Unit 4 Mechanical Systems

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Unit 4 Mechanical Systems

• Topic 1
• Levers and Inclined Planes

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• A lever is a simple machine.

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• A lever has 3 components
• Fulcrum fixed point on which the lever pivots
• Effort Force the force that you exert on a
  lever
• Load the mass of an object moved or lifted

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• Effort Arm distance between the fulcrum and the
  effort force
• Load Arm distance between the fulcrum and the
  load.

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• Levers are sorted into 3 different classes
  depending on the positioning of the fulcrum,
  effort force, and load.

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• Class 1 Lever Fulcrum is between the effort and
  the load. Gives you a power advantage.
• (Makes lifting/
• Moving things
• Easier)

Effort Force
Fulcrum
Load
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• Class 2 Lever Load is between the effort and
  the fulcrum. Gives you a power advantage.
• (Makes lifting/
• Moving things
• Easier)

Effort Force
Load
Fulcrum
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Fulcrum

• Class 3 Lever Effort is exerted between the
  fulcrum and load. You must exert a greater force
  on the load, but the load can
• be moved very
• quickly.

Load
Effort Force
Load
Effort Force
Fulcrum
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Identify the class of lever used in each of the
following machines

• Scissors
• See-saw
• Hockey Stick
• Nut cracker
• Pliers
• Broom
• Wheel barrow

Class 1
Class 1
Class 3
Class 2
Class 1
Class 3
Class 2
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HOW CAN WE REMEMBER EACH CLASS OF LEVER?

• CLASS 1 E-F-L EFL
• the
• CLASS 2 F-L-E FLE
• CLASS 3 F-E-L FEL
• EFL the FLE FEL

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• WORK!?
• In SCIENCE when you exert a force on an object
  AND move it in the direction of the force, you
  are doing work.
• Work Force x Distance

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• Like energy, work is measured in joules (J).
• 1J moving 1N a distance of 1 meter.
• 1N 100 grams.

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• Calculate the work
• You pull your hockey bag from your car to the
  dressing room. Your bag weighs 125 N. You have
  to walk 45 metres. How much work have you done?

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• Work Force x distance
• Work 125 N x 45 m
• Work 5625 J

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• NOW, say you carry hockey bag from your car to
  the dressing room. Your bag weighs 125 N.
• You have to
• walk 45 metres.
• How much work
• have you done?

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• NONE! ZIP! NIL! ZILCH!
• You were exerting a force upward on the backpack
  so it would not fall on the floor. However, you
  did not move upward. You moved in a horizontal
  direction.

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• The Inclined Plane (Ramp)
• - a ramp or slope that reduced the effort you
  need to exert to lift something, just as you saw
  in the previous two illustrations.
  Unfortunately, you usually increase the distance
  when you decrease the effort to move a load.

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• INPUT WORK the work you do on a machine.
• OUTPUT WORK the work machine does on a load.

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• MECHANICAL ADVANTAGE
• Mechanical advantage is simply how many times
  easier a machine makes it to move something.

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MA Formula

• MA Load force
• Effort force
• So, if you use a lever to lift a 5000N object,
  and you must exert 500 N of energy, the MA
  achieved is 10.

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?
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Unit 4 Mechanical Systems

• Topic 2
• Wheel and Axle, Gears, and Pulleys

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• Wheel and Axle
• The wheel and axle is a large wheel and a smaller
  wheel mounted on a common axis so that the wheels
  rotate together.
• Wheel larger
• Axle - smaller

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• A wheel and axle can provide a mechanical
  advantage remember that this means that you
  will receive more effort from the machine than
  the amount of effort you put into it.
• Eg. Door knob, steering wheel

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• In order to get this mechanical advantage, your
  effort must be applied to the wheel. (remember,
  this is the bigger one)

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• A wheel and axle can also provide a speed
  advantage.
• Riding a tricycle would be a good example. You
  apply your effort to the axle (pedals), which is
  connected to the wheel, and you gain speed. You
  must put out a large effort force.

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• Gear
• A gear wheel is a wheel with identical teeth
  arranged around its edge. It is used to transfer
  force to another gear wheel.
• A gear train consists of two or more gear wheels
  that mesh so that rotary motion and force can be
  transferred to another gear.

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• The larger gear in a gear train is called the
  gear wheel.
• The smaller gear in a gear train is called the
  gear pinion.

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• Driving gear (driver) turns due to motor,
  human, etc.
• Driven gear (follower) turns because it is
  attached to the driving gear.

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• Multiplying gears consist of a large driving gear
  with a small driven gear that combine to provide
  an increase in rotational speed.
• Reducing gears consist of a small driving gear
  with a large driven gear to provide a decrease in
  rotational speed.

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• Can gears turn without touching each other?
• Think about a bike. The two (or more) gears are
  attached by a chain. These gears are called
  sprockets.

