Force, Motion and Energy

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  • Forces, Motion and Energy
    • Resultant Forces- "overall force"
      • E.g Car engine moving car left. Air resistance moving right. The difference = resultant force
      • Resultant force not 0= accelerating or decelerating
      • Resultant force 0 = stationary or steady speed
    • Distance Time Graphs
      • Steeper gradient= faster speed
      • Flat line (no gradient) = stationary
      • Calculating speed from distance time graph (2 methods)
        • Speed= distance / time
          • eg 10m in 20 secs. Speed = 10/20. Speed = 0.5 m/s
          • Units of speed = m/s
        • Gradient method. Difference in y / difference in x
    • Velocity Time Graphs
      • Acceleration = (final velocity - initial velocity)/time
        • acceleration = m/s^(2)
        • eg A car goes from rest to 30m/s in 5 seconds
          • (30-0)/5 = 6m/s^(2)
      • Analyzing graph
        • Steeper gradient = greater acceleration
        • Flat line= steady velocity
        • Negative gradient= deceleration
      • Calculating acceleration from velocity time graphs;
        • Difference in y/ difference in x
      • Calculating distance travelled
        • Area bellow the graph. Units in m
    • Calculating Acceleration: (2 formulas- pick most suitable)
      • Acceleration= (final velocity-initial velocity)/time
      • Acceleration= Force (resultant force)/mass
    • Terminal Velocity
      • When speed increases, air resistance increases.
      • 1) Person falls out of plane. The force of weight (mass x gravity) is greater than the force of air resistance. = acceleration towards earth
        • 2) As speed increases, air resistance increases. till forces are balanced= steady speed= TERMINAL VELOCITY
          • 3) Parachute opens. Person slows down (decelerates) because air resistance increases
            • 4) Forces Balance eventually= TERMINAL VELOCITY
    • Forces on Elastic Objects
      • Work done= Energy Transferred
      • Hookes Law simplified "The more force applied, the more and elastic object will stretch provided you do  not pass the limit of proportionality"
        • Force= Spring constant x extension
          • Force=( N). Spring constant =(N/m). Extension= (m)

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