Download - physics Linear Motion
-
8/7/2019 physics Linear Motion
1/41
-
8/7/2019 physics Linear Motion
2/41
CHAPTER 2
FORCES AND MOTION
2.1 Analysing Linear Motion
Expected learning outcomes
Student should be able to :
1. define distance and displacement
2. define speed and velocity
3. define acceleration and deceleration
4. calculate speed and velocity
5. calculate acceleration/deceleration
6. solve problems on linear motion with uniform acceleration using :
(i) v = u + at
(ii) s = ut + at2
(iii) v2= 2as
-
8/7/2019 physics Linear Motion
3/41
-
8/7/2019 physics Linear Motion
4/41
Distance and Displacement
1. Distance is the total path length travelled from one location toanother. It is a scalarquantity.The SI Unit is meter (m)
2.Displacement is the distance between two locations measured
along the shortest path connecting them, in a specified direction.
It is a vector quantity. The SI Unit is meter(m)
-
8/7/2019 physics Linear Motion
5/41
2m 2 m Distance = 4 m
Displacement = 4 m
3m1 m
Distance = 3 + 1 +1 = 5m
Displacement = 3m + 1+ ( -1) =3 m toright
A B
AC
B
A B C
-
8/7/2019 physics Linear Motion
6/41
-
8/7/2019 physics Linear Motion
7/41
-
8/7/2019 physics Linear Motion
8/41
-
8/7/2019 physics Linear Motion
9/41
Exercise 1:
1. What is the distance he had to drive to reach his school?
2. What is the displacement of the school from the house?
3. What is the total distance he had to drive to reach back to
his house?
4. What is the total displacement he drove back to his
house?
-
8/7/2019 physics Linear Motion
10/41
Speed and Velocity
Speed is the distance travelled per unit time or the rate of change ofdistance.
Average speed, v= Total distance travelled, s (m) SI unit = m/s
Time taken, t(s)
Velocity is the speed in a given direction or the rate of change ofdisplacement.
Average velocity, v=Displacement, s (m)
Time taken, t(s)
-
8/7/2019 physics Linear Motion
11/41
-
8/7/2019 physics Linear Motion
12/41
-
8/7/2019 physics Linear Motion
13/41
Q1 : If the time taken by Ahmad to travel from his house to school
is 15 minutes, what is his speed and velocity?
-
8/7/2019 physics Linear Motion
14/41
Positive velocity
Displacement : Right directionDisplacement left direction
Negative velocity
-
8/7/2019 physics Linear Motion
15/41
Acceleration and Deceleration1. Acceleration is defined as the rate of change of velocity.
Acceleration = Change of velocity
Time taken
= Final velocity Initial velocity
Time taken
a = vu
t
The acceleration of an object is a vector quantity. The SI units for speed
is ms-2
Negative acceleration is known as deceleration. If the velocity of an
object is remain constant, the object is said to move with zero
acceleration.
If the rate of change of its velocity is constant, the object move uniformacceleration or zero acceleration.
-
8/7/2019 physics Linear Motion
16/41
-
8/7/2019 physics Linear Motion
17/41
Acceleration, a = vu
t
A runner accelerates at a constant rate from rest and reaches a
velocity of 10 ms-1 after 5.0s. What is his acceleration?
Initial velocity, u = 0
Final velocity, v = 10ms-1
Time interval, t = 5.0s= 10 - 0
5= 2 ms-2
1. Calculate its average acceleration.
2. A motorcycle, travelling at 40.0 ms-1, takes
10s to stop. What is its average deceleration?
-
8/7/2019 physics Linear Motion
18/41
A car decrease its velocity from 108 kmh-1 to 72 kmh-1 in 5 s. What is the
deceleration of the car ?
Solution :
-
8/7/2019 physics Linear Motion
19/41
Next Click
>play
-
8/7/2019 physics Linear Motion
20/41
The time taken to make 50 dots on the ticker tape is 1s. Hence , the
time interval between 2 consecutive dots (tick) is 1/50 = 0.02s.
-
8/7/2019 physics Linear Motion
21/41
tick
Strip
5 tick strip
tick tick tick tick
1 2 3 4 5
A tape chart
-
8/7/2019 physics Linear Motion
22/41
Direction of the movement of ticker tape
Direction of the movement of ticker tape
v
t
-
8/7/2019 physics Linear Motion
23/41
Direction of the movement of the ticker tape
v
t
-
8/7/2019 physics Linear Motion
24/41
v
t
Direction of the movement of the ticker tape
-
8/7/2019 physics Linear Motion
25/41
To determine the velocity of a ticker tape
30.0 cm
Velocity = Displacement
Time taken
v = s
t
s = 30
7x
0.02
V =
214.28m/s
-
8/7/2019 physics Linear Motion
26/41
To determine the velocity of strips of ticker tape
velocity
v = s
t
v = 8+6+9+8+10
1.0
v = 41.0 cms-1
-
8/7/2019 physics Linear Motion
27/41
-
8/7/2019 physics Linear Motion
28/41
To determine acceleration from the ticker tape
=833.33cm/s
-
8/7/2019 physics Linear Motion
29/41
Ticker tape chart
Length/cm
time
Physics is fun
We can determine
velocity,
acceleration,time
taken and
acceleration from
ticker tape chart!!!
-
8/7/2019 physics Linear Motion
30/41
-
8/7/2019 physics Linear Motion
31/41
-
8/7/2019 physics Linear Motion
32/41
-
8/7/2019 physics Linear Motion
33/41
-
8/7/2019 physics Linear Motion
34/41
-
8/7/2019 physics Linear Motion
35/41
The Equation of Motion
s = Displacementu= Initial velocity
v= Final velocity
a = Constant acceleration
t= Time interval
V = u+ ats= ut+ at2
v2 = u2 + 2as
V = s/t
s = u+ v t
2
-
8/7/2019 physics Linear Motion
36/41
Hazuri is driving a car at a velocity of 30 ms-1. On seeing a student
crossing the road, Hazuri steps on his brakes to stop the car. The
speed of the car decreases uniformly and comes to a halt after
travelling 150m.a) What is the deceleration of the car when the brakes are applied.
b) What is the time interval before the car stops.
-
8/7/2019 physics Linear Motion
37/41
Try your understanding!!
1. Jerry rides his bicycle starting from restand accelerates at a uniform rate of0.5ms-2. What is the time taken to travel a
distance of 100m? 2. The velocity of a car, decelerating
uniformly, decreases from 10ms to 6 ms.The distance travelled in the period ofdeceleration is 16m. What is the additionaldistance travelled before the car stops?
-1 -1
-
8/7/2019 physics Linear Motion
38/41
Check your answer
1. s = ut + a t
100 = 0 + (0.5) t2
t = 400 s
t = 20 s
2. v =u + 2 as
62=102 + 2 a (16)
a =- 2 ms
Whenthe bicyclestops,v= 0
U = 6 ms v = 0 ms-2
v2=u2 + 2 as 02=62 + 2 (-2) s
4s=36
.s =9 m
Good try!!
2
2
2 2
-2
-
8/7/2019 physics Linear Motion
39/41
Right hand>.play
-
8/7/2019 physics Linear Motion
40/41
Right hand>.play
-
8/7/2019 physics Linear Motion
41/41
Right hand>.play