Chapter 5: Density and Buoyancy5.1 : 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 per volume (cm 3or ml 3) than another substance (B), then it will float.

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

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)

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.

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

Assignment

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

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

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)

Example 1. A cube has a width of 2cm and

a mass of 12g. What is the density of the cube?

What else can we do with it?

Mass ( g) Volume ( cm3)

Density ( g/cm3)

12g 18cm3

25cm3 1.6g/cm3

35g 0.7g/cm3

Assignment

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

Buoyancy

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

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.

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)

Hydrometer an instrument used to measure the

density of liquids See page 154

Assignment

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