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- 1. Chapter 3 Section 2, 3 and 4 Floating and SinkingCreated by: Hamdy KarimGrade level(s): 8th gradeSubject area: Science
- 2. KS Standards and Activity Instructions:Standards/Indicators.) Use KS standards, not district standards. Include both number and standard description as well as indicator (Grades 8-9STANDARD 2: PHYSICAL SCIENCE- The student will apply process skills to develop an understanding of physical science including: properties, Solids, Liquids,. and GasesBenchmark 3: The student will investigate Floating and Sinking of different Objects?.Indicator 2: Describes, measures, and represents data on How do they calculate the density by knowing the mass and volume of an object:Activity Instructions..Slide 3- Click on the numbered list 1-4 to open questions for discussion for the class related to the floating and sinking of some objects like Pepsi cans, ships......etc.Slide 4- Continue the class discussion, click on the hidden definition of "density", and see if the new definition changes the classes answer to the first question.Slide 5- Read slide 5 to the classSlide 6- Read each blue card to the class. Have students hold up one finger if they think it is in motion, and two fingers if they dont think the situation is describing motion..Once the class is showing their answers have a student click on the box to reveal the answer.Slide 7- Introduce the vocabulary word "reference point". Have students create a list of reference points they could use while sitting on a bus.Slide 8- Click on the numbered list to open questions for class discussionSlide 9- Introduce the metric system. Pass out meter sticks for students to look at. Show them each of the measurement units identified on the stick. Give students practice. using units by completing the "Metric Inventory 2" document attachedSlide 10- Go over density formulas, emphasizing difference between constant and average speed. Practice calculating speed by completing "Bubble Gum Physics" handout.attached
- 3. Floating and Sinkingstruck an iceberg and divided intotwo. Both pieces sank to thebottom of the Atlantic Ocean. More *than a thousand people died. In e pts t of the C onc effecApril 1912, the Titanic departed Key is the ce sity * t r en wha yant fo use d r anfrom England on its first and only o u ?bu can yo wheth k in a e nvoyage. At the time, it was the How termine at or si e olargest ship a float nearly three to d t will fl cfootball fields long. the Titanic was obje id ?flualso the most technologicallyadvanced ship in existence. Its hullwas divided into compartments,and it was considered to beunsinkable. But unfortunately theship struck an iceberg and dividedinto two pieces that sunk into thebottom of Atlantic Ocean
- 4. How is it possible that huge·ships made of steel can float?easily in waterYet in a few hours the same·ship can become a sunken.wreck like the TitanicWhy does most of an·iceberg lie hidden beneath?the surface of the waterTo answer these questions,·you need to find out whatmakes an object float and.what makes an object sink
- 5. Comparing DensitiesOne reason objects float or sink is.their densityAn object that is more dense than ·the fluid in which it is immersed.sinksAn object that is less dense than ·the fluid in which it is immersed.floats to the surfaceIf the density of an object is equalto the density of the fluid in whichit is immersed, the object neitherrises nor sinks in the fluid; it floats .at a constant level
- 6. Comparing DensitiesNow you know whylead sinks: it isseveral times . denser than waterCork, which is lessdense than water,.floatsIs an ice cube moreor less dense than?water
- 7. Iceberg straight ! aheadAn ice cube floats in waterbecause the density of ice is. less than the density of water!But it’s just a little lessSo most of a floating ice cube .is below the surfaceSince an iceberg is really avery large ice cube, the partthat you see above water isonly a small fraction of the . entire icebergThis is one reason whyicebergs are so dangerous to.ships
- 8. Buoyant ForceIf you have ever picked up an objectunder water, you know that it seems.lighter in water than in airWater exerts a force called buoyant.force that acts on a submerged objectBuoyant force acts in the upwarddirection, against the force of gravity,.so it makes an object feel lighter
- 9. Weight vs. Buoyant ForceThere is always adownward force on a.submerged objectThat force is the weight. of the objectIf the weight of theobject is greater than thebuoyant force, the object What can you infer about the. will sink weight and buoyant force fromIf the weight of the ?the pictureobject is less than thebuoyant force, the objectwill begin to float
- 10. Archimedes’ PrincipleYou know that Archimedes discovered that a submergedobject displaces, or takes the place of, a volume of fluid equal. to its own volumeUsing this idea, Archimedes came up with a principle thatrelates the amount of fluid a submerged object displaces to . the buoyant force on the objectIt states that the buoyant force on an object is equal to the.weight of the fluid displaced by the objectTherefore, the more fluid an object displaces, the more.buoyant force it will haveThe more surface area an object occupies, the more water is . displacesThis is why it is easier to float in water when you are lyingdown on your back – you take up more surface area,displacing more water, therefore creating a greater buoyant.force
- 11. Floating by changing massChanging the density of an object can make it.float or sink in a given fluidEven though you cannot change the densityof an individual substance, you can changethe overall density of things that are made of.several materialsSubmarines can change their overall mass,and therefore their density to allow them to . float and sinkThey do this by filling or releasing water from .their flotation tanks
- 12. When water is pumped out of its flotation tanks,.the overall mass of the submarine decreasesSince the volume remains the same, its density.decreases when its mass decreases .So the submarine will float to the surfaceWhat do you think a submarine does in order to?sink. To dive, the submarine takes in waterIn this way, it increases its mass (and thus its!density) and sinksMost ships are also designed to alter their.overall densityThe hull (bottom part) of a ship contains a large . volume of airThis air reduces the ship’s overall mass, and.therefore its density, and helps it to float
- 13. Floating by changing volume.Another way of changing density is to change volumeIf the mass is kept the same, increasing the volume of.a substance, will decrease its densityIncreasing the surface area of a substance, will also.increase its buoyant forceThis is because the greater the volume of waterdisplaced, the greater the buoyant force (Archimedes(.PrincipleThe shape of a ship causes it to displace a greatervolume of water than a solid piece of steel of the . same mass because it has a greater surface area!The more water it displaces, the easier it will floatA ship stays afloat as long as the buoyant force is.greater than its weight
- 14. Pascal’ s PrinciplePascal discovered that pressure increasedby the same amount throughout an enclosedor confined fluid. When force is applied toa confined fluid, the change in pressuretransmitted equally to all parts. of the fluidThis relation known as Pascal’s .principle
- 15. Bernoulli’s PrincipleIt states as the speed of a moving fluidincreases, the pressure within the fluid .decreases

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