Energy and Machines Notes
Topic one
What is a machine? A machine is any device, simple or complicated, that uses
energy to perform a useful task or function.
A screw driver is an example of a machine.
Energy is defined as the capacity to do work, or transfer heat.
Work is defined as the result of a force being exerted on an object and the object
moving in the general direction of the force. Two condition required for work to be
done are (1) a force is exerted on the object, and (2) the object moves for a
distance in the general direction of the force.
Force is measured in Newtons. Therefore work is measured in Newtons (N).
Imagine the situations described. One group of people have lifted a rock from the
ground to the bed of the truck, while another group struggles to move a car stuck
in the mud (they do not move the car). Which of these groups is actually
accomplishing work?
The group that actually lifts the rock into the flat bed of the truck has performed
work. If you look at the conditions required in the previous question is states that
there must be movement in the general direction of the force. There is no
movement with the people pushing on the car that is stuck, therefore there is no
work accomplished.
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SYSTEMS AND SUBSYSTEMS
Are all machines complicated? No. All machines are made up of the SIX most
basic machines, which are...
1. Ramp
2. Lever
3. Pulley
4. wheel-and-axle
5. Wedge
6. Screw
A complicated machine can be thought of as a system. Its working parts make up
the subsystems of the machine.
Another name for the simple machine called the inclined plane is Ramp
Another description for the simple machine called the pulley is the Rotating wheel
with a groove
When you pull on a wagon or push on a car that is stuck in the mud you are
exerting a force on that object. This force that you exert is called the effort force .
A fact that holds true at all times is that the earth's gravity will always exert 10
newtons of force on every 1 Kg of mass. A force exerted by gravity on a block of
wood that is .38 Kg or 380 grams (REMEMBER THAT 1 Kg= 10 N) is equal to
3.8 newtons.
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There is a strong advantage to combining the two different types of simple
machines. The overall effort needed to complete a task is significantly reduced.
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TOPIC TWO - EASING THE TASK WITH LEVERS
Archimedes is "quoted" as saying, "Give me a lever long enough and a placeto
stand and I will move the earth." So what is a lever system? The Greek scientist
Archimedes once claimed that if he had a point of support, he'd be able to move
the world. He was referring to the lever's amazing ability to make heavy lifting
easier
A ramp or a pulley can reduce the force you need to exert (Effort force).
a Lever is another effort-reducing device.
What types of jobs can a lever help you complete?
1. Hitting a baseball.
2. Opening a bottle of pop.
A lever is an effort-reducing simple machine.
Below are three different tools that incorporate the idea of a lever into their
design.
1. A pair of pliers.
2. A golf club.
3. A pair of scissors.
A fulcrum is the point that supports the lever and upon which it turns, or pivots.
There are three classes of lever. They are determined by the position of
the fulcrum, effort force, and load.
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1. Class 1 Lever - When a lever’s fulcrum is between the load and the effort
force. This lever can also be called the Children's lever. Think about a fun park
toy that kids play on.
Ex. - A TEETER-TOTTER
In a first class lever the fulcrum is between the effort and resistance, where the
lever exerts a force.
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2. Class 2 Lever - When a lever’s fulcrum is at one end, the load in the middle
and the effort force at the opposite end from the fulcrum. You could also call this
the gardener’s lever.
Ex. - A wheelbarrow
In a second-class lever the resistance is between the fulcrum and effort. For such
levers, if the effort arm is longer than the resistance arm, less effort over a certain
distance exerts a greater force over a shorter distance.
3. Class 3 Lever - When a lever’s effort force is between the fulcrum and the
load. This could also be called the sportsman's lever. Racquet sports such as
tennis, badminton, and fishing require the use of a rod shaped tool. The fulcrum
is at the wrist and the effort force is throughout the length of the rod and the load
is on the very end.
Ex. - An arm lifting a book. Kicking a soccer ball.
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In a third-class lever the effort is between the fulcrum and the resistance. More
effort is required to move less weight, but the speed and distance moved are
increased
SO WHAT THREE IMPORTANT FACTS HAVE YOU'VE LEARNED ABOUT
LEVERS?
1. There are three types of levers
2. They are formed by varying the arrangement of three things: the load, the
fulcrum. and the effort force.
3. The arrangement of these three things depends on the lever’s function.
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TOPIC THREE - THE WHEEL AND AXLE
Imagine trying to open a door without a doorknob! Another simple machine at
work here and it is called a wheel and axle. This simple machine is used to
overcome a large force by applying a smaller effort force, this is called a FORCE
ADVANTAGE. But, there are instances where a wheel and axle is used to
increase speed, which is called SPEED ADVANTAGE. One example of speed
advantage is found on a 21 speed mountain bike.
TOPIC FOUR - COMPLETING YOUR SURVEY OF SIMPLE MACHINES
What four types of simple machines have we just looked at?
1. The ramp
2. The pulley
3. The lever
4. the wheel-and-axle
What is the differences between a wedge and an inclined plane?
A wedge is similar to an inclined plane, except that a wedge normally moves into
an object (for example, an axe head cuts into a block of wood), while an inclined
plane stays still and objects move along it.
