Physics P3 Forces and Motion

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  • Created by: A.P
  • Created on: 19-01-13 17:11
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  • Forces and Motion
    • Forces, Mass and Acceleration
      • If the forces acting on an object are balanced, it's at rest or has a constant speed. If the forces acting on an object are unbalanced, it speeds up or slows down.
      • The unit of force in the newton (N).
      • force = mass x acceleration
        • Where F = unbalanced force in N, m = mass in kg and a = acceleration in m/s2
      • The equation f=ma is used to find mass or acceleration if the resultant force is known.
    • Car Safety
      • Reaction time, and therefore thinking distance, may increase if a driver is...
        • ...tired, under the influence of alcohol or other drugs, travelling faster or distracted (lacking concentration).
      • Braking distance may increase if...
        • ...thre road conditions are poor, e.g. icy, the car has not been properly maintained, e.g. worn brakes, or the speed is increased.
      • For safe driving, it is important to be able to stop safely.
        • Keep an appropriate distance from the car in front.
          • Have different speed limits fro different types of road and locations.
            • Slow down when road conditions are poor.
      • Factors affecting breaking distance are:
        • The greater the mass of a vehicle the greater its braking distance.
          • The greater the speed of a vehicle the greater its braking distance.
            • When the brakes are applied the brake pads are pushed against the disc. This creates a large friction force that slows the car down. Worn brakes reduce the friction force, increasing the braking distance.
              • Worn tyres with very little tread reduce the grip of the wheels on a slippery road, leading to skidding and an increase in distance.
                • Increased braking force reduces the stopping distances.
      • Thinking distance increases linearly with speed.
        • Braking distance increases as a squared relationship, e.g. the braking distance at 60mph is nine times the braking distance at 20mph.
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