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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 -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 M = mass ( G) V = volume (ml) or (cm3)
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 Mass ( g) Volume ( cm3) Density ( g/cm3) 12g 18cm3 25cm3 1.6g/cm3 35g 0.7g/cm3

15 Assignment BLM 5-5, 5-6 Pg #4 Density booklet

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

17 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.

18 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)

19 Hydrometer an instrument used to measure the density of liquids See page 154

20 Assignment BLM 5-11, 5-20, 5-21 Read pg Pg #1-7 Buoyancy booklet


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