Science 8 | Unit D | Test Study

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  • The formula of Mechanical Advantage is MA = Force out/Force in
  • Mechanical Advantage (MA) also known as force ratio or mechanical ratio.
  • Mechanical Advantage (AKA force ratio or mechanical ratio)
    • The amount by which a machine can concentrate force
    ○ The force applied to the machine is the input force
    ○ The force the machine applies to the object is the output force
  • Speed Ratio
    • a measure of how the speed of the object is affected by the machine
    ○ The distance the input force moves is the input distance (ID)
    ○ The distance the load is moved by the machine is the output distance (OD)
  • Work
    𝑤𝑜𝑟𝑘 𝑖𝑠 𝑑𝑜𝑛𝑒 𝑤h𝑒𝑛 𝑎 𝑓𝑜𝑟𝑐𝑒 𝑎𝑐𝑡𝑠 𝑜𝑛 𝑎𝑛 𝑜𝑏𝑗𝑒𝑐𝑡 𝑡𝑜 𝑚𝑎𝑘𝑒 𝑖𝑡 𝑚𝑜𝑣𝑒.
    Work = Force x Distance
  • Work input equals to work output WITHOUT friction. In real life, work in ≠ work out because energy is lost due to friction.
  • ○ F is force measured in Newtons (N)
    ○ d is distance measured in metres (m)
    ○ W is measured in Nm or Joules (J)
  • Efficiency
    a measure of how well a machine or device uses energy.
    Efficiency = Work out/Work in * 100
  • MA vs SR
    • MA is affected by friction, while SR is not
    • Big MA = Big SR
    • Small MA = Small SR
  • Work IN vs Work OUT
    • Work in ≠ Work out because of energy lost by friction
    Any machines ‘loses’ some energy as it operates
    ○ Example: energy lost as heat due to friction
    ○ It is ‘lost’ because the energy is not being used to complete the machine’s task
    ● A complex machine is less efficient because all of its subsystems are affected by friction and other factors
  • Work cont.
    ○ ○ The object has to move in order for work to be done
    ■ (holding a heavy box at a consistent height may feel like you're doing work, but
    scientifically you’re not)
    ● The amount of work done depends on the amount of force applied to the object, and the
    𝑇h𝑒 𝑜𝑢𝑡𝑝𝑢𝑡 𝑓𝑜𝑟𝑐𝑒 𝑖𝑠 𝑙𝑒𝑠𝑠 𝑡h𝑎𝑛 𝑡h𝑒 𝑖𝑛𝑝𝑢𝑡 𝑓𝑜𝑟𝑐𝑒 𝑏𝑢𝑡 𝑡h𝑎𝑡 𝑡h𝑒 𝑖𝑛𝑝𝑢𝑡 𝑑𝑒𝑣𝑖𝑐𝑒 𝑚𝑜𝑣𝑒𝑑
    𝑙𝑒𝑠𝑠 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡h𝑎𝑛 𝑡h𝑒 𝑜𝑢𝑡𝑝𝑢𝑡 𝑑𝑒𝑣𝑖𝑐𝑒.
    distance that the object is moved in the direction of the applied force
  • Hydraulic System
    a system that uses a liquid under pressure to move loads
    ○ increases the MA of a lever
  • Hydraulic System cont.
    ● Hydraulic systems have large mechanical advantages
    ● Recall: a fluid transmits pressure equally
    ● A small force on the small (input) piston creates a pressure .
  • MA has a cost
    Just like with levers or ramps, to achieve the greater MA of a hydraulic system, you put move the input piston further than the output piston
  • Pressure & MA
    ● That pressure moves throughout the system, and presses on the large piston
    ● With the same pressure acting on a larger space, the force is then increased
  • Pressure and MA
    ● The pressure throughout the whole system is the same, therefore the ratio of force/area must also be the same
    Area of large piston = 100 cm
  • Pressure and MA
    ● The pressure throughout the whole system is the same, therefore the ratio of force/area must also be the same
  • Pressure in = Pressure out, with no friction
  • Pressure: a measure of the amount of force applied to a given area (p=F/A)
    ○ P is pressure measured in Pa
    ○ F is force measured in N
    ○ A is area measured in m2
  • Pascal’s Law: pressure applied to an enclosed (sealed) fluid transmitted equally in all directions throughout the fluid
    ○ Application: hydraulic jacks
  • Efficiency: a measure of how well a machine or device uses energy.
