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Chapter 5: Density and Buoyancy

Chapter 5: Density and Buoyancy. 5.1 : Density and the Particle theory of matter. . What weighs more, a kilogram of feathers or a Kilogram of rocks? . How many grade 8s can fit into our square?. Density . If a substance (A) has fewer particles

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Chapter 5: Density and Buoyancy

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  1. Chapter 5: Density and Buoyancy 5.1 : Density and the Particle theory of matter.

  2. What weighs more, a kilogram of feathers or a Kilogram of rocks?

  3. How many grade 8s can fit into our square?

  4. Density • If a substance (A) has fewer particles per volume (cm 3or ml 3) than another substance (B), then it will float.

  5. If a substance with more particles per volume(B) is placed on another substances with fewer particles per volume(A), it will sink.

  6. Density for a pure substance can only change if there is a change of state. • In a pure substance, the solid form is more dense than the liquid form, which is more dense than the gas (in most cases)

  7. The exception… • Water is an exception: Ice (solid) floats on water (liquid). Ice is less dense than water because of the position of the molecules when frozen.

  8. Mass vs. Weight • Mass = the amount of matter in a substance (measured in grams, g). • Weight = The force of gravity exerted on a mass (measured in Newtons, N). • Volume = the amount of space occupied by a substance. ---> in mL for liquid ---> in cm3 for solid

  9. Assignment • -Read p. 130-136 • -Do questions p. 136 #1-4 • -Read Lab 5-A p. 138-139 • -need graph paper next class

  10. Density • All matter is made up of particles ( atoms). • All atoms have mass. Some matter has more massive atoms than others. • The more massive the atoms the greater the mass. • Matter takes up space = Volume • More atoms in a certain volume mean more mass in that volume. • The mass of a given volume of matter is called Density

  11. How do you figure density? It is easy. Use this simple formula. D = density ( g/ml) or (g/cm3) M = mass ( G) V = volume (ml) or (cm3)

  12. Example • 1. A cube has a width of 2cm and a mass of 12g. What is the density of the cube?

  13. What else can we do with it?

  14. Assignment • BLM 5-5, 5-6 • Pg. 143 #4 • Density booklet

  15. Buoyancy • Buoyancy - the upward force on an object submerged in or floating on a fluid. Units = newtons (N)

  16. Average Density - the total mass of an object divided by the total volume of an object.Ex. Ships, life jackets • Neutral Buoyancy - the amount of force pulling down on an object immersed in a fluid (gravity) equals the amount of force pushing up (buoyancy). • Diagram : page 151 Sinking, Rising, Floating.

  17. Archimedes Principle: The buoyancy force acting on an object equals the weight (force of gravity) of the fluid displaced by the object. • The buoyancy force of a liquid is dependent on its density of the liquid. (direct relation)

  18. Hydrometer • an instrument used to measure the density of liquids • See page 154

  19. Assignment • BLM 5-11, 5-20, 5-21 • Read pg. 144-158 • Pg. 158 #1-7 • Buoyancy booklet

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