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 vectors

  2. If 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
• 1 kg of mass on Earth has a weight of 10 Newtons
• Lifting an object upwards at constant speed


  Lifting force must equal the weight
• Work done


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


  Energy gained when an object is lifted, calculated as mass * gravitational field strength * height
• 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
• Gears are an application of moments
• Pressure


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


  Pressure = depth * density * gravitational field strength
• Gas pressure


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


  Speed with direction, measured in m/s
• Acceleration


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


  An object's motion is constant if there is no resultant force
• Newton's second law


  Force = mass * acceleration
• 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, proportional to speed
• Braking distance


  Distance travelled while braking, proportional to speed^2
• Momentum


  Mass * velocity, a vector quantity
• Total momentum is conserved in collisions
• 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
• 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