Class IX Physics Chapter: Gravitation Activity To build and test ‘sea vessels’ Introduction - You and your friends will explore how salt water affects the way objects float or sink. You people will use this knowledge – together with the understanding of technology – to design, build and test two ‘sea vessels’. BACKGROUND INFORMATION In this activity, you have to make your own seawater by adding salt to water. On average, seawater contains around 35 grams of salt for every kilogram of water. Seawater is denser than fresh water due to its salt content. The more salt it contains, the denser it is. STUDENT ACTIVITY You will need: • Tap water • salt • paper towel • test objects: pieces of wood, plastic containers, rocks, etc • weighted objects: coins, washers, bolts, marbles, etc • materials to build vessels: different types of plastic, ice cream sticks, wire, plastic bottles, straws, etc • construction tools: scissors, glue, hot glue gun, different types of tape, etc • large plastic tank or tub to test sea vessels • scales Per group large deep plastic bowl measuring cup ice cream container ruler scrap paper tablespoon What to do: Float or sink tests 1. Put your friends (fellow students) into small groups. Tell each group to fill their plastic bowls with water. 2. Ask each group to choose five varied objects to test. Have them record the objects and their predictions on a notebook. 3. Place each object in their bowl and record what happens. 4. Add around two tablespoons of salt for every litre of water to change their freshwater into ‘seawater’. 5. Repeat steps 2 and 3 with salt water and record the predictions and results in the first table (provided below). 6. Empty the bowls into the large plastic tub. Use paper towel to wipe away excess salt before filling the bowl with tap water again.
7. Place the ice cream container into the bowl and use a ruler to measure how much is floating above the water line. Record the result in the second table. 8. Add one cup, two cups then four cups of water to the container, measuring and recording the height of the container above the water line after each addition. 9. Remove the water from the ice cream container before adding salt to the bowl (as for the first test). Repeat steps 7 and 8. When finished, pour the salt water into the large tub. 10. Share the findings with the other groups. Discuss the factors that influence how a material floats or sinks. Record the explanation on the notebook.
Rubric for Evaluation Areas of assessment
Inquisitiveness
Weightage assigned to each area of assessment 10%
Observational skill
10%
Thinking skill (logical, rationale)
15%
Analytical
10%
Marks (%) allocated
Application of knowledge Comprehension & understanding (vivavoce)
15% 10%
Computing skills
10%
Drawing conclusions
10%
Experimental Skills
10%