AQA Physics Spec B Unit 2

general overview of all topics in AQA B unit 2 Physics.

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Keeping Balanced

  • Objects in equilibrium will either be at rest or moving with a constant speed.
  • An unbalanced force means the object will accelerate.
  • For a static object, the horizontal and vertical forces must cancel out.
  • Add vectors 'Tip to Tail' when drawing a vector triangle to analyse objects in equilibrium.
  • For an object on a slope, e.g Skier, we can resolve weight into components parallel and perpendicular to the slope.
  • Parallel= Wcos theta
  • Perpendicular= Wsin theta
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Velocity and Acceleration

  • Velocity and Acceleration are Vector quantities (meaning they have a magnitude and a direction)
  • v= change in displacement / change in time
  • A= change in velocity/ change in time
  • Distance-Time graph, Gradient = Acceleration
  • Speed-Time graph, Area below line= Distance, Gradient = Acceleration.
  • Equations of Motion apply to objects experiencing a constant acceleration e.g gravity.
  • Stopping Distance = thinking distance+ braking distance.
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Changing Forces

  • Perpendicular vectors have no effect on each other- they are treated independantly.
  • A Projectile is an object subjected to the acceleration of free fall.
  • The horizontal motion is one of constant velocity ( thus acceleration is always zero)
  • Drag- resists movement of an object as it moves through a fluid. e.g air.
  • As an obect accelerates, so does the Drag force upon them.
  • When an obect is falling but drag is significant, F=M X A becomes F= M(g-A) where g= gravitational force.
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Energy Changes

  • Work is done when a force causes an object to move.
  • W= Fs cos theta.
  • Gravitational Potential energy is when an object is raised.
  • Elastic potential energy is when an object is stretched/compressed.
  • Kinetic energy is energy of an object due to its motion.
  • Power is the rate of energy transfer with time.
  • when a sprinter runs, the energy transfer is Chemical energy to Kinetic Energy to Thermal and Sound Energy.
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Stopping Safely

  • Momentum is a vector quantity. p= mv (p=momentum, m=mass of object, v= velocity of object)
  • In an isolated system, total initial momentum= total final momentum.
  • When the system is subjected to a force or 'Impulse' (Fx change in t) momentum is not conserved.
  • Cars have crumple zones in order to increase the time over which a collision takes place, thus reducing the force on the driver, since mv=Fx change in t.
  • Seat belts and air bags use the same concept.
  • the longer an object is in contact with a force, the greater the momentum of the object when it is released. (e.g tennis racquet and ball)
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