memorise

• | terminal velocity

  1. initially, weight is greater than air resistance
  2. resultant force is greater than air resistance so it accelerates downwards
  3. speed increases so does air resistance
  4. eventually, weight is same as air resistance
  5. no overall force so no more acceleration = terminal velocity
• stiffer springs experience less extension & deformation
• 1. current flows in metal wire
  2. creating a magnetic field
• | motor effect

  1. current flows through a wire
  2. created a magnetic field in the wire
  3. this field interacts with field of permanent magnet
  4. creates a force on wire which makes it move
• | DC motor

  1. coil is in magnetic field
  2. forces act on each arm of the coil
  3. current is flowing in opposite directions in each arm
  4. each arm feels opposite force
  5. split ring commutator swaps contacts every half turn
  6. this swaps current in each arm, ensuring motor turns in same direction
• split ring commutator: after half turn, contacts swap