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# Chapter 9

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### Chapter 9

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