P4 - Explaining Motion

P4 - Explaining Motion

1. Speed

   • Speed (m/s) = Distance Traveled (m) / Time Taken (s)
   • Distance (m) = Speed (m/s) X Time Taken (s)
   • Time (s) = Distance (m) / Speed (m/s)

2. Distance-Time Graphs

   • Gradient = Speed
   • Flat sections are where it's stationary
   • The steeper the gradient, the faster it is going
   • Straight lines meaning the object is moving at a constant speed
   • A steeping curve = Acceleration
   • A leveling off curve = Deceleration
   • Speed = Gradient = Vertical / Horizontal

3. Displacement-Time Graphs

   • Displacement can be Positive or Negative
   • They show is two different objects travelling different directions from a point

4. Acceleration

   • Acceleration (m/s~2) = Change in Velocity (m/s) / Time Taken (s)
   • Change in Velocity (m/s) = Acceleration (m/s~2) X Time Taken (s)
   • Time Taken (s) = Change in Velocity (m/s) / Acceleration (m/s~2)

5. Velocity-Time Graphs

   • Gradient = Acceleration
   • Flat sections = Constant Speed
   • The steeper the gradient, the greater the acceleration or deceleration
   • Uphill sections are acceleration
   • Downhill sections are deceleration
   • Negative Velocity means the object is travelling in the opposite direction

6. Forces and Friction

   • Forces occur when two object interact
   • An object resting on a surface experiences a reaction force
   • Moving objects normally experience friction
   • Three types of Friction
     • Friction between solid surfaces which are gripping
     • Friction between solid surfaces which are sliding past each other
       • Can be reduced by adding a lubricant
     • Resistance or "Drag" from fluids

7. Acceleration

   • When a car exerts a bigger driving force than the drag counter force, the car will then accelerate.
   • The bigger the force, the greater the acceleration

8. Momentum

   • Momentum (kg m/s) = Mass (kg) X Velocity (m/s)
   • Velocity (m/s) = Momentum (kg m/s) / Mass (kg)
   • Mass (kg) = Momentum (kg m/s) / Velocity (m/s)

9. Change of Momentum

   • Change of Momentum (kg m/s) = Resultant Force (N) x Time for which the force acts (s)
   • Resultant Force (N) = Change of Momentum (kg m/s) / Time for which the force acts (s)
   • Time for which the force acts (s) = Change of Momentum (kg m/s) / Resultant Force (N)

10. Car Safety Features Reduce Forces

    • Crumple Zones
      • Increases the time taken for the car to stop
    • Air Bags
      • Slows the passenger more gradually
    • Seat Belts
      • Increases the time taken for the wearer to stop (reduces the forces acting on the chest)
    • Helmets
      • Increases the time taken for your head to come to a stop if it hits something hard

11. Work

    • When a force moves an object, it does work and energy is transferred to the object
    • Amount of energy transferred (J) = Work Done (J)

12. Work done by a force

    • Work done by a force (J) = Force (N) x Distance moved in direction of force (m)
    • Force (J) = Work done by a force (J) / Distance moved in direction of force (m)
    • Distance moved in direction of force (m) = Work done by a force (J) / Force (N)

13. Kinetic Energy

    • Kinetic Energy (J) = 1/2 x Mass (kg) x Velocity~2 ([m/s]~2)
    • Mass (kg) = 1/2 x Kinetic Energy (J) / Velocity~2 ([m/s]~2)
    • Velocity~2 ([m/s]~2) = 1/2 x Kinetic Energy (J) / Mass (kg)

14. GPE

    • Change in GPE
      • Change in GPE (J) = Weight (N) x Vertical Height Difference (m)
      • Weight (N) = Change in GPE (J) / Vertical Height Difference (m)
      • Vertical Height Difference (m) = Change in GPE (J) / Weight (N)
    • Kinetic Energy Gained - GPE Lost