Mechanics

• The four types of motion are:

  • linear
  • rotary
  • reciprocating
  • oscillating
• Name the motion and give an example:

  A) Linear

  B) Train

  
• Name the the motion and give an example:

  A) Rotarty

  B) Wheels

  
• Name the motion and give an example

  A) Reciprocating

  B) Water pump

  
• Name the motion and give an example

  A) Oscillating

  B) Clock pendulum

  
• There are 3 types of levers:

  First order

  Second order

  Third order
• 1st order lever:

  A) LOAD

  B) FULCRUM

  C) EFFORT

  
• 2nd order lever

  A) EFFORT

  B) LOAD

  C) FULCRUM

  
• 3rd order lever

  A) FULCRUM

  B) EFFORT

  C) LOAD

  
• Fill in the blanks for the levers equation:

  A) Load

  B) Mechanical advantage

  C) Effort

  
• Simple linkages change the direction of motion and the amount of force. In the exam, you will likely have motion linkages to work out angles on the pivots
• Name the linkage and give an example

  A) Reverse motion

  B) Indoor washing lines

  
• Name the linkage and give an example

  A) Parallel motion

  B) Tool storage box

  
• Name the linkage and give an example

  A) Bell crank

  B) Bike brakes

  
• Name the linkage

  A) Crank and slider

  
• A spark plug is an example of a crank and slider linkage
• Name the linkage

  A) Treadle

  
• A windscreen wiper is an example of a treadle linkage
• A reverse motion linkage is an alternate angle

  
• In two intersecting lines, the opposite angles are equal

  
• 2 parallel lines joined by one intersecting line forms corresponding angles

  
• Mechanical devices


  Can change one form of force to another. All moving parts work on some sort of mechanism.
• Cams and followers


  • Shaped part on a pivot point that converts reciprocating motion to rotary motion
  • Has two main parts: a cam and a follower
• Cam


  A wheel attached to a crankshaft that rotates
• Follower


  A bar that follows a cam around its circumference, touching the cam and following the shape, moving up and down
• Common cam shapes


  • Circular
  • Pear
  • Snail or drop
  • Heart-shaped or constant velocity
• Circular cams


  • Use an off-centre pivot to cause the follower to move up and down, with a reasonably large amount of rise and fall
  • Can be seen in pistons, for example on steam engines
• Pear cams


  • Remain stationary for half a turn then gently rise and fall
  • Used to make carousel horses rise and fall
• Snail or drop cams

  • Cause the follower to remain stationary for half a turn before gently rising and suddenly falling
  • Can only work by rotating in one direction
  • Used on production lines to make regular holes or cuts in an item as it rotates and drops at regular intervals
• Heart-shaped or constant velocity cams


  • Have a shape similar to a heart
  • The follower rises and falls steadily with uniform velocity
  • There is no stationary period
• Types of followers


  • Flat
  • Point or knife
  • Roller
• Flat followers


  • Have a flat bottom that sits on the cam
  • Cope well under load but aren't very accurate and have a lot of friction
• Point or knife followers


  • Have a narrow point that sits on the cam
  • Are very accurate and low friction but are quick to wear away the pointed edge
• Roller followers


  • Have a roller such as a ball bearing attached to the bottom
  • Are accurate, low on friction and can withstand load, but are more costly to produce
• Gear


  A wheel with teeth that can change the speed of a mechanism
• Teeth


  Projecting part of a component such as a gear around the outside
• Gear trains


  • Two or more gears interlocking together
  • Can transfer motion from one place to another
  • Can change the direction or the speed of movement
  • Gears can withstand greater force enabling them to move large items
• Drive gear


  The starting gear in a gear train that causes all other movement
• Driven gear


  Transfers motion from the drive gear
• Gear ratio


  The number of turns the driven gear will make for every turn of the drive gear