PSAA Curriculum
Unit
Physical Science Systems
Problem Area
Energy and Power Systems
Mechanical Power
Transmission
Lesson
What are some various agricultural
applications that utilize mechanical
power?
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What is the location of the power source
and is the power applied at the rear axle?
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Is the speed and direction of the applied
power the same as that of the source?
Learning Objectives
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Define force, torque, work, power, and
energy and explain their relationship to
each other and mechanical power
transmission.
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Determine the relationship between
diameter and number of teeth on a gear or
sprocket and the speed and torque of the
gear or sprocket.
Learning Objectives (cont.)

Apply the Law of Conservation of Energy
to power, torque, and speed relationships
for mechanical power transmission.
Terms
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Acceleration
Energy
Force
Gear
Gear ratio
Horsepower
Kinetic energy
Mass
Newton
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Newton’s second law
Potential energy
Power
RPM
Torque
Torque wrench
Watt
Work
What is the definition of force,
torque, work, power, and energy and
how do they relate to each other?
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Force can be defined as a push or pull that
tends to start, stop, or change the direction of
motion of an object.
Force will vary depending upon gravitational
forces.
That is the reason our weight can vary from the
earth to the moon due to the lower amount of
gravitational pull on the moon thus making us
weigh less on the moon versus the earth.
Mass
However, mass (the amount of matter in
an object) is the same no matter what
location we are at on this planet or any
planet.
 Gravity is a force that acts upon an object.
 The more mass an object has, the greater
the force of gravity that acts upon the
object.
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Acceleration
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Force causes acceleration.
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The more force you apply to an object, the
greater the rate of acceleration.
Newton’s Second Law
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Newton’s Second Law summarizes that
the acceleration of an object is directly
proportional to the force applied to the
object and inversely proportional to the
object’s mass.
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The more mass and object contained, the
lower the rate of acceleration.
Newton
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To honor Sir Isaac Newton, the newton
was adopted as the SI unit of force.
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One newton of force can accelerate one
kilogram of mass at a rate of one meter
per second per second.
Torque
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The force that tends to cause objects to
rotate or turn is torque.
When we use a wrench, we apply force to
the handle.
 This force creates rotary motion or torque
on the nut, which turns the nut to tighten or
loosen.
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Torque
When calculating torque, the force applied
is multiplied by the distance from the
center (radius).
 English units of torque are inch-pounds or
foot-pounds.
 The SI units are expressed as newtonmeters, in honor of Isaac Newton.
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Torque
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A torque wrench is used by a
mechanic to tighten nuts and bolts
to prevent them from loosening
during engine vibration.
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The torque wrench can be
adjusted to deliver the
recommended amount of force to
cylinder head bolts on a
lawnmower engine without over
tightening.
Torque
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If the wrench is one foot long and we apply
100 pounds of force on it when tightening,
we are generating 100 foot-pounds of
torque.
Work
Work is the application of force to an
object that causes the object to move in
the direction of the force being applied.
 Lifting an object from the ground and
placing it on a shelf is an example of work.
 The force being applied equals the weight
of the object being lifted and the distance
equals the height from the ground to the
shelf.
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Work
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Work equals force multiplied by distance.
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The units most often used to express work
are foot-pounds or newton-meters.
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Work is energy that has been used.
Work
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Power is a measure of how quickly work
can be done.
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Power equals work divided by the time.
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The SI (International System) unit for
power is the watt.
Work
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One watt is equal to one newton-meter of
work completed per second (N×m/s).
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If we pushed on an object with one newton
of force, and moved it at a speed of one
meter per second, our power output would
be one watt (1 N × m/s).
Work
A horsepower is equal to 746 watts.
 One horsepower is equivalent to 550
footpounds or work performed in one
second or 33,000 foot-pounds of work
done in one minute.
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Energy
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Energy is the capacity to do work.
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Energy is a measure of how long you can
sustain your power output.
Energy
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Potential energy is waiting to be
converted to power.
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Compressed springs, gasoline, food in
your stomach, a skier at the top of the
slope, are all examples of potential energy.
Energy
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Kinetic energy is energy of motion. Any
object that is in motion has kinetic energy.
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The more an object weighs, and the faster
the object is moving, the greater the
kinetic energy the object possesses.
Belt Velocity and Belt Force
What is the relationship that exists
between the diameter and number
of teeth of a gear and the speed
and torque of the gear?
A gear is a toothed wheel used to transmit
power.
 Gears are used for four main reasons: 1)
reverse the direction of rotation, 2) increase or
decrease the speed of rotation, 3) move
rotational motion to a different axis, and 4)
keep the rotation of two axes synchronized.
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Gears
The gear ratio is determined by the
distances from the center of the gear to
the point of contact.
 If one gear is three times the diameter of
the other, the ratio would be 3:1.
 This means that for every one revolution of
the larger gear, the smaller gear will rotate
three times in order to cover the same
distance as the larger gear.
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Gears (cont.)
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The majority of gears contain teeth.
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The teeth have three advantages on
gears: 1) maintain synchronization and
prevent slippage, 2) eliminate the concern
about slight imperfections in diameter and
circumference, and 3) make it possible to
calculate exact gear ratios by counting the
number of teeth and divide.
Gears (cont.)
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For example, if one gear has 50 teeth and
the other gear has 25 teeth, the gear ratio
between the two gears is 2:1.
Gears (cont.)
Gears have many uses in mechanized
devices.
 One of their most important uses is to
provide gear reduction to help with power
and torque requirements.
 A small motor is usually spinning fast
enough to provide speed and power but
not enough torque.
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Gears (cont.)
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Gear reduction can be implemented in a
device to reduce the output speed and
subsequently increase the torque of the
machine.
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If the power is constant in a machine,
torque and speed are inversely related,
meaning that a reduction in one will result
in an increase in the other.
Gears (cont.)
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The diameter and number of teeth on a gear or
sprocket is also inversely related to speed,
meaning the larger gear with more teeth will spin
at a slower speed.
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Speed of gears is measured in
revolutions per minute (RPM).
What is the Law of Conservation of
Energy and how does it affect
power, torque, and speed
relationships?
Energy cannot be created or destroyed.
 Whenever work is done, the work appears
as potential energy, kinetic energy, and
horsepower, or the combination of all
three.
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Law of Conservation of Energy
The energy input to a system must equal
the energy output.
 The horsepower of most power sources
used for agricultural applications is finite.
 Trade-offs must be made between torque
and speed (RPM) when the power is
transmitted.
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Review/Summary
What is the definition of force, torque, work,
power, and energy and how do they relate to
each other?
 What is the relationship that exists between
the diameter and number of teeth of a gear
and the speed and torque of the gear?
 What is the Law of Conservation of Energy
and how does it affect power, torque, and
speed relationships?
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