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Chapter 9
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Chapter 9

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Transcript

  • 1. Forces Change Velocities
    • How do forces affect the velocity of objects?
  • 2. We will find out
    • How to calculate energy transfers from potential energy to kinetic energy.
    • Equate work done in decelerating to rest with initial kinetic energy.
    • Apply these ideas to situations in which vehicles and passengers are accelerated or decelerated.
    • Understand and use the principle of conservation of energy (as applied to mechanical energy).
    • How to Use the Equations
    • work done = force x distance moved in direction of force.
    • potential energy = mgh
    • power = work done/ time taken = rate of energy transfer
    • power = force x velocity
    • efficiency = (useful energy transferred / total work done) x 100%
  • 3. Acceleration
    • Acceleration is
    • Change in Velocity / Time Taken
    • But how does the force affect it?
    • The mass of the object?
    • Force = Mass x Acceleration
  • 4. Energy changes
    • Use the equations below to work through the questions on sheet
      • TAP 214-2: Along the Flat and up the Hill
  • 5. Gravitational Field
    • Gravity is proportional to mass
    • It acts on all masses
    • Gravitational field Strength and Acceleration due to Gravity are the same thing!
    • The units are both m/s 2 and N/Kg
    • Can you derive it from the equation:
    • F = ma?
  • 6. Gravitational Field
    • Gravity is proportional to mass
    • It acts on all masses
    • ‘ Gravitational field Strength’ and ‘Acceleration due to Gravity’ are the same thing!
    • The units are either m/s 2 or N/Kg
    • Can you derive it from the equation:
    • F = ma ?
    • N = Kg x a therefore a = N/Kg
  • 7. Energy Changes
    • Potential Energy = mgh
    • Kinetic energy = ½ m v 2
    • If potential energy is converted to kinetic, how does v vary with the change in h?
    • mgh = ½ m v 2 therefore gh = 1/2 v 2
    • Therefore v 2 = 2gh

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