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