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
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 Distance-Time Graphs Speed-Time Graphs
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”)
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
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
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
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
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 ?)
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
SPEED RECORDS [NOT IN SYLLABUS] What is the speed of the fastest human? Ans: 12.42 ms-1 Usain Bolt
SPEED RECORDS [NOT IN SYLLABUS] Speed of fastest animal on land? Ans: 29.0 ms-1
Cheetah
SPEED RECORDS [NOT IN SYLLABUS] Speed of fastest animal in water Ans: 30.33 ms-1
Sailfish
SPEED RECORDS [NOT IN SYLLABUS] Speed of fastest animal in air 108 ms-1
Peregrine Falcon (while diving)
SPEED RECORDS [NOT IN SYLLABUS] Fastest car 341 ms-1
ThrustSSC First car to beat the
sound barrier
SPEED RECORDS [NOT IN SYLLABUS] Fastest Aeroplane
SR-71 Blackbird X-151000 ms-1 2000 ms-1
OKAY, BACK TO YOUR ACTUAL LESSON….
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.
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.
TIME FOR A FIVE MINUTE TEST!=P