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
• Force representation


  Vectors (arrows showing direction and magnitude)
• Finding resultant force


  1. Technically adding vectors (if in opposite directions, one is negative)

  2. Using Pythagoras if at right angles

  3. Using trigonometry (SOHCAHTOA)
• Balanced forces


  Forces add up to zero, object does 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 x gravitational field strength
• 1 kg of mass on Earth has a weight of 10 N
• Lifting an object at constant speed

  Upward force must equal weight
• Calculating work done


  Work done = Force x Distance moved
• Gravitational potential energy


  Mass x Gravitational field strength x Height
• Hooke's law


  Force = Spring constant x Extension
• Energy stored in a spring

  0.5 x Spring constant x (Extension)^2
• Moment


  Turning force, equal to Force x Perpendicular distance to pivot
• Balanced moments mean no turning
• Pressure


  Force per unit area, calculated as Force / Area
• Pressure in liquids


  Pressure = Depth x Density x Gravitational field strength
• Gas pressure


  Due to collisions of gas particles with surfaces, increased by more particles, smaller volume, higher temperature
• Pressure decreases with increasing altitude due to lower atmospheric density
• Velocity


  Speed with direction, can be positive or negative
• Calculating speed and velocity

  Speed = Distance / Time

  Velocity = Displacement / Time
• Acceleration


  Change in velocity over time, measured in m/s^2
• Acceleration due to gravity

  9.8 m/s^2 downwards
• Using velocity-time graphs


  Gradient = Acceleration

  Area = Displacement
• Newton's first law


  An object at rest stays at rest, an object in motion stays in motion, unless acted on by a resultant force
• Newton's second law


  Force = Mass x Acceleration
• Proving Newton's second law

  Use a trolley on a track, measure acceleration with light gates, plot force vs acceleration graph
• 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
• Momentum is conserved in collisions, 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
• Tripling your speed


  Braking distance also goes up by time 9