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 force, 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, with forces in opposite directions being negative

  2. Using Pythagoras or trigonometry if forces are at right angles
• Balanced forces


  Forces that add up to zero, meaning the object will not accelerate
• Scalar


  A quantity with magnitude but no direction
• Vector


  A quantity with both magnitude and direction
• Scalar quantities


  • Displacement, velocity, weight
• Vector quantities


  • Distance, speed, force
• Weight


  The force due to gravity acting on an object, calculated as mass x gravitational field strength
• 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
• 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


  A turning force, equal to force x perpendicular distance to pivot
• 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
• Velocity


  Speed with direction, measured in m/s
• Acceleration


  Rate of change of velocity, measured in m/s^2
• Newton's First Law


  An object's motion is constant unless acted on by a resultant force
• 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, with light gates to measure acceleration

  2. Plot a graph of force vs acceleration, the gradient gives the total mass
• Newton's Third Law


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

  Thinking distance doubles when speed doubles, but braking distance quadruples
• Momentum


  Mass x 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, so it can be negative
• 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