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 Forces of attraction between particles are strong when they are close together  Particles cannot flow in a solid b/c the force of attraction between them is too strong  Liquids and gases can flow because the molecules have enough energy to break the forces of attraction between the molecules 11

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Resistance and Aerodynamics 15

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Comparing Densities – Things to Remember 33  Each pure substance has its own characteristic density  Solids have greater densities (usually) than liquids, and liquids have greater densities than gases

What portion of an iceberg is submerged? 34

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 Buoyancy acts on objects immersed in a gas the same way it acts on objects immersed in gas – however there is ONE big difference between them  Density – the density of air is about 1/800 of that of water  You must displace a much greater volume of air to “float” in it 41

Buoyancy in WaterBuoyancy in Air 42

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45  Fluids run more easily when they are warm  Viscosity, density and buoyancy all change with changes in temperature  What happens when a fluid is cooled? How would this affect density if we know that d=m/v

46  Water behaves differently from other fluids when the temperature changes