What is the sixth type of simple machine?
The screw.
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TOPIC FIVE - EXAMINING MECHANICAL DEVICES
Mechanical devices are usually made up of large numbers of such simple
machines .
Do systems always need to have a constant energy supply? NO. Some systems
have their energy supplied by outside sources, and only require energy when the
device is in use.
What is the main subsystem of a stapler? The main subsystem of a stapler uses
a lever.
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TOPIC SIX - USING GEARS
What is a GEAR WHEEL?
A gear wheel is a wheel with precisely manufactured, identical teeth around its
edge.
What does a gear wheel do? A gear wheel is used to transfer rotary motion and
force from one part of a machine to another part.
What does the term mesh mean in simpler terms? Mesh means to interlock
neatly.
A smaller gear is called a pinion. The gear that supplies the energy is called the
driving gear.
The gear to which the force is directed is called the driven gear.
MULTIPLYING GEARS AND REDUCING GEARS
A large gear driving a smaller gear decreases torque and increases speed in the
driven gear
A small gear driving a larger gear increases torque and reduces speed in the
driven gear
What is a reducing gear? When the driving gear has fewer teeth than the driven
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gear, the driven gear then rotates more slowly than the driving gear. Such gears
are called reducing gears, because they reduce turning speed. A car or bicycle in
low gear uses reducing gears.
When the driving and the driven gears are the same size these gears are known
as parallel gears .
Do parallel gears both move in the same direction when moving? (HINT: Do both
move in a clockwise direction when moved?) Explain.
NO. When the driving wheel spins in a clockwise direction it moves the driven
gear in a counter-clockwise direction.
GEARS IN A BICYCLE
Machines use gears to change forces. The
bicycle is the most efficient machine ever invented for converting human muscle
power into motion. Bicycles use gears and levers to connect the muscle power
from your legs to turning the rear wheel. The connection is made with a chain so
that the gear ratio between the crank and the freewheel can be changed while
the bicycle is moving. Modern bicycles have between one and 24 different
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speeds. Each speed corresponds to a different gear ratio.
Why are some gears easier to pedal than others? Why do some gears allow you
to go faster than others?
What are sprockets? The gears that are actually toothed discs.
Where is the front sprocket located? The front sprocket is attacked to the pedal
crank (where your foot is located)
Where is the rear sprocket located? The back sprocket is attached to the hub
(axis) of the rear crank - the middle of the back wheel.
When would you use first gear? When you're trying to go up a very steep hill.
You turn the pedal like crazy and you do not move very fast or far for your effort,
but you do not exert a great deal of effort throughout the climb either.
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TOPIC SEVEN - SOURCES OF ENERGY TO RUN MACHINES
What is one form of energy used in machines, besides the power of our human
bodies? Chemical energy. Mostly all energy originates as Solar energy, from out
Sun. Some energy is geothermal, which supplies tube worms and other
subterranean and oceanic life.
SOME FORMS OF ENERGY
What is thermal energy? The total energy of all the particles in a material or
object.
What is potential energy? Potential energy is actually stored energy.
“AVAILABLE ENERGY.”
What is kinetic energy? Energy of motion is Kinetic Energy.
What is elastic potential energy? Elastic Potential energy is the energy stored in
a wound up spring.
What is mechanical energy? Mechanical energy is a type of energy we associate
with mechanical devices. It can be kinetic (when the parts of the device are
moving) or potential (when a grandfather clocks pendulum is at the top of its
swing, its energy is potential energy).
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What does an energy converter do? It converts energy from one form to another.
For example, solar powered energy can be converted to electrical energy.
THE LAW OF CONSERVATION OF ENERGY
What is the law of conservation of energy? Although energy may change its form,
it is never “created” and never “destroyed.” Scientists say that energy in a system
is “conserved.” this means that energy is neither created nor destroyed, but
transformed (changed from one form to another).
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TOPIC EIGHT - ENERGY USE AND EFFICIENCY
How many devices will you use today that will do work for you, provide you with
heat or light, or entertain you? Most of these devices use electrical energy to
produce some other form of energy. Some devices use the chemical energy of
fuels such as natural gas, wood, or gasoline.
If you were given a gasoline engine in a car that produced only 15 Kj of useful
mechanical output energy for every 60 Kj of chemical input, its efficiency would
be......?
What percentage does this number represent?
15 Kj/60Kj = 0.25 this means that the efficiency of the engine is 25%.
The energy that is not put to useful work is wasted.
Are incandescent light bulbs efficient? NO. The majority of the energy is lost as
heat.
MEASURING EFFICIENCY
Efficiency is equal to (energy produced by the device) divided by (energy used to
operate the device) and this number is then multiplied by 100%.
Ex. The above engine is only 25% efficient.
How can you figure out the efficiency of many household devices?
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You look for the special label on them with an “energy use” rating called the
Energuide number. This number tells you how much electrical energy the device
will use, on average, in a month.
The efficiencies of Some Heat Engines
Heat Engine Efficiency
Airplane engine 10 %
Steam locomotive 10 %
Automobile engine 22 %
Steam turbine 30 %
Diesel engine 35 %
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