Grade 8 Science unit 3: fluids & viscosity

GRADE 8 SCIENCEUNIT 3: FLUIDS &VISCOSITYChapter 8: Densitydescribes the amountof mass in a givenvolume of a substance.

DENSITYA measure of the masscontained in a givenvolume.A substance with alower density will floaton substances withhigher densities.

DENSITY AND THE PTMThe PTM states thatdifferent substanceshave different sizedparticles.The PTM also statesthat there are spacesbetween the particles.

The greater the spacesbetween the particles,the less particlestherefore the lower thedensity.Ex. Water vapour has alower density thanliquid water.

In general, gases areless dense than liquidsand liquids are lessdense than solids.

CALCULATING DENSITYYou must know the massand volume of a substancefirst.Mass: the amount of matter ina substance.Volume: the amount of spaceoccupied by the substance.

To measure the volume ofan irregular shape, youwill need to determinethe amount of water itdisplaces.

Formula:Density = Mass (m)Volume (V)mDV

SAMPLE PROBLEMS1. Find the density of a 10gmass of a substance thathas a volume of 2.0 cm³.D=mVD=10g2.0cm³D=5.0g/cm³

2. You want to put 10g of saltinto a container. What isthe volume of the containerif the salt completely fills it?V= m V= 10gD2.16g/cm³V= 4.63cm³

What is the mass of1500mL of helium?m= D x Vm= 0.0002g/mL x 1500mLm= 0.3g

Assignment: Completethe practice problemson pages 312- 314.

TEMPERATURE & DENSITYIncreasing temperature willcause the particles in asubstance in gain energy,spread out and take up lessspace.Results in decreaseddensity.

EXAMPLES/ APPLICATIONS...Hot air balloonsWarm vs. cool tire pressureWater in each of its threestates (water as a solid isless dense as the particlesmove apart as they freeze)

Drying woodSalt water is more denseSwim bladder (fish)Submarines