AQA - physics paper 2

• Force


  Any push or pull
• Types of forces

  • Contact forces (when objects are physically touching)
  • Non-contact forces (like magnetism, electrostatic forces, gravity)
• Contact forces

  • Normal contact force (pushing a door)
  • Friction
  • Air resistance
  • Tension
• Finding resultant force

  1. Technically adding the vectors

  2. If in opposite directions, one is negative

  3. If at right angles, use Pythagoras or trigonometry
• Balanced forces

  Forces add up to zero, object will not accelerate but may be moving at constant velocity
• Scalar


  Quantity with magnitude but no direction
• Vector


  Quantity with both magnitude and direction
• Scalar quantities

  • Displacement
  • Velocity
• Weight

  Force due to gravity acting on an object, calculated as mass * gravitational field strength
• Lifting an object at constant speed

  Lifting force must equal weight
• Work done

  Energy transferred by a force, calculated as force * distance moved
• Hooke's Law

  Force equals spring constant * extension, for elastic objects
• Energy stored in a spring

  Equal to 1/2 * spring constant * (extension)^2
• Moment

  Turning force, equal to force * perpendicular distance to pivot
• Pressure

  Force per unit area, calculated as force / area
• Gas pressure

  Due to collisions of gas particles with surfaces, increased by more particles, smaller volume, or higher temperature
• Altitude and pressure

  Higher altitude means lower atmospheric pressure due to fewer particles
• Speed and velocity

  Speed is scalar, velocity is vector
• Acceleration

  Rate of change of velocity, calculated as change in velocity / time
• Newton's First Law

  An object's motion is constant if there is no resultant force
• Newton's Second Law

  Force equals mass * acceleration
• Newton's Third Law

  For every action force, there is an equal and opposite reaction force
• Doubling speed

  Quadruples braking distance
• Momentum

  Mass * velocity, a vector quantity
• In a collision, total momentum is always conserved, but kinetic energy may not be
• Doubling your speed

  Quadruples your braking distance
• Kinetic energy is equal to half MV squared
• Tripling your speed

  Kinetic energy goes up by time 9
• Kinetic energy going up by time 9

  Braking distance also goes up by time 9
• Factors affecting thinking distance

  • Distractions
  • Alcohol
  • Drugs
• Factors affecting braking distance

  • Condition of brakes
  • Tires
  • Road
  • Weather
• Momentum


  Measure of how hard it is to get something to stop
• Momentum

  Mass times velocity
• Momentum is a vector
• In a collision, kinetic energy isn't always conserved but total momentum always is
• Calculating momentum before and after a collision

  1. M1 U1

  2. M2 U2

  3. M1 V1 + M2 V2
• If nothing is moving before a collision, total momentum before is zero
• Total momentum before = Total momentum after
• Recoil is an example of total momentum being conserved
• Force


  Rate of change of momentum