Science Review: Fluids
Terms to know: (You’ll be given six and asked to define any five of them.)
fluid
viscosity
density
mass
volume
buoyancy
pressure
hydraulic machine
pneumatic machine
piston
Concepts to Know
1. Understand the concept of viscosity: the “thickness” of a fluid.
Sample Questions:
- Name some substances with a high viscosity and some with a low viscosity.
- If a fluid had a high flow rate, would its viscosity be high or low?
- Will heating a liquid make it more or less viscous?
- Name at least two ways to increase a fluid’s viscosity and two ways to decrease it.
2. Understand the concept of density.
Sample Questions: (You may need to use table 5.1 on p. 141; this table will be
provided on the test.)
- Which is denser, sugar or salt?
- If a chunk of oak wood were placed in a beaker of glycerol, would the oak float or
sink?
- If a chunk of iron were placed in a beaker of liquid mercury, would the iron float
or sink?
- Would a chunk of gold float or sink in liquid mercury?
- Which would be heavier: a teaspoon of water or a teaspoon of machine oil?
- When ice is dropped into a glass of water, does it float or sink? What does this
say about the density of ice as compared to the density of water?
3. Know the formula D = m/v and be able to use it to solve problems relating to the
density of an object.
Sample Questions: (You may need to use table 5.1 on p. 141)
a) An object weighs 140 grams and has a volume of 200 mL. What is its density?
Use table 5.1 on p. 141 to determine what substance the object is made of.
b) 500 mL of a liquid weighs 515 grams. What is its density? What is the liquid?
c) Ethyl alcohol has a density of 0.79 g/mL. How much would you expect 25 mL to
weigh?
d) 1.5 kg of a metal takes up 77.6 mL of space. What is its density? What is the
metal? (Remember to change kg to g first)
e) A chunk of nickel weighs 2.225 kg. What volume would you expect it to take up?
Answers to part 3: a) 0.7 g/mL, oak
b) 1.03 g/mL, seawater
c) 19.75 g
d) 19.32 g/mL, gold
e) 250 mL
4. Understand how an object’s density relates to its buoyancy.
Sample Questions:
- A ship has a steel hull. Steel is much denser than water, yet the ship is able to
float. Why?
- How could you make an object that is less dense than water sink? How could you
make an object that is denser than water float?
- Why would life jacket designers use materials with very low density?
5. Understand the concept of pressure.
Sample Questions:
- A fluid exerts pressure on the walls of its container in… a) only one direction or
b) equally in every direction.
- Why does a fluid exert pressure? (Think of what the molecules are doing.)
- A balloon is filled with air and then placed in the freezer. Will the balloon likely
shrink, expand, or stay the same size?
- Why might your bicycle’s tyres seem flatter on a cold day?
- Why do aerosol (spray) cans say “contents under pressure – do not heat?” What
would likely happen if you did heat the can?
- Why do your ears hurt when you dive too deeply under water? What can you do
to stop your ears hurting?
- In water, the pressure doubles every 30 feet you go down. If the pressure at the
surface of the water was 101.3 kPa, what would it be 30 feet down? 60 feet
down?
- Why does the pressure increase the deeper you go in a fluid?
- What would the pressure be at the very edge of the earth’s atmosphere?
- If you fill a syringe with water and plug the end, will you be able to force the
plunger down? What if he syringe is filled with air?
6. Know the difference between hydraulic and pneumatic machines and be able to
identify examples of each.
Sample Questions:
- An air bag inflates with air if a car crashes, protecting the driver or passenger
from hitting their head on the steering wheel or dashboard. Is this an example of
a hydraulic or a pneumatic machine?
- Which is noisier, a hydraulic machine or a pneumatic machine?
- Which fluid is normally used in hydraulic machines? What about pneumatic
machines?
- A car jack lifts a car when the operator slowly forces oil from a larger container
into a smaller one, causing a piston to push the car up. Is this an example of a
hydraulic or a pneumatic machine?
- *This question will be on the test: Choose one of the hydraulic or pneumatic
machines mentioned in the YouTube video that we watched. Draw a labeled
diagram and use it to explain how the machine works.
Note: YouTube video addresses: http://www.youtube.com/watch?v=YlmRa-9zDF8
and http://www.youtube.com/watch?NR=1&feature=endscreen&v=UuK3ESGgbqk
7. Practical: You will be given two substances, a liquid and a solid, plus a scale and
volumetric cylinders. You will need to find the density of each of those substances.