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• The effort force is on the front sprocket.
• The rear sprocket is the driven gear.

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• DONT WRITE
• If the front sprocket on a bike has 45 teeth, and
  the back sprocket has 15 teeth, how many times
  will the back sprocket turn with one turn of the
  front sprocket?
• ANSWER ?

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• 3
• You just solved what is called a speed ratio.
  This is the relationship between the speed of
  rotations of a smaller gear and a larger gear.

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• Speed ratio of driver gear teeth
• of driven gear teeth

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• PULLEY
• A grooved wheel with a rope or chain running
  along the groove.

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• Fixed pulley does not move and is attached to
  something like a ceiling. It simply changes
  direction of the effort force.
• Moveable pulley often attached to a ropethe
  rope is then fixed to the ceiling.

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• The more pulleys you use, the greater the
  mechanical advantage will be that you will gain.

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• To calculate the MA of a pulley system, count the
  number of rope segments, but do not count the
  rope being pulled down.

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Dont count
1
3
4
2
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• Pulleys are used to
• reduce the effort force needed to lift a load or
• to allow the lifting of a load by pulling down
  rather than lifting up.

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Unit 4 Mechanical Systems

• Topic 3
• Energy, Friction, Efficiency

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• Kinetic energy energy present in moving
  objects.
• Potential energy stored energy
• Potential Energy is energy that is stored in
  something and is potentially available.
• There are many forms of potential energy.

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• Some forms of energy
• Thermal energy (heat) is the total energy of all
  the moving particles in a material or object.
• Chemical energy is the energy stored in foods and
  fuels.
• Mechanical energy is the energy associated with
  machines

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Some Other Forms of Energy

• Solar Energy
• Sound Energy
• Tidal Energy
• Gravitational Energy
• Light Energy
• Wind Energy

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• An energy converter is any device that can
  convert energy from one form to another.
• An energy transmitter, energy is transmitted from
  one place to another, but no energy is converted.

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• The school bell converts chemical energy to
  mechanical energy to sound energy.

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• The mechanical mouse converts chemical energy
  (from our bodies) to mechanical energy.

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• What conversion happens in a solar heater?
• A solar heater converts light energy into heat
  energy.
• (Or light into electrical)

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• What energy conversion takes place in a toy
  rocket?
• The rocket changes chemical energy to mechanical
  energy, heat energy, light energy and sound
  energy.

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• The efficiency of a machine tells you how much of
  the energy you gave to the machine was
  transferred to the load by the machine.
• Efficiency output energy
• input energy

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• Every time a machine does work, some energy is
  lost due to friction. (Ie. Blades on scissors
  rubbing together.)
• Make machines more efficient by reducing friction
  adding lubricant such as oil or grease.

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Unit 4 Mechanical Systems

• Topic 4
• Force, Pressure, Area

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• Pressure the force acting over a certain area.
• SNOWSHOES without them you break through snow.
  With them, your weight is spread over a larger
  area, which reduces pressure.
• Think of a boat on water, hockey equipment, bed
  of nails.

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• PRESSURE Force
• Area
• Measured in N/m2
• Newtons / metre squared

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• Pascals Law
• Think of what happens when you squeeze a
  water-filled balloon.
• Pascals Law states that pressure exerted on a
  contained fluid is transmitted undiminished in
  all directions throughout the fluid.

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• Hydraulic lift raises heavy objects, such as a
  vehicle at a garage. Uses Pascals Law.
• Hydraulic lift uses fluid under pressure in a
  closed system

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9 times larger so transmits 900N/cm2 (PA) of
force!
Transmits 100N/cm2 (PA) of force
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• Mechanical Advantage of Hydraulic Lift
• If you exert 10N of force on the lift, and it
  lifts 120N of force on a load, then the MA is 12.
  
• Load Force 120
• Effort Force 10 12

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Unit 4 Mechanical Systems

• Topic 5
• Hydraulics and Pneumatics

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• Hydraulic Systems use the force of liquid in a
  confined space.
• This works because of a liquids
  incompressibility and its ability to transmit
  pressure.

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• Heavy equipment such as backhoes or tractors
  often use hydraulics. Even airplanes flaps use
  hydraulics.

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• Pneumatic Systems use gas (usually air), but do
  not seal it. The air usually escapes somewhere
  in the device.
• High pressure air may come from a machine that
  draws in outside air and compresses it.

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• A jackhammer is a pneumatic device high
  pressured burts of air drive the chuck in and out
  of the ground! Some staple guns, nail guns and
  sandblasters use pneumatics as well.

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• In a hovercraft, pumps draw in outside air and
  pump it out of the bottom.

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• Hydraulics/Pneumatics in Body
• Respiratory System is a Pneumatic System
• Circulatory System is a hydraulic system