    ○ A ratio of MA (actual) / SR (or the ideal MA)
  • Efficiency: a measure of how well a machine or device uses energy.
    ○ A ratio of MA (actual) / SR (or the ideal MA)
    ● Any machines ‘loses’ some energy as it operates
    ○ Energy lost as heat due to friction
    ○ ‘Lost’ because the energy is not being used to
    complete the machine’s task
    E.g. A complex machine is less efficient than simple
    machines, because its subsystems are affected by friction.
  • The formula for efficiency is efficiency = MA/SR * 100
    The formula for efficiency is percentage is efficiency (%) MA/SR * 100 = 2/3 * 100 = 66.67%
  • Effectiveness: A machine or device successfully achieves a desired result
  • Function vs Design
    Function — The function of a device is what it is supposed to do.
    Design — The design of the device is the physical form that it takes to make it usable.
    The design must suit the function effectively and efficiently.
  • Machine
    • Helps people use energy more effectively
    • A device that helps us do work
  • The 6 simple machines are:
    • Inclined plane
    • Lever
    • Pulley
    • Screw
    • Wedge
    • Wheel & axle
  • Inclined plane
    ● An inclined plane (or ramp) makes it possible to lift heavy objects
    ○ Consider lifting a heavy box straight up onto a table or using a ramp
    Advantages: Reduce the force needed to carry out a task
    Disadvantages:
    You must exert the force over a larger distance
    Only useful for small inclines
  • Wedge
    Similar shape to an inclined plane, but used differently
    ● The wedge machine is forced into an object to split them apart
    Advantages: Increases the force you apply to an object
    Disadvantages:
    • You must move the wedge a greater distance than the split it makes
    • Only works to push things apart 
  • Screw
    ● A cylinder with a groove cut in a spiral on the slide
    ● Helps you penetrate into objects
    ● Can also convert rotational (turning) motion into linear motion
    (straight line)
    Advantages: Can penetrate materials with very little force
    Disadvantages: The work gets done quite slowly
  • Pulley
    ● A pulley consists of a wire/ rope/ cable moving on a wheel
    ● They can be made of one wheel or many, and the wheel can be fixed in place or moveable
    Advantages: Help you lift larger loads than you could lift on your own
    Disadvantages:
    Generally will have to move a farther distance
  • Wheel and Axle
    ● A wheel and axle is a combination of two different wheels of different diameter that turn together
    ● The longer motion in the wheel produces a shorter, but more powerful motion in the axle
    Advantages:
    Increases the force of movement
    Helps you move faster than you otherwise could
    Disadvantages:
    Have to turn the larger wheel a greater distance to apply the force.
  • Effects of Simple Machines
    A simple machine can increase the
    force that you apply or change the direction of the force, but the force you apply has to move farther than the load does
  • Levers
    ● A lever is a rigid bar that can rotate around a fixed point called a fulcrum
    ● There are 3 classes of levers (What’s in the middle?):
    ○ 1st Class lever: the fulcrum is between the load and
    the effort (E-F-L)
    ■ Example: See-saw
    ○ 2nd class lever: the load is between the effort and fulcrum (E-L-F)
    ■ Example: Wheelbarrow
    ○ 3rd class lever: the effort is between the load and
    fulcrum (L-E-F)
    ■ Example: Fishing rod, baseball bat
    Advantages:
    Reduced force needed to carry out a task (Can move heavier loads than without it)
    Disadvantages:
    You must move a greater distance than the load does
  • Complex Machines: Machines that are made up of several simple machines working together
    ○ most machines we use today are complex machines
  • Subsystems: groups of parts in a larger system that have a specific function.
    ○ Example: the parts of a bike responsible for braking
  • Linkages: the part of a machine that transfers energy from where it is inputted to where it is needed
    ○ In a bike, this is the chain that connects the pedals to the tires
  • Transmissions: a special type of linkage used in machines that have much larger loads. They contain many gears to help transfer the energy to the wheels.
    ○ The gears allow the operator to apply a large force to move objects slowly, or a small force to move objects quickly
  • Gears
    ● Gears have a pair of wheels with interlocking teeth
    ● When they rotate together, one gearwheel transfers turning
    motion and force to the other
    ○ Larger gears rotate more slowly than smaller ones
    ○ Larger gears rotate with more force
    ● Gears can be used to increase/decrease speed in a machine
  • What are Systems?
    • Sets of interacting or interdependent components