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Standard 8

Standard 8. Density and Buoyancy. All objects experience a buoyant force when immersed in a fluid. Anticipatory Set. Why do you think these two liquids weigh differently when they are the same amount?. Standard 8.8 (a-b). Students know density is mass per unit volume.

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Standard 8

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  1. Standard 8 Density and Buoyancy All objects experience a buoyant force when immersed in a fluid.

  2. Anticipatory Set Why do you think these two liquids weigh differently when they are the same amount?

  3. Standard 8.8 (a-b) • Students know density is mass per unit volume. • Students know how to calculate the density of substances (regular and irregular solids and liquids) from measurements of mass and volume.

  4. LANGUAGE OF THE DISCIPLINE • Density: the mass-to-volume ratio of a substance • Volume: is the amount of space occupied by a 3-D object • Graduated Cylinder: container used to measure volume of a liquid.

  5. Density • Which grouping is the most dense below?

  6. Density • Density is a physical property of matter • Density can be used to identify things • Example: No matter what size Aluminum is, or what shape, it will always be the same density • The ratio of mass to volume will always be the same

  7. Measuring Volume

  8. Water displacement • Example: What is the volume of the dinosaur? • V (solid)= V (water & solid) – V (water) 5.6-4.8 = 0.8

  9. Calculating Density

  10. Check for Understanding • If you want to know the density and only know the mass what else do you need to find? • volume • What method should you use to find out the volume of an irregular solid? • Water displacement • How do you figure out the volume of a regular solid? • Length x width x height

  11. Practice & HW • Guided Practice: • Read through Guided instruction on page 63-64 and highlight important information • Complete questions 1-4 on page 64 • Raise hand for a stamp • Independent Practice: • Complete questions 1-4 on page 65 • HW: • Worksheet

  12. Anticipatory Set Why do some objects sink and some float?

  13. Standard 8.8 (c-d) • Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced. • Students know how to predict whether an object will float or sink.

  14. LANGUAGE OF THE DISCIPLINE • Buoyant force: the upward force acting on a submerged object • Hydrometer: tube-like instrument used to determine density of liquid compared to water • Archimedes principal: a substance in a fluid is help up by a force equal to the weight of the displaced fluid • Naturally buoyant: an object that will not sink

  15. Buoyant Force • is equal to the weight of the volume of fluid displaced by object. • So BIGGER VOLUME= BIGGER BUOYANT FORCE • Is measured in NEWTONS (since it is a force) • This is why you feel lighter in water

  16. Buoyant Force • Buoyant force occurs in fluids… • FLUIDS CAN BE GASES OR LIQUIDS • Example: Helium balloons rise because there is a greater buoyant force on it.

  17. Archimedes’ principal Pushed up by a force equal to weight of water displaced

  18. Sink or Float • Sinking and floating all has to do with density and buoyant force • Naturally buoyant objects will not sink • This is why oil floats on water- it is less dense!

  19. Sink or Float • EXCEPTION: sometimes very dense objects can float. • Example: Steel Boats • They can float because of they way they are shaped so they do not displace as much water. • Hydrometer • It will sink deeper in LESS dense liquid • Float higher in MORE dense liquid

  20. Check for Understanding Page 69- Questions 2-5 Answers: • The plate would sink • The weight of the rock is greater than the weight of the water displaced, so the rock will sink • The distance it sinks in hydrometer indicated the density. The lower it sinks the less dense the liquid • A beach ball on top of water (since the beach ball is full of a fluid- AIR)

  21. Practice & HW • Guided Practice: • Read through Guided instruction on page 67-69 and highlight important information • Complete the questions 6-8 on page 70 • Raise hand for a stamp • Independent Practice: • Complete questions 1-4 on page 71 • HW: • worksheet.

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