Section 2

• linear motion


  motion in a straight line eg a train

  
• rotary motion


  motion in a circular point around a central pivot point eg children's roundabout

  
• reciprocating movement


  A back and forth movement in a straight line eg bicycle pump

  
• OSCILLATING MOTION


  Oscillating motion occurs when an object swings left and then right (or vise-versa), from a fixed point. A very good example of this is a classic pendulum clock

  
• Mechanical Advantage (MA)


  the force that comes out is more than the force put in
• MA

  Load/ effort
• the two parts to a lever


  bar, fulcrum (pivot)
• why use a lever

  the force of effort can be reduced for the same load
• what factors to consider in MA

  the effort: input force

  the load: output force

  position of the fulcrum (pivot)
• when will MA increase?

  the load is closer to the fulcrum

  the effort is further away from the fulcrum
• class 1 lever


  fulcrum in the middle eg seesaw

  
• class 2 lever


  Load in the middle eg wheelbarrow

  
• class 3 lever


  effort in the middle eg tweezers

  
• when would you use a class 3 lever


  when you want the force coming out to be less than the force coming in
• linkage


  group of rigid links or lever connected together to create a range of movement
• what are linkages used for?

  to change the type, direction and/ or force of a motion
• bell crank linkage


  Changes the direction of the input motion through 90ᵒ.

  can be used to change or horizontal movement to a vertical one

  
• Parallel motion linkage


  the push/ pull linkage keeps the direction of motion the same for the input and the output

  
• reverse motion linkage


  reverses the motion of the input and giving an opposite output motion

  
• what is the use or cams and followers

  change a rotary motion into a reciprocating motion
• Cams and followers


  a shaped piece of material with a hole for a cam shaft.

  The cam is rotated with a cam shaft.

  A follower rests on the cam and travels up and down as the cam is rotated.

  A dwell is when the follower does not move even though the cam is still rotating.

  
• Circular cam


  This is a circular disk with an off centre hole.

  When the cam is rotated the follower rises and falls smoothly.
• Pear shaped cam


  This is a pear or egg shaped cam with a hole.

  When the cam is rotated the follower rises and falls quickly and then dwells for a short time.

  
• Snail cam

  This is the shape of a snail shell with a hole.

  When the cam is rotated the follower rises steadily and then suddenly drops.

  Only works in one direction.

  
• Knife edge follower

  Good for precision.

  Not good for heavy loads.

  Low friction - however tip wears easily.

  
• Flat follower

  Not good for precision.

  Good for heavy loads.

  Large flat surface creates friction.

  
• Roller follower


  Some precision.

  Good for heavy loads.

  Roller rotates reducing friction.

  
• Simple gear trains


  Gear trains can be used to change the speed, direction and/or power of the output motion.

  Simple gear trains consist of two gears.

  The gears may be different sizes.

  
• Driver gear


  The driver gear (A) is attached to a motor.

  The driver gear (A) rotates, rotating the driven gear (B).

  
  

  If gear A is a larger gear then gear B will rotate faster.

  
• Pulley systems


  Pulley systems can be used to change the speed, direction and/or power of the output motion.

  A simple pulley system is made up of two pulley wheels and a belt.

  The pulley wheels may be different sizes.

  
  

  The driver pulley wheel (A) is attached to a motor.

  The driver pulley wheel (A) rotates turning the belt which turns the driven gear (B).

  A simple pulley system can be used to help lift a heavy load.

  
• Gear ration=


  Teeth on gear A/Teeth on gear B
• Systems diagrams tend to be drawn using:


  Flow charts
• Name the three types of mechanical switches.

  Pressure switch

  Push to make switch

  Toggle switch
• What kind of mechanical switch is used for light switches?

  Toggle switch
• What are Integrated circuits (IC) and microcontrollers?

  They are chips

  They are used to process the inputs and control outputs

  They can be pre-programmed or programmed by the designer
• integrated circuits (ICs)


  most processes are controlled by these and can perform tasks
• microcontoller


  a modern IC that can perform multiple tasks and applications
• analogue signal


  a continuous signal with an infinite range of values between minimum and maximum points.

  - would be produced by a thermistor as it changes from hot to cold

  - or light dependant resistor sensing change from dark to light

  
• digital signal


  either on or off, represented by 1 and 0 e.g. a switch

  
• peripheral interface controllers (PICs)


  also known as a microcontroller, programmed by sending a code from a controller to the IC using a cable e.g. USBmono