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
• Resultant force


  The net force acting on an object when multiple forces are present
• Finding resultant force


  1. Technically adding the vectors

  2. If forces are in opposite directions, one is negative

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


  Forces that add up to zero, meaning the object will not accelerate
• Balanced forces mean the object stays at a constant velocity, which could be 0 m/s
• Scalar


  A quantity with magnitude but no direction
• Vector


  A quantity with both magnitude and direction
• Weight


  The force due to gravity acting on an object, calculated as mass x gravitational field strength
• 1 kg of mass on Earth has a weight of 10 N
• When lifting an object at constant speed

  The upward force must equal the weight of the object
• Work done


  Energy transferred by a force, calculated as force x distance moved
• Gravitational potential energy


  Energy gained when an object is lifted, calculated as mass x gravitational field strength x height
• Hooke's law


  Force = spring constant x extension, for elastic objects
• Moment


  A turning force, calculated as force x 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 adding more gas, reducing volume, or increasing temperature
• Atmospheric pressure decreases with altitude due to fewer gas particles
• Speed and velocity


  Speed is a scalar, velocity is a vector
• Acceleration


  Rate of change of velocity, calculated as change in velocity / time
• Acceleration due to gravity is 9.8 m/s^2
• Newton's first law


  An object's motion is constant if the net force is zero
• Newton's second law


  Force = mass x acceleration
• Proving Newton's second law

  1. Use a trolley on a track, pulled by weights over a pulley

  2. Measure acceleration using light gates

  3. Plot force vs acceleration graph, should be a straight line through the origin
• Newton's third law


  For every action force, there is an equal and opposite reaction force
• Thinking distance


  Distance travelled before reacting to a hazard
• Braking distance


  Distance travelled while braking
• Doubling speed


  Quadruples braking distance
• Momentum


  Mass x velocity, a vector quantity
• In a collision, total momentum is always conserved, but kinetic energy is not always conserved
• 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, so negative velocity means negative momentum