Title: Kinematics
1Kinematics
2Lesson 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. - .
3House
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.
4Treasure Map
5Treasure 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?
6Recall
- What is a vector?
- A vector has both magnitude and direction
- Let us look at this table below and fill in the
blanks.
7Distance and Displacement
- Distance
- A ________ quantity
- __________ only.
- Displacement
- A ______ quantity
- _________ and ___________
8Treasure Map
9Where 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.
10Where 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 ______________ ___________
___ ______________
11Where 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 , ________
-
12Distance 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 _______________
13Distance 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 ________________
14Distance 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 _______________
15Distance 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 _____________________
16Practice 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 __________________.
17Practice 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 _________________
18Speed 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
19Speed 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.
20Speed 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?
21Speed 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.
22Speed 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.
23Speed and Velocity
Question 4 Convert the following speeds between
m/s and km/h.i) 15 m/s ii) 100 km/h
24Speed 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?
25Speed 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.
26Speed 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.
27Acceleration
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.
28Acceleration
Example 1 A bus at rest is accelerated to a
velocity of 30 m/s in 10 seconds. Calculate the
acceleration of the bus.
29Acceleration
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?
30Acceleration
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.
31Acceleration
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)
32Acceleration
Question 3 A train slows down from 80 m/s to
rest in one minute. Calculate the retardation of
the train. Since ___________ is
___________ , _____________ is ___________.
33Concept map
Write down one thing you have learnt in this
lesson.
34Concept Map
All these quantities are __________________
Displacement
Velocity
They have both __________ and __________ .
Acceleration
Write down one thing you have learnt in this
lesson.