P4- Explaining Motion

OCR 21st Century  

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  • Created by: Abi_xx
  • Created on: 11-08-14 20:06
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  • P4- Explaining Motion
    • Forces
      • A FORCE occurs when 2 objects INTERACT
        • The forces in an INTERACTION PAIR are        1. equal in size                2. Opposite in direction and act on different objects
          • AIR RESISTANCE : Air tries to slow down a sky diver, the skydiver pushes the air out of their way (equal and opposite force)
          • GRAVITY : 2 masses are attracted to each other eg You and Earth with an equal and opposite force
          • ROCKET AND JET ENGINES : Engine pushes gas backwards and gas pushes rocket forward
      • Forces and Motion
        • ARROWS on diagrams are used to represent 1.The size of the force 2.Direction the force is acting in
          • Arrows are always draw with the tail touching the object
        • If MORE THAN 1 force acts on an object they will : 1.Add up if they are in the same direction 2.Subtract if different directions
          • The overall effect is called RESULTANT FORCE
      • There is always a DRIVING FORCE and a COUNTER FORCE
        • If the driving force is 1.< counter force = speed increase 2.Equal to the counter force = constant speed in a straight line 3.>counter force=decrease in speed
    • Kinetic Energy
      • The amount of K.E an object has depends on 1.Mass and 2.Velocity
      • K.E (Joules, J) = 1/2 x Mass (kg) x Velocity squared (m/s(squared)
    • Work and Energy
      • When work is done :     1.On an object, it gains energy 2.By an object it loses energy
      • Work done by a force (j) = Force (n) x Distance moved in direction of force (m)
        • When a force makes an objects velocity increase 1.Work is done on the object by the force      2.The object gains K.E
      • Some of the energy will be dissipated (lost) as heat
    • Gravitational Potential Energy
      • When an object is lifted above the ground 1.Work is done by the lifting force against gravity    2.The object has the potential to do work when it falls
      • Change in G.P.E (J) = Weight (N) x Vertical Height difference (M)
      • To Find G.P.E you use WEIGHT not mass

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