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Welcome to Physics lesson… FORCE AND MOTION Chapter 2 Prepared by Gayah Normahzura Bt Khaizan

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Observe the animations below.. 1 2

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 1 t = 0 v = 0 v = The car is…. t = 2 s t s = 0 s = 50 m

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 2 t t = 0 v = 30m/s t = 3 s v = 0 The car is…. s = 0 s = 50 m

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The objective of today’s lesson is: <ul><li>Define acceleration and deceleration and state that : </li></ul><ul><li>a = v – u </li></ul><ul><li> t </li></ul>

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Previous Lesson.. <ul><li>Distance and displacement </li></ul><ul><li>Speed and velocity </li></ul><ul><li>Average speed, </li></ul><ul><li>Average velocity, </li></ul><ul><li>The SI unit for speed and velocity is __ __. </li></ul>v = ? v = ?

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Previous Lesson.. <ul><li>Distance and displacement </li></ul><ul><li>Speed and velocity </li></ul><ul><li>Average speed, </li></ul><ul><li>Average velocity, </li></ul><ul><li>The SI unit for speed and velocity is m/s. </li></ul>v = s t v = s t

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What will you learn now? <ul><li>Acceleration and deceleration </li></ul>Definition Equation

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Activity…

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Instruction.. <ul><li>Discuss in group </li></ul><ul><li>A car accelerates from rest to 15m/s in 15 s. </li></ul><ul><li>Plot a graph of velocity versus time with given information. </li></ul>Q1 15 15 10 10 5 5 0 0 Velocity, v (m/s) Time, t (s)

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v = 0 v = 15m/s Time & Velocity change Time, t increase Velocity, v increase m/s (s) 15 15 10 10 5 5 0 0 Velocity, v (m/s) Time, t (s)

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Definition <ul><li>Acceleration  is defined as the rate of change of velocity. </li></ul><ul><li>The units for acceleration is m/s² </li></ul>Equation Acceleration= change of velocity time taken for the change a = v - u t

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Instruction.. <ul><li>Discuss in group </li></ul><ul><li>Plot a graph of velocity versus time with given information </li></ul>Q2 0 6 2 4 4 2 6 0 Velocity, v (m/s) Time, t (s)

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v = 6m/s v = 0 m/s (s) 0 6 2 4 4 2 6 0 Velocity, v (m/s) Time, t (s)

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a = v – u t v u a t

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a  acceleration v u t  Final velocity  Initial velocity  Final velocity

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EXERCISE <ul><li>(1) An object moves from rest with a uniform acceleration of 2 ms -2 .What is the velocity of the object after 30 s? </li></ul>

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Answer….. <ul><li>Solution… </li></ul><ul><li>u = 0 t = 30 s </li></ul><ul><li>a = 2 ms -2 </li></ul><ul><li>a = v- u </li></ul><ul><li>t </li></ul><ul><li>v = u + at </li></ul><ul><li>= o + (2 x 30) </li></ul><ul><li>= 60 ms -1 </li></ul>

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<ul><li>(2) A car increases its velocity steadily from </li></ul><ul><li>72 km h -1 to 108km h -1 in 5 s. What is its </li></ul><ul><li>acceleration in ms -2 ? </li></ul>

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Answer…… <ul><li>Solution….. </li></ul><ul><li>u = 72km h -1 v = 108 km h -1 </li></ul><ul><li>= 72 x 1 000 = 108 x 1 000 m s -1 </li></ul><ul><li>60 x 60 60 x 60 </li></ul><ul><li>= 20 m s -1 = 30 m s -1 </li></ul><ul><li>t = 5 s </li></ul><ul><li>Acceleration, a = v – u = 30 - 20 m s -1 </li></ul><ul><ul><ul><ul><ul><li> t 5 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>= 2 m s -2 </li></ul></ul></ul></ul></ul><ul><li> </li></ul>m s -1