Paper 2 - AQA Physics

• Vector


  Quantity with both magnitude and direction
• Scalar


  Quantity with only magnitude
• Examples of scalars


  • Speed
  • Distance
  • Time
  • Mass
  • Energy

  
• Examples of vectors


  • Velocity
  • Displacement
  • Acceleration
  • Force
  • Momentum
• Scalars cannot be negative, but vectors can be, as a certain direction is positive
• Displacement is 0 at the height of a cliff, above the cliff the ball has positive displacement, and below the cliff top the ball has negative displacement
• In long answer questions, you may be able to decide where the "0" point of a vector may lie
• Speed


  Velocity when given a direction

  
• A car travelling round a roundabout at constant speed has a constantly changing velocity, therefore it is accelerating
• Vectors


  Can be represented by arrows, with their size/length representing the vector magnitude
• Types of forces


  • Non-contact (electrostatic, gravitational attraction)
  • Contact (normal contact force, friction)
• Gravitational field


  All matter has a gravitational field, and attracts all other matter. The larger the mass, the stronger the field, the greater the attraction
• Weight


  The force exerted on a mass by the gravitational field, in Newtons. Weight = mass x gravitational field strength
• On Earth, the gravitational field strength, g, is 9.8
• The acceleration in free fall is due to gravity, and is the same as g, i.e. 10m/s^2
• The weight of an object is considered to act at the object's centre of mass
• Resultant force


  A single force representing the sum of all the forces acting on an object
• Skydiver example


  1. Initially, only weight acts

  2. As he falls, air resistance increases, resultant force decreases

  3. Eventually air resistance equals weight, so no resultant force and he reaches terminal velocity
• Free body diagram


  Shows the forces (and their directions) acting on an object
• Resolving forces


  A force F at angle θ to the ground can be resolved parallel and perpendicular to the ground using Pythagoras' Theorem

  
• Work


  Work Done = Force x Distance
• One joule of work is done when a force of one newton causes a displacement of one metre
• Work done against frictional forces causes a rise in temperature of the object
• Deformation


  Changing the shape of an object
• Types of deformation


  • Elastic (object returns to original shape)
  • Plastic (object does not return to original shape)

  
• Hooke's Law


  The extension of an elastic object is directly proportional to the force applied, provided the limit of proportionality is not exceeded

  
• Work done on a spring

  Work Done = 1/2 kx^2, where k is the spring constant and x is the extension
• Moment of a force


  Moment = Force x Perpendicular distance from pivot
• Equilibrium is when the sum of anticlockwise moments equals the sum of clockwise moments
• Gears


  • Can change speed, force or direction by rotation
  • If connected to a smaller gear, the second gear will turn faster but with less force, in the opposite direction
  • If connected to a larger gear, the second gear will turn slower but with more force, in the opposite direction
• Pressure


  Pressure = Force/Area
• Pressure in a fluid

  Pressure in a liquid varies with depth and density, leading to an upwards buoyancy force
• The atmosphere gets less dense with increasing altitude
• The weight of the air is the force which causes atmospheric pressure
• Upthrust


  A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface, creating a resultant force upwards
• Earth's Atmosphere


  • A thin layer (relative to size of the earth) of air around the Earth
  • The atmosphere gets less dense with increasing altitude
• The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth. The atmosphere gets less dense with increasing altitude.
• Idealised Assumptions, for a simple model of the atmosphere

  • Isothermal, so it is all at the same temperature
  • Transparent to solar radiation
  • Opaque to terrestrial radiation
• Distance


  How far an object moves, does not involve direction, a scalar quantity

  
• Displacement


  Includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line, a vector quantity