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Understanding Kinematics: Displacement, Velocity, and Acceleration in Physics

This lesson dives into the fundamentals of kinematics, exploring essential concepts such as displacement versus distance, speed versus velocity, and acceleration. Using engaging examples like Shifu and Po's travels, we differentiate between scalars and vectors, discuss distance-time and speed-time graphs, and apply these principles to real-world scenarios. Learn how to calculate average speed and velocity through practical problems and uncover fascinating records of speed in nature. This comprehensive guide lays the groundwork for understanding motion in physics.

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Understanding Kinematics: Displacement, Velocity, and Acceleration in Physics

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  1. KINEMATICS (Part 1) Chp 2 Pg 19-26

  2. What movie is this scene taken from? • Ans: X-Men First Class • What is the model of the airplane? • Ans: Lockheed SR-71 Blackbird • What’s so special about the SR-71?

  3. Contents • Displacement vs Distance • Speed vs Velocity • Acceleration • Distance-Time Graphs • Speed-Time Graphs

  4. Recall from Previous Topic • Distance is a scalar. • It is always positive in value. • Displacement is a vector • It can be either positive or negative in value • Displacement has both magnitude AND direction • The magntiude of displacement is measured from a reference point (i.e. a “zero point” or “origin”)

  5. Further Implications • One direction will be positive displacement, while the opposite direction will be negative displacement. • E.g. if going to the right is positive, going to the left is negative

  6. Example 1 • Shifu started at displacement = 0. He walks 5 metres to the right, and then walks 10 metres to the left. Take left to be the positive direction. • Qn: what is his distance travelled? • Ans: 15 m [note: ignore direction, just total everything] • Qn: what is the final displacement of Shifu? • Ans: 5 m

  7. example 2 • Po started at displacement = 0. He travels X km north on the first day. One the second day, he travelled 10 km south. If his final displacement is 6 km, what was his displacement at the end of the first day, taking South to be the positive direction? • Ans: -4 km

  8. Speed and Velocity • Also recall from previous topic: • Speed is a scalar • Velocity is a vector • In fact • Speed = Distance / Time • Velocity = Displacement / Time • Official Definitions: • Speed is the distance moved per unit Time • Velocity is the rate of change of displacement. • Unit = ms-1 • Average Speed = Total Distance / Time • Average Velocity = Final Displacement / Time

  9. Example 3 • Tai Lung ran 400 m East in 20 s, and then ran 1000 m West in 120 s. What was his (i) average speed, (ii) average velocity? • (i) Average speed = Total Distance / Time = 1400/140 = 10 ms-1 • (ii) Average velocity = Final Displacement / Time = 600 m/140 = 4.29 ms-1 (Can it be -4.29ms-1 ?)

  10. Lame Joke Alert • How do you tell apart Speed from Velocity? • Speed is an action movie starring Keanu Reeves and Sandra Bullock • Velocity is a shopping mall in Novena

  11. Speed Records [Not In Syllabus] • What is the speed of the fastest human? • Ans: 12.42 ms-1 • Usain Bolt

  12. Speed Records [Not In Syllabus] • Speed of fastest animal on land? • Ans: 29.0 ms-1 • Cheetah

  13. Speed Records [Not In Syllabus] • Speed of fastest animal in water • Ans: 30.33 ms-1 • Sailfish

  14. Speed Records [Not In Syllabus] • Speed of fastest animal in air • 108 ms-1 • Peregrine Falcon (while diving)

  15. Speed Records [Not In Syllabus] • Fastest car • 341 ms-1 • ThrustSSC • First car to beat the sound barrier

  16. Speed Records [Not In Syllabus] • Fastest Aeroplane SR-71 Blackbird X-15 1000 ms-1 2000 ms-1

  17. Okay, back to your actual lesson….

  18. Acceleration • Acceleration is defined as the rate of change of velocity with respect to time. • Formula: a = (Final Velocity – Initial Velocity)/t • Units: ms-2 • When the object’s velocity is changing with time, it is said to have an acceleration • When the object’s is changing it’s velocity at a constant rate, it is said to have uniform acceleration.

  19. Example 4 • A train initially has a velocity of 100 and it is moving towards the west. After braking for 20 s, it has a velocity of 50 . Calculate the acceleration of the train.

  20. Time for a Five Minute Test! =P

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