Unit 4
Mechanical Systems
Section 1.0 Machines are tools that help humans do work.
Define:
machine-
1.1 Simple Machines- Meeting Human Needs
Water Systems
Then:
The earliest devices were
_____________ devices. Each machine was
designed to meet ______________ needs.
They all had one thing in common, they all
depended on _______________ or
____________________ for their source
of _______________.
Parts of a Roman Aqueduct:
1.
Now:
Main Components:
1.
2.
How is gravity used to maintain pressure?
2.
3.
Two methods used to raise water levels:
1.
2.
Two examples of the Archimedes screw in
use today:
1.
2.
Define:
simple machine-
Complete the following table of the six simple machines:
(The advantage and disadvantage columns will be filled in together as a class when we are going
over the worksheet)
Simple Machine and
Description
Advantages
Disadvantages
Example
**General Rule:
If you have an effort force advantage, you have a ____________________ disadvantage.
If you have a speed and distance advantage, you have an _______________ disadvantage.
Name the three different classes of levers, describe how each looks using the terms:
fulcrum, load force, and effort force, draw a diagram to illustrate each and give two
examples of each.
i) ______________________-
Examples:
ii) ______________________-
Examples:
iii) ________________________-
Examples:
Look at the diagram at the top of page 262. If A is 10 times the distance of B from
the fulcrum, the person will use ____________________ of the force needed to move the
object without a lever.
Effects obtained by
simple machines
Do Check and Reflect- p. 268- #1, 2, 4
1.2 The Complex Machine- A Mechanical Team
Complex
machine -
System -
Subsystems -
Use the bicycle to explain the terms complex machine, system and subsystems.
Read Give It a Try- p. 271 and answer the three questions about the pencil
sharpener.
Name and Describe two subsystems that transfer forces:
Read “reSearch” – p. 273. Ask your parents, or a friend to help you answer the
questions about automatic and manual transmissions.
Define
GEAR WHEEL:
Define
GEAR:
Gears can be used to:
1.
2.
3.
4.
Gears are important in mechanical systems because they control the
__________________ of __________________ in the system.
6.
7.
8.
9.
The gear that applies
Define GEAR TRAIN:
10.
the force is:
11. Gears are important in mechanical systems because they control the ___________
of_____________ in the system.
12. a)
Define:
gear train-
The gear that moves
as a result of the
force is:
Complete the statements:
a) If the _____________ gear is larger than the ____________ gear, the turning
speed of the system increases, and are called ___________________ gears.
b) If the _____________ gear is smaller than the ______________ gear, the turning
speed of the system decreases, and are called ___________________ gears.
In a ten-speed bicycle:
a) the driving gears are found at the _______________ and the driven gears are
found at the _________________.
b) when you are in first gear, the __________ gear is large and the __________ gear is
small.
c) when you are in tenth gear, the driving gear is _______________ and the driven gear
is _________________.
d) first gear can be described as a (multiplying reducing) gear system.
e) tenth gear can be described as a (multiplying, reducing) gear system.
Which gear would you use to:
i)
ii)
pedal up a very steep hill? _________________________
pedal down a stretch of very flat highway? ____________________
Do Check and Reflect- p. 276- #2, 3-a,b
Do Assess Your Learning- p. 277- #1, 2, 4, 5-a,b
Section 2.0- An understanding of mechanical advantage and work helps in determining the efficiency
of machines.
2.1 Machines Make Work Easier
Read Infobit, p. 279.
a) What simple machine is being incorporated into the construction of the road up the mountain?
b) Talk to your parents, friends of the family or research for yourself. Can you find any other places that
show this simple machine being used within the construction of a highway/roadway?
Force
Definition:
Unit:
Symbol:
Named after:
One newton is equal to the amount of force exerted by earth’s gravity on _____ g or ______ kg.
Mechanical Advantage
Speed / Speed Ratio
Definitions
mechanical advantage-
speed-
input forcespeed ratiooutput force-
In the car, on p. 279, the __________________
force is the force applied by the person and the
______________ force is the force applied to the car.
The__________________ force is larger than the
_________________ force.
Define:
input distance-
output distance-
Mechanical Advantage
Speed / Speed Ratio
Calculations:
In order to calculate mechanical advantage, you
To be able to calculate the speed ratio, you
need to know the _____________________ and
must know the _____________ distance and the
___________________, both of which are in newtons.
_______________ distance.
Formula:
Formula:
Mechanical advantage = _______________________ Speed ratio = _______________________
OR
OR
M.A. = _______________________
S.R. = _______________________
Calculate the mechanical advantage when it
takes 30 N of force to lift a 300 N object.
