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
• Representing forces


  Vectors - an arrow that shows the direction and magnitude of the force
• Finding resultant force


  1. Technically adding the vectors

  2. If forces are in opposite directions, one must be negative

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


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


  Quantity with magnitude but no direction
• Vector


  Quantity with both magnitude and direction
• Scalar quantities


  • Distance, speed, mass, weight
• Vector quantities


  • Displacement, velocity, acceleration, force
• 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

  Lifting 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
• Energy stored in a spring

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


  Turning force, equal to force x perpendicular distance to pivot
• Balanced moments mean an object will not turn
• 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 adding more gas, reducing volume, or increasing temperature
• Atmospheric pressure decreases with increasing altitude
• Speed and velocity


  Speed is scalar, velocity is vector
• Acceleration


  Rate of change of velocity, calculated as change in velocity / time
• Acceleration due to gravity is 9.8 m/s^2
• Equations of motion


  Relate displacement, initial velocity, final velocity, acceleration, and time
• Newton's first law


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


  Resultant force = mass x 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 stimulus, proportional to speed
• Braking distance


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