Unit B – Fluids

1. Unit B – Fluids Chapter 4 – The Properties of Fluids Chapter 5 - The Use of Fluids Chapter 6 – Fluids and Living Things

2. Key Ideas Fluid Flow is important when an object is moving through a fluid or a fluid around an object Fluids can be describe using their properties The Kinetic Molecular Theory can explain the behaviour of fluids Temperature can affect the properties of fluids Chapter 4 – The Properties of Fluids

3. 4.1 – A Close-Up Look at Fluid Flow

4. Fluids Flow • Fluids are things that flow – Gases & Liquids • Fluids flow because some sort of force is pushing or pulling them • FORCE – a push or pull that causes movement • The most common force is the force of gravity • FLOW RATE – how quickly a fluid flows in a given amount of time

5. Fluids Flow • Systems that involve movement, such as moving fluids, are said to be dynamic • Air or gas moving around solid objects is referred to as aerodynamics • Water or liquids moving around solid objects is referred to as hydrodynamics

6. Solids That Seem to Flow • Some solids can be poured (powder, sand) and can appear to flow but these are not fluids • If it can form a pile – it is not a fluid

7. The Kinetic Molecular Theory • All matter can exist in three states and can change from one state to another • Solid Liquid Gas • The Kinetic Molecular Theory is a model that helps us understand how matter can change from one state to another.

8. Kinetic Molecular Theory • The Kinetic Molecular Theory states that: • All matter is made up of very small particles (molecules and atoms) • Particles are constantly moving • Solids – particles packed so tight that they can only vibrate • Liquids- particles farther apart so they can slide past each other • Gases- particles very far apart, move quickly • There are forces of attraction among particles

9. Kinetic Molecular Theory

10. Temperature and Changes of State

11. Explaining Flow Using the Kinetic Molecular Theory 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

12. 4.2 – Fluid Flow Around Objects

13. Shape of an object determines how fluids flow around it • Laminar Flow- Flow in which a fluid travels in straight, or almost straight lines • Turbulent Flow- fluid flow characterized by irregular patterns when a fluid is unable to travel in straight lines

14. Shape of an object determines how fluids flow around it • Drag- A force (air or water resistance) that acts to slow an object moving through a fluid. • Streamlined- shaped to create laminar flow, has less air or water resistance (less drag) also called aerodynamic

15. Wind Tunnels Resistance and Aerodynamics

16. 4.3 – Viscosity: A Property of Fluids VISCOSITY- The resistance of a fluid to flowing and movement

17. Viscosity The Kinetic Molecular Theory helps us understand that resistance is due to the forces among particles COHESION – The attractive forces among the particles of the same substance The stronger the forces of attraction are, the greater the resistance of particles moving past one another

18. Viscosity • ADHESION – The attractive forces between the particles of a fluid and the particles of another substance • The reason why ketchup sticks to the sides of a bottle

19. SURFACE TENSION • In liquids, the attractive forces among the particles at the surface are greater than the attractive forces among the particles deeper in the liquid – this is called surface tension • SURFACE TENSION– The increased attraction among the particles at the surface of a liquid

20. Measuring Viscosity An Instrument that measures viscosity is called a viscometer

21. 4.5 – Measuring Matter: Mass, Weight, & Volume

22. Mass & Weight • Mass– the amount of material in an object • An object’s mass stays constant everywhere in the universe • Mass is measured in grams (g) (kilo, milli, micro) • Weight– a measurement of the force of gravity pulling on an object • An object’s weight varies depending where it is in the universe • Weight is measured in Newtons (N)

23. Mass vs. Weight

24. Volume • Volume– a measure of the amount of space an object occupies. • It is measured in cubic meters, cubic centimetres, litres, or millilitres • Meniscus– curved surface where a liquid contacts the wall of a container • Forms due to the adhesive forces between the fluid and the container

25. Measuring Volume • Measuring the Volume of a Liquid: • You can measure a small volume in a graduated cylinder • Remember to read the volume from the bottom of the meniscus at eye level

26. Measuring Volume • Calculating the Volume of a Rectangular Solid: • Volume = length x width x height • If you measure all the sides in centimetres then the volume will be in cubic centimetres (cm3) • *REMEMBER* - one cm3 = one mL

27. Measuring Volume • Calculating the Volume of an Irregular Solid: • Use technique called DISPLACEMENT • Volume of solid = (volume of water + solid) – volume of water

28. Measuring Volume Calculating the Volume of an Irregular Solid

29. DENSITY – Mass per unit volume of a substance 4.7 – Density: Another Property of Fluids

30. Using Density It is expressed as grams per cubic centimetre (g/cm3) or grams per millilitre (g/mL) Density is calculated by dividing the mass of an amount of a substance by its volume. Density= mass/volumeor D=m/V

31. Density is a Property of Fluids and Solids

32. 4.9 – Comparing Densities

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

34. What portion of an iceberg is submerged?

35. 4.10 – The Ups and Downs of Buoyancy The volume of fluid displaced is equal to the volume of the object in the fluid

36. Buoyancy • Buoyancy – The upward force that a fluid exerts on an object • Buoyancy is not the only force that acts on an object in a fluid – The force of gravity (weight) also acts on the object

37. Archimedes Principle • Archimedes Principle – the buoyant force on an object immersed in a fluid is equal to the weight of the fluid that the object displaces

38. 4.11 – How and Why Do Things Float?

39. Forces Acting on a Floating Object Positive Buoyancy- the tendency of an object to float or rise in a fluid because the object weighs less than the fluid it displaces Neutral Buoyancy- The tendency of an object to remain at a constant level in a fluid because the object weighs the same as the fluid it displaces Negative Buoyancy- the tendency of an object to sink in a fluid because the object weighs more than the fluid it displaces.

40. Forces Acting on a Floating Object

41. Buoyancy in Air 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

42. Buoyancy in Air Buoyancy in Air Buoyancy in Water

43. Plimsoll Lines

44. 4.12 – How Does Temperature Affect Viscosity and Density?

45. How Does Temperature Affect Viscosity and Density? • 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: A Special Case • Water behaves differently from other fluids when the temperature changes