When the mechanical advantage is greater than
1, the input force is (more, less) than the output force.
When the mechanical advantage is less than 1,
the input force is (more, less) than the output force.
When the mechanical advantage is less than 1,
the machine is useful for tasks that don’t require a
_____________ _____________ _______________.
Calculate the speed ratio when an object is
lifted 2 m by a pulley system and the rope was pulled
10 m.
A speed ratio of 4 means that the
___________ force moves ______ times faster than
the ____________ force.
Read “Less force but greater distance”, and
then calculate the speed ratio for each ramp.
Read the fourth paragraph from the top, on
Ramp 1 –
page 282, about the mechanical advantage of a
bicycle. Is the bicycle a useful machine? Explain why.
Ramp 2 –
Mechanical Advantage
Speed / Speed Ratio
Friction:
Define –
When moving an object with a simple machine,
the (input, output) force includes the force necessary
to move the object and the force needed to overcome
____________________.
The speed ratio represents the
______________ mechanical advantage, because
________________ does not affect its calculation.
This means that the theoretical mechanical
advantage will be (less, more) than the real or actual
mechanical advantage.
Affected by friction?
Yes
Why or why not?
No
Yes
Why or why not?
Friction in a mechanical system results in a need for (more,
less) input force, and also creates__________________. The heat
comes from the two surfaces __________________ against each
other and can be reduced by using __________________.
No
Mechanical Advantage
Speed / Speed Ratio
Efficiency
Define:
In any machine some of the energy is “lost” to ___________, therefore it is not directly used for the task.
The more energy that is lost, the less ________________ a machine is. Efficiency is calculated as a
_____________________.
Calculations:
Formula:
Efficiency = _______________________
OR
Efficiency = ___________
Calculate the efficiency of a pulley that has a mechanical advantage of 4 and a speed ratio of 5.
Because of ______________ in the _____________________
of complex machines, they are often very inefficient.
Explain why the efficiency of a typical automobile engine is so low.
Do Check and Reflect - p. 286- #1, 2, 3, 4, 5
2.2 The Science of Work
Work
Work Input / Output
Define:
work-
Define:
work input-
Is work being done in each of these situations?
Explain why or why not.
i)
work output-
Figure 2-10, p. 288 -
Read Figure 2.12. In the car, energy from
________________ provides a force that makes the
ii) Figure 2-9a, p. 287 -
different parts of the car to move together causing the
car’s ____________ to move.
Calculations:
Formula:
Formulas:
Work = _______________________
Work input = _______________________
OR
Work output = _______________________
Work = ______________
In the above formula, the force is in units called
________________ and the distance is in units called
________________.
200 N
90 N
3m
12 m
The unit of work is the ____________________,
which is called a _______________.
The amount of work done depends on two
factors. They are:
i)
ii)
Using the diagram above as a reference:
Calculate the work input when 90 N of force moves
an object 12 m.
Calculate the amount of work that is done when
a force of 80 N is used to lift an object 3 m.
200 N
90 N
For a bicycle, _____________ is being done
12 m
Using the same diagram above as a reference:
Calculate the work output when a 200 N object is
lifted 3 m.
because your ____________ provides a force which is
applied to the pedals causing the bicycle to
______________ over a distance.
Do you think the work input and the work output will be equal
most of the time? Read P. 292.
Efficiency
Efficiency can be calculated another way, using work input and output:
Efficiency:
3m
_____________________
Calculate the efficiency for the ramp/inclined shown above.
Do Check and Reflect - page 292- #2, 6, 7, 8 & 9
2.3 The Big Movers- Hydraulics
Before hydraulics
were invented, how were
construction projects done?
Give two examples to illustrate this.
Hydraulic SystemDefine:
Give four examples of where
hydraulics are used today.
1.
2.
3.
4.
Pressure
Definition:
Formula:
Pressure = _________________
Unit:
Symbol:
Larger Unit:
or
P = _____
Symbol:
Pascal’s Law states that ______________________________________________________________
_______________________________________________________________________________________.
Pascal’s Law explains why these two
types of systems work.
Hydraulic systems use ________________ and pneumatic systems use _____________.
