass and volume covered in first year; also have studied gases Stimulus to Engage 1.
Before students come in to the Lab, place large clear tank/container with water on the teachers bench. Place one can each of “Coke” and “Diet Coke” into the water. Ask the students to think about what they see happening here. Get them to write down the possible reasons. Lead the students towards a direct comparison of the ingredients (see table). Hopefully someone may suggest getting the masses of the cans – it may also help to have an empty can nearby
colour (E150d), phosphoric sweeteners, colour (E150d), acid, flavourings, caffeine
Show a 1 kg or 500g bag each of sugar (sucrose) and sugar substitute (sucralose eg Splenda) – there’s a very marked visual difference in the volume of the same masses. Connect to the coke discussion. Ideas about connections between mass & volume should emerge
Other float/sink visuals when the tank of water is there:
Drop a mandarin orange in to the tank – it floats. Peel the orange and drop it in again – it sinks. Discuss the possible reasons
Try a comparison between lemons (float) and limes (sink). Discuss why
Only at the end of the discussion should the teacher introduce what scientists call density (unless students have brought it in already). Misconceptions may have to be caught here (“denser “= heavier).
The demonstrations and discussion should begin to give the students a feel for the concept of density, even if they can’t yet explain it.
The teacher needs to introduce the connection between mass and volume, and finally the formula D=M/V. Students can then busy themselves measuring the mass and volume of a variety of materials, and calculating and comparing densities. Let them use the same bank of materials to not what floats and what sinks. Build a table of results into Datalogging software and print class data tables or histograms. Science Questions Initial questions leading to the questions students will work on during the activity:
If two items have the same volume – as in those two cans – what else could we measure about them?
If two items have identical mass but look very different in size, what is the reason?
Framework Physics 3 An Inquiry Based Science Teaching and Learning Framework Learning Outcomes Content Knowledge:
consolidate knowledge of measurement in simple units (mass, volume),
P3Physics
learn formula for connecting them in density = mass/vol; learning to discriminate between use general descriptive words (size) and correct scientific terms (volume). OP2 & OP3
Process: ■
begin to understand what density means (get a better intuitive grasp of abstract concept), and its connection to flotation. Begin to be make predictions based on what is being observed. Learn to generalise from Specifics
With a great variety of measurement and calculations to be done, group cooperation skills and data processing skills will be developed
Questions during Activity Questions to drive student learning (directing them to the learning outcomes): Questions to probe understanding: ■
What should the mass of a litre of water be?
Why do substances like air, petrol, cake not have a particular density value?
Why do people refer to “densely populated” cities?
Should warming a liquid increase or decrease the density? Can you explain your answer using a diagram?
Questions to get students thinking about their own learning (metacognition): ■
How would you explain density to another student using only pictures/images/pdf/symbols?
Developing the Activity How do you stimulate students to ask even more questions/think further?
Show a Cartesian Diver in a bottle, or a Galileo thermometer – is there a connection between density and pressure? Can they explain, or make a fair guess, at what is happening in each case?
Possible supporting activities: ■
The Float / Sink challenge. Each group gets two identical pieces of modelling clay. Each group works near a sink of water or has a trough of water. The challenge is to plan how to make one piece float and one piece sink in water. Teacher allows one minute for thinking / planning / discussion (students can’t touch the clay in this time – encourages sharing of ideas and alternatives). Students then have one minute to complete their floaters and sinkers
Questions for supporting activities:
Could you float an elephant? If not why not, If so, how?
How do you make yourself float or sink when swimming?
Framework Physics 3 An Inquiry Based Science Teaching and Learning Framework Reflecting Back to Learning Outcomes:
How many of your intended outcomes were achieved?
Do any of your intended outcomes need to be revised?
P3Physics Additional Resources Interactive Density tool available at http://www.sciencejoywagon.com /explrsci/media/density.htm
For those who might take this investigation further, full nutrition information for every Coke drink available at http://www.thecoca-colacompany.com/mail/goodanswer /soft_drink_nutrition.pdf
Coke vs Diet Coke demonstration on You Tube : http://www.youtube.com/watch?v=aR0b4QRhfU0
Table of densities – there are many available http://wiki.chemeddl.org/images/pdf/3/3d/Chapter_1_page_23.jpg
How has the use of ICT enhanced the learning? Evidence of enhancement: ability to look up exact densities of various materials.
Use of Datalogging software to build student’s own data tables and histograms.
Interactive density animation gives instant feedback. Students can progress at their own pace, or teacher can use with whole class for revision
Additional Comments Density is a difficult concept even for adults. The more time spent on introduction, demonstration and questioning using real life examples the better. Formula and calculations will then make more sense (Hopefully)

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