1. Chapter 4: The Properties of Fluids

2. 4.1 matter: anything that has mass and volume
mass: the quantity of matter that a substance or object contains
volume: the amount of space taken up by a substance or object

3. There are three familiar states (phases) of matter:
solid: has a definite volume and shape
(unless in small pieces, eg. sand)
liquid: has a definite volume, but shape depends on its container
gas: volume and shape are determined by surroundings

4. Fluids are substances that flow because some sort of force is exerted on them (eg. gravity)
both liquids and gases are fluids
how quickly a fluid flows in a given amount of time is called its flow rate

5. The kinetic molecular theory states that:
All matter is made up of very small particles (atoms and molecules) and there is empty space between particles.
Particles are constantly moving. They collide with each other and the walls of their container.
a. Particles of a solid are so tightly packed together they cannot move around freely, but can only vibrate.
b. Particles of a liquid are farther apart and can move by sliding past each other.
c. Particles of a gas are very far apart and move around quickly. 
There are forces of attraction among particles. Energy makes particles move. The more energy they have, the faster they can move and the farther apart they can get.

6. Changes of State
all matter can change from one state to another by increasing or decreasing the energy of the substance
eg. water
in solid water (ice), the particles have low energy, vibrate in a fixed position and are close together; the force of attraction between the particles is strong
as heat energy is added, the particles increase their motion and the forces of attraction become less strong; they can slide past each other so that the solid (ice) becomes a liquid (water)
as more heat energy is added, the particles move even faster and farther apart and the forces of attraction decrease further; some can break away from the surface of the liquid to become a gas (water vapour or steam)

7. the changes of state due to increasing the heat energy of a substance are:
solid → liquid: melting eg. icicles melting
liquid → gas: evaporation eg. puddles or clothes drying
solid → gas: sublimation eg. dry ice (frozen carbon dioxide)

8. The changes of state due to decreasing the heat energy of a substance are:
gas → liquid: condensation eg. water forming on the outside of a cold drink; rain
liquid → solid: solidification eg. water freezing
gas → solid: deposition (often also called sublimation) eg. frost forming on window; snowflakes

10. 4.3 viscosity: the resistance of a fluid to flowing and movement
we say a thick fluid has high viscosity, or is very viscous
we say a thin fluid has low viscosity
eg. syrup is more viscous than water since it is thicker
and therefore has more resistance to flowing
the kinetic molecular theory (KMT) says that this resistance is due to forces of attraction between particles

11. cohesion: the attractive forces among the particles of a substance
- the stronger the cohesive force, the greater the resistance of the particles flowing past one another
- different substances have different cohesive forces, so have different viscosities
adhesion: the attractive force between fluid particles and particles of another substance
- eg. water particles are attracted to glass particles, causing the meniscus to form
- eg. ketchup and syrup stick to the sides of the bottle
- eg. water will “climb” up a paper towel even though gravity pulls down

12. surface tension: the increased attraction among the particles at the surface of a fluid
- eg. water strider insects can use the
surface tension of water to stay on the surface
the units for viscosity are poise (P), but for now we will just use “high” and “low” to describe it
viscometer: an instrument that measures viscosity
- can time how long it takes a solid to fall through a column of liquid

13. Temperature and Viscosity
the viscosity of a fluid decreases as you increase its temperature and vice versa
as heat is taken away from a fluid its particles slow down and come closer together, which increases the force of attraction between the particles and so makes it harder for them to flow past each other

14. 4.5 Mass and Weight mass: the amount of matter in an object
measured in grams (g) or units derived from grams: milligrams (mg) or kilograms (kg)
stays constant throughout the universe
g = 1 kg and mg = 1 g

15. weight: a measurement of the force of gravity pulling on an object (different from mass!) - measured in newtons (N)
- multiply the mass in kg by the acceleration of gravity on Earth (9.8 m/s2)
- eg. If your mass is 50 kg, then your weight is 50 x 9.8 = 490 N

16. weight is not the same everywhere in the universe, since the force of gravity can differ from place to place
eg. on the Moon the acceleration due to gravity is 1.7 m/s2 so a 50 kg person’s weight would be 50 x 1.7 = 85 N. The force pulling down on this person is only 1/6 of that on Earth. This makes one able to jump higher and farther there

17. the mass of a solid can be measured directly by using a balance or a scale
the mass of a liquid must be measured indirectly: measure the mass of the empty container and subtract this from the mass of the container with the liquid in it

18. Volume volume: the amount of space occupied by an object
for solids, usually measured in m3 or cm3; for liquids, usually measured in L or mL
mL = 1 L and 1 mL = 1 cm3

19. the volume of a liquid can be found directly using a graduated cylinder
make sure your eyes are level with the surface of the liquid and read the volume at the bottom of the meniscus (the curve at the edges of the surface where the liquid touches the container)

20. the volume of a regular solid, such as a rectangular solid can be found directly by V = L x W x H (all in the same units)

21. the volume of a small irregular solid must be measured indirectly by displacement of water
volume of object = (volume of water + object) – (volume of water)

22. 4.7/4.9
density: the mass of a substance per unit volume of the substance
typical units are g/cm3 (solids) or g/mL (liquids)
the formula for calculating density is