A common application of Pascal’s
Law is the _______________
____________, which is used to
____________________________
In hydraulic systems, the pressure is
created by using a ________________,
Hydraulic devices use a combination of
Hydraulics
which moves inside of a
________________, and it either
______________ fluid out of the
_______ pistons attached to either end
of a __________________ or flexible
and
Pascal’s Law
pipe. The piston that the force is applied
to is the __________________ piston
and the pressure is transferred to the
cylinder or it _________ fluid into it.
other piston- the _____________ piston.
The pressure on the
_____________________ piston is
equal to the pressure created by the
_________________ piston.
Calculate the mechanical advantage of a hydraulic system which looks like the one on p. 298. The force
on the input piston is 30 N and the force of the outward piston is 600 N.
The reason for the large mechanical advantage in a hydraulic system is
The force and area at each piston, as ratios, have to be _____________.
Pascal’s Law→ Pressure large = Pressure small which is the same as Force large = Force small
Area large
Area small
Using the formula above, calculate what the force on the large piston would be if the large piston has an
area of 50 cm2 and the small piston has a 40 N force applied to an area of 10 cm2.
In simple machines, the mechanical advantage comes at a cost. That cost is:
Do Check and Reflect- p. 300- # 2, 4
Do Assess Your Learning- p. 303- # 2, 3, 4, 5, 6
Section 3.0 Science, society, and the environment are all important in the development of mechanical
devices and other technology.
3.1
Evaluating Mechanical Devices
When manufacturers evaluate a device they make, what types of criteria might they use in this evaluation?
Name five.
i)
iv)
ii)
v)
iii)
Read “Using Criteria to Evaluate a Device.” List the criteria that might be important to someone wanting to
buy a bicycle.
Efficiency:
What’s the
difference
between

Define:
FunctionDesign-
Effectiveness:
Explain what this means. “An important aspect of evaluating mechanical devices is ensuring that the
design suits the function.”
Using the bicycles in Figure 3.3, answer the following:
a) The primary or main use of the bicycle on the left is ____________________________________________
b) The primary or main use of the bicycle on the right is ___________________________________________
Complete the table of design features for bicycles, by stating how each is different and the reason for the
change for each type of bicycle.
Design Feature
Cross-Country Bicycle
Road Racing Bicycle
Tires
Frame
Handle bars
Three reasons for doing a thorough evaluation of a mechanical device are:
a)
b)
c)
Reason
The effect of a device on the environment should also be considered in evaluating a device. Give two
examples of this being done from p. 308.
As you read through the sections on pop can openers (P. 310- 311), complete the table below.
Opener Design
Advantages
Disadvantages
Church Key
Removable Tab Top
Buttons
Non-removable Tab Top
Read “reSearch”- p. 312.
a) What do the letters CSA stand for?
b) What is the CSA?
c) Are there any other organizations that test devices for safety and value? If there are, name some of them.
Do Check and Reflect - p. 314- #2, 3, & 4.
3.2
Technology Develops Through Change
The changes in the pop can opener resulted from both ___________________ and
_____________________ needs. Also new ________________ and _____________________ contributed to
its development as well as new ___________________ of making the cans.
Look at the sewing machines on page 315.
Compare the original and the second
machine…
Compare the second and the third machine…
What changes
were made?
Why?
Read Infobit- p. 315.
a) What device was developed that is still in use in vehicles today?
b) What was the purpose of this invention and how has it been changed today?
Explain how each of these resulted in a new technology.
Advances in science, specifically advances
in electrical knowledge. (p. 316)
Research in particle physics and the use of
particle accelerators. (p. 316- 317)
New technology that results from changes
to human society. (p. 317)
Changes in the environment result in new
technology. (p. 319)
The purpose for creating robots was to
A very simple robot contains some, or all of these basic parts. Name them.
i)
ii)
iii)
iv)
v)
vi)
Read “Careers and Profits”, p. 320. What did Peter Robertson invent and why was it an important
invention?
Name and draw the head of the three most common screws used today.
Do Check and Reflect - p. 320- #1, 2, 3
Do Assess Your Learning - p. 321- # 2, 3, 4
Do Focus on Science And Technology- # 2, 3
Do Unit Review- p. 325- # 4, 5, 6, 7, 9, 10, 11, 12, 13, 14, 18, 19, 21, 23, 24, 25