Kinematics

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Kinematics
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Lesson Objectives
Lesson Objectives

• At the end of lesson, students should be able to
• State what is meant by distance and displacement.
• State what is meant by speed and velocity, and
  calculate average speed and velocity.
• State what is meant by uniform acceleration, and
  calculate acceleration.
• .

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House
You are visiting a friend on his island. One day,
he shows you a map of the island. At the bottom
of the map there is this message. Dig 3km away
from the house for the treasure. Both of you
decide to set off to find this treasure.
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Treasure Map
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Treasure Map

• Where do you start to dig for the treasure?
• Is there enough information to know where to dig?
• What other information do we need?

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Recall

• What is a vector?
• A vector has both magnitude and direction
• Let us look at this table below and fill in the
  blanks.

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Distance and Displacement

• Distance
• A ________ quantity
• __________ only.
• Displacement
• A ______ quantity
• _________ and ___________

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Treasure Map
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Where to dig?

• We decide to dig at the hills for the treasure.
  We walk along path A and D from the house. The
  total distance we have traveled is 1.5km 1.5km
  3km.

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Where to dig?

• However, our displacement is not 3 km.
• Our displacement is shown by the direct line (in
  red)

Displacement Calculation Let displacement be
s By Pythagoras Theorem ______________ ___________
___ ______________
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Where to dig?

• Instead of walking to the hills, we decide to dig
  at the rock. We start from the house and then
  walk west for 3km to reach the rock and we dig
  there.
• What is our distance traveled?
• Distance traveled ______ km
• What is our displacement?
• Displacement ______km , ________

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Distance and displacement

• Question 1
• Starting from the house,
• We walk along path B, path G and path H. What is
  our (i) Distance traveled. (ii) Displacement.
• (i) Distance traveled ____________
• (ii) Displacement _______________

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Distance and displacement

• Question 2
• Starting from the house,
• We walk along path C, path I and path J. What is
  our (i) Distance traveled. (ii) Displacement.
• (i) Distance traveled _____________
• (ii) Displacement ________________

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Distance and displacement

• Question 3
• Starting from the house,
• We walk along path B. What is our
• (i) Distance traveled. (ii) Displacement.
• (i) Distance traveled ____________
• (ii) Displacement _______________

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Distance and displacement

• Question 4
• Starting from the house,
• We walk along path A, path D, path E, Path F,
  and path B. What is our
• (i) Distance traveled. (ii) Displacement.
• (i) Distance traveled __________________
• (ii) Displacement _____________________

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Practice Question 1

• The diagram below shows position of a
  cross-country skier at various times. The skier
  moves from A to B to C to D. Determine the
  distance traveled by the skier and the resulting
  displacement during these three minutes.

Distance Traveled ___________________ Total
Displacement __________________.
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Practice Question 2

• Diagram below shows several of Beckhams
  positions at various times of a football game.
  Beckham moves from position A to B to C to D.
  What is Beckham's resulting displacement and
  distance traveled?

Distance Traveled __________________ Total
Displacement _________________
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Speed and Velocity
Speed Definition Speed is defined as the rate of
change of distance with time.
Equation ________ where v speed
s distance t time interval
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Speed and Velocity
Example A motorcycle covers a distance of 15 km
in 30 minutes. Q. What is the motorcycles
average speed?     Q. Does the average speed
help us to determine the maximum or minimum speed
of the motorcycle?    Q. The above answer seems
slow for a motorcycle. Explain why it is
probably correct.
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Speed and Velocity
Question 1 A plane travels at a constant speed
and covers a distance of 2750 km in a period of 2
hours 30 minutes. What is the speed of the
aeroplane?
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Speed and Velocity
Question 2 A man walks along his garden path
in 2 mins. If his average speed for the walk was
2 m/s, how long is his garden path?
Note the SI units of speed and time in this
example.
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Speed and Velocity
Question 3 A man jogs a distance of 8 km in 40
minutes. Calculate his average speed in (i)
km/h (ii) m/s.

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Speed and Velocity
Question 4 Convert the following speeds between
m/s and km/h.i) 15 m/s ii) 100 km/h
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Speed and Velocity
Question 5You walk a distance of 2 km at an
average speed of 8 km/h. You then run for a
further 5 minutes with an average speed of 14
km/h. What is your average velocity for the
whole journey?
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Speed and Velocity
Velocity Velocity is a vector and has both
magnitude and direction.. Definition Velocity
is defined as the rate of change of distance in a
specified direction

with
time.Velocity can also be defined as the rate
of change of displacement with time.
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Speed and Velocity
Example A car drives 40 km north along a road
and then 20km south along the same road. It takes
2 hours to complete its journey. Calculate a)
average speed for the journey b) the average
velocity for the journey.
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Acceleration
Acceleration is defined as the rate of change of
velocity with respect to time. Equation

_______________________ where a acceleration
in m s-2 v final velocity in m s-1
u initial velocity in m s-1
t time interval between the change from
the initial velocity to the final velocity.
 
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Acceleration
Example 1 A bus at rest is accelerated to a
velocity of 30 m/s in 10 seconds. Calculate the
acceleration of the bus.
 
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Acceleration
Question 1 A car is travelling at a constant
velocity of 20 m/s before it accelerates to a
velocity of 65 m/s in 5 seconds. What is the
acceleration of the car?
 
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Acceleration
Question 2 A car initially has a velocity of 60
m/s. After braking for 5 seconds it has a
velocity of 20 m/s. Calculate the acceleration of
the car.
 
Note the negative sign for the acceleration in
this case.
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Acceleration
Deceleration When an object reduces its velocity
(or speed), we can state this in several
way.   We can say that the object (a) (b) (c)
 
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Acceleration
Question 3 A train slows down from 80 m/s to
rest in one minute. Calculate the retardation of
the train. Since ___________ is
___________ , _____________ is ___________.
 
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Concept map
Write down one thing you have learnt in this
lesson.
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Concept Map
All these quantities are __________________
Displacement


Velocity
They have both __________ and __________ .


Acceleration
Write down one thing you have learnt in this
lesson.