23. distilled water has a density of 1
distilled water has a density of 1.00 g/mL, which means that every mL of distilled water has a mass of 1.00 g
birch wood has a density of 0.66 g/cm3 (in other words 0.66 g/mL) which means that every cubic cm of birch wood has a mass of 0.66 g
if the density of object A is less than that of object B, then A will float on top of B
eg. birch wood will float when placed in water since its density (0.66 g/cm3) is less than that of water (1.00 g/mL)
-if the density of object A is more than that of object B, then A will sink in B
eg. a piece of iron will sink in water since its density (7.87 g/cm3) is more than that of water (1.00 g/mL)

24. Questions:
A block of fir measures 10 cm by 8 cm by 3 cm. If its mass is 144 g, find the density of the wood

25. A liquid has a mass of 150 g. If its density if 0
A liquid has a mass of 150 g. If its density if 0.95 g/mL, find the volume of the liquid

26. A liquid has a volume of 1. 25 L. Its density is 1. 25 g/mL
A liquid has a volume of 1.25 L. Its density is 1.25 g/mL. Find the mass of the liquid

27. solids usually have greater densities than liquids, which usually have greater densities than gases
KMT: particles in a solid are tightly packed together therefore there are more in a given volume than there are in a liquid having the same volume
exceptions: liquid mercury is more dense than many solids; at some temperatures, liquid water is more dense than solid ice (water is densest at 4 °C)
as you increase the temperature of a substance, its density decreases eg. lava lamp

28. 4.10/4.11
when something is put into a fluid (liquid or gas), the fluid is pushed aside (displaced) to make room
the volume of fluid pushed aside is equal to the immersed volume of the object
eg. If a 10 cm3 object is immersed in water, then 10 cm3 of water is pushed aside (displaced)
eg. If half of a 10 cm3 object is immersed in water (so 5 cm3 is under water), then 5 cm3 of water is pushed aside (displaced)

29. the displaced fluid pushes back in all directions on the object
the upward force that a fluid exerts on an object is called buoyancy
Archimedes’ principle: an object immersed in a fluid will have an upwards buoyant force on it equal to the weight of the displaced fluid
in other words, the more fluid that is displaced by an object, the greater the buoyant force

31. Archimedes and the Ups and Downs of Buoyancy
Although Archimedes could weigh the crown, his problem was to find the volume of the crown. Since the design of the crown was complicated, this was indeed a problem. Archimedes realized that if he immersed the crown in water, the volume of the water displaced would be equal to the volume of the crown. Comparing the mass of the crown with the volume of the displaced water would allow him to calculate the density of the crown. If the density of the crown was less than the density of gold, Archimedes would know that the goldsmith had tried to cheat the king!
The mass of the crown is kg, and its volume is 56.7 mL. Using D = m/v calculate the density of the crown. Hint: 1 mL = 1 cm3. Remember to convert kilograms to grams before making your calculations.

32. Forces Acting on Objects in a Fluid
another force that acts on an object in a fluid is the force of gravity (its weight), which is a downward force
if the buoyant force is greater than the object’s weight (i.e. the weight of fluid being displaced by the object is greater that the weight of the object), then the object will rise until it floats

33. -means that the object is less dense than the fluid
the object will float at a level so that the buoyant force is equal to the object’s weight (enough of the object will be submerged so that it pushes a mass of fluid equal to the object’s mass)
this explains why objects with different densities will float higher or lower in water: ice cubes (D = 0.92 g/cm3) are 92% submerged while birch wood (D = 0.66 g/cm3) is 66% submerged

34. if the buoyant force is less than the object’s weight (i. e
if the buoyant force is less than the object’s weight (i.e. the weight of the object is greater than the weight of fluid that is being displaced), then the object will sink
means that the object is more dense
than the fluid

35. -ball A has positive buoyancy and will rise since buoyant force > weight
- ball B has neutral buoyancy and will remain level since buoyant force = weight
- ball C has negative buoyancy and will sink since buoyant force < weight

36. Boats and Submarines
you can make a dense object float by changing its shape so that it has more overall volume and thus less density
eg. A solid ball of aluminum foil (D = 2.7 g/cm3) will not float on water but if you mold it into a hollow shape, so that its overall volume has increased and therefore overall density (including the air held inside it) has decreased to less than 1.00 g/cm3, it will be able to float
even though steel is much denser than water (8 times as dense), steel boats are still able to float
ship engineers design the hull (body) of a ship to contain a large volume of air so that the boat’s overall density, including the hollow hull, is less than the density of water (so it floats!)

38. a submarine is able to control its overall density by taking on or pumping out water (called a ballast)
it descends if its ballast tanks are filled with water (overall density greater than seawater)
it ascends if its ballast tanks are emptied and replaced with air (overall density less than seawater)
it remains neutrally buoyant if its ballast tanks are filled with just the right amount of water and air (overall density the same as for seawater)

40. Temperature and Buoyancy
as you increase the temperature of a fluid, it becomes less dense
this means that an immersed object would displace less fluid than it would in the same fluid at a lower temperature
therefore, buoyant force decreases with an increase in temperature, i.e. objects aren’t as buoyant in warmer fluids as they are in cooler fluids