kinematics (part 1)
DESCRIPTION
KINEMATICS (Part 1). Chp 2 Pg 19-26. 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?. Contents. Displacement vs Distance Speed vs Velocity Acceleration - PowerPoint PPT PresentationTRANSCRIPT
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KINEMATICS (PART 1)Chp 2 Pg 19-26
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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?
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CONTENTS Displacement vs Distance Speed vs Velocity Acceleration Distance-Time Graphs Speed-Time Graphs
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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”)
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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
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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
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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
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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
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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 ?)
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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
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SPEED RECORDS [NOT IN SYLLABUS] What is the speed of the fastest human? Ans: 12.42 ms-1 Usain Bolt
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SPEED RECORDS [NOT IN SYLLABUS] Speed of fastest animal on land? Ans: 29.0 ms-1
Cheetah
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SPEED RECORDS [NOT IN SYLLABUS] Speed of fastest animal in water Ans: 30.33 ms-1
Sailfish
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SPEED RECORDS [NOT IN SYLLABUS] Speed of fastest animal in air 108 ms-1
Peregrine Falcon (while diving)
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SPEED RECORDS [NOT IN SYLLABUS] Fastest car 341 ms-1
ThrustSSC First car to beat the
sound barrier
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SPEED RECORDS [NOT IN SYLLABUS] Fastest Aeroplane
SR-71 Blackbird X-151000 ms-1 2000 ms-1
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OKAY, BACK TO YOUR ACTUAL LESSON….
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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.
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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.
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TIME FOR A FIVE MINUTE TEST!=P