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Kinematics Vector and Scalar Definitions Scalar: a physical quantity that can be defined by magnitude (size) only. Vector: a physical quantity that can be defined by magnitude and direction. Scalar examples: distance, time, mass, speed, energy. Vector examples: displacement, acceleration, velocity, force, momentum. NOTES p.1

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Distance and Displacement A walker takes the following path (green line). N S EW The total distance walked is shown in green. The total displacement is shown in red as a straight line from start to finish with magnitude, x, in direction, East of North. Start Finish N x

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Calculating Speed and Velocity These are two different quantities. Remember, speed is a scalar and velocity is a vector. speed = distance time velocity = displacement time NOTE – to find the direction of the velocity use the direction of the displacement. NOTES p.2

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TRY THIS IN PAIRS Find the distance travelled, the overall displacement, the average speed and the average velocity for a person who walks 5km, North followed by 3km, South in a time of 2 hours. 3km 5km

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TRY THIS IN PAIRS Find the distance travelled, the overall displacement, the average speed and the average velocity for a person who walks 5km, North followed by 5km, East followed by 7km, South in a time of 6 hours. 7km 5km

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A car moves 30m North, then 50m West, then 30m South in 1 minute. a)What’s the speed of the car? b)What’s the velocity of the car? Example 1 NOTES p. 2

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a) Speed = dist / t = 110 / 60 = 1.83 ms -1 3 cm = 30m 5cm = 50m 3cm = 30m 5cm = 50m Distance = 30 + 50 + 30 = 110m Displacement = 50m, West b) Velocity = disp / t = (50, West) / 60 = 0.83 ms -1, West 1cm = 10m N

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Example 2 Use a scale diagram to calculate the displacement of a man who walks 40m, North then 100m at 120 o. 4 cm = 40m 10cm = 100m 120 o x x = cm = m. = o. Displacement = m at o. 87097

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Example 3 Use Pythagoras and trigonometry to calculate the displacement of a man who walks 40m, North then 50m, East then 10m, South. 10m 50m 40m x

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50m 40 – 10 = 30m x resultant displacement magnitude (x): x 2 = 30 2 + 50 2 = 3400 x = 58.3m direction : tan = opp = 50 adj 30 = 59 o (= 059 o from North) SO…displacement = 58 m at a bearing of 059 o

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Homework for Wednesday 18 June 2014 Physics: Past Paper 1995 Q.1

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