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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