Unit 1
GENERAL PHYICS
1.1 Measurements and motion
Basic Quantities & Units
Unit conversion:
SI Unit System:
x100
x1000
#
Quantity SI Unit
Kilogram
Mass
Symbol
kg
Metre
Length
Km
Second
s
Force
Newton
N
Current
Ampere
A
Km ²
2- Convert 8cm to
km
3-convert 6 hours
to seconds
m²
cm ²
÷1000 ²
÷100 ²
x60
x60
Hour
1-Convert 2.5 km to
metre
÷10
x100 ²
x1000 ²
Question
mm
cm
÷100
÷1000
m
Time
m
Measuring techniques
x10
Min
Measure
Using
Length
Ruler/Tape
Mass
Electronic scale
Time
Stopwatch/Clock
Temperature
Thermometre
Thickness
Vernier caliper /
Micrometer
+
Sec
÷60
÷60
Thermometre
Vernier caliper
Stopwatch
K
Kilo
x1000
c
Centi
÷100
m
Milli
÷1000
Micrometer
Spring balance
Electronic scale
Length
Can be measured using…
Metre rule
Measuring tape
Can measure up to 1 m
Can measure up to 10 m
The smallest scale is 1 mm
The smallest scale is 1 mm
They are often hard
They are often flexible and soft
Used in precise
measuring and drafting
Used to measure long
distances and cur ved paths
Measure thickness of a sheet of paper
Measuring a thickness of a sheet may seem impossible
So
We measured the thickness of a set of similar sheets
Together and divide it by the number of sheets
Measure circumference of a cylinder
We measured the circumference of a cylinder, by
measuring the diameter and calculating the
circumference
Or
by wrapping a thread around the cylinder and
measuring the whole thread length, and divide by
the number of cycles to get single cycle length.
Errors
Zero error
Zero error is an error where the starting
point in the measurement is not zero
This can happen due to non-calibrated
apparatus
Parallax error
Parallax error is an error when the apparatus
position of An object differs when viewed from
different angles
So you always need to look perpendicular to the
apparatus in order to avoid parallax error
How to minimize the effect of errors….?
But repeating and taking an average
A table heights was measured and 5 different readings where taken
10.4 - 10.2 - 9.9 - 10.1 - 10.3
We take an average for the readings
10.1
So the percentage of error decreases as the average is taken and the accuracy increases
Significant figures
Significant figures of the digits in a value that contributes to its accuracy
Any number counts as a significant figure, but zeros
Significant figure isn’t decimal place
&
Before a number
Doesn’t count as a
significant figure
EX:
02
005
0.04
Bet ween numbers
Counts as a
significant figure
Ex:
104
5054
9801 \. 40.45
After a number
If there is decimal point it counts a
significant figure
If to the left of a number, it doesn’t count
as a significant figure
Ex
320 (zero is no s.f) 2sf
650.0 (zero is sf) 4sf
Scalar and Vector quantities
VECTOR
SCALAR
-
Definition: They are the quantities that is defined using
magnitude only (size or amount ) and doesn’t include any
direction
Definition: They are the quantities that is defined using
magnitude and direction
Ex. Temperature , if you say that the temperature is 25°C
you’re providing a scalar quantity, because it only tells us
how hot or cold It is without any direction associated
with it.
Ex. Velocity, if you say a car is moving at 60 km/h,
north, you’re providing a vector quantity because it tells
us both how fast the car is going (magnitude=60km/h)
and the direction in which it’s moving (north)
Known scalar quantities:
Known vector quantities:
Mass
Force
Time
Acceleration
Distance
Displacement
Speed
Moment
Work
Weight
Energy and Power
Momentum
Distance and Displacement
Speed and Velocity
Mass and Weight
• Distance is the total length of
the path traveled by an object
from its initial position to its
final position
• Speed is the distance traveled
per time OR rate of change in
distance
• Mass is the amount of
matter in the object
property of an object that
resist change in motion
and is measured in KG
While
While
• Displacement is the direct
length bet ween t wo points
measured along the shortest
path connecting them. (It’s
always a straight line)
https://youtu.be/-EfxiGUucUk?si=lFNK6T5qMLL1q_wX
•Velocity is the displacement per
unit time OR rate of change in
displacement
• So the magnitude of velocity is
the speed
3
↑
-
• Weight is gravitational
force that pulls the object
downwards and depends on
the mass, its unit is
Newtons (N)
Weight = Mass x g
So mass can never changes but
weight changes as the G changes
10 m
&
10 m
&
&
3m
What is the total distance and displacement from A to C
Vector Diagram
Scale Diagram
-
Triangle Method
Mathematical Method
Step 1: Set a scale
Step 2: Draw the first vector
Pythagoras theorem
2
Step 3: Draw the second vector from the point the
first vector ended
(so they are head to tail)
Step 4: Draw an arrow from the point the first vector
started to the point the second vector ended to
complete a triangle (This is the resultant vector)
2
2
C=B+A
TAN (angle) = opposite
adjacent
-
NOTE!!
-
You can use the scale
diagram with any
vector quantity
(
Density
Density: ( ῥ)
It is the mass per unit
volume
If we say water density is 1000kg/cm ³
Then 1 cm dimension cube of
water weights 1000kg!!!!!
m
Mass
=
I
V
Volume
Unit : kg/m³
g/cm ³
NOTE
When t wo liquids are mixed
the less dense liquid float on
the surface, and the more
dense liquid sinks to the
bottom
M
V
Kg
Cm³
Kg/cm ³
Question
M
V
g
Cm³
g/cm ³
Calculate the density
of a 2cm radius
sphere with mass of
1.5kg?
M
V
Kg
m³
Kg/m ³
M
V
g
m³
g/m ³
Hint:v=4/3 pi r ³
Solids
Particles of solids are tightly
packed
Il
Particles of liquids are loosely
packed
Their shapes are not fixed
Shapes: fixed
Volume: fixed
They are highly rigid
Strong forces of attraction/
intermolecular forces are
present between solid
particles
Motion: Vibrations
They are not easily
compressible materials
Force: very strong
Kinetic energy of solid
particles is very low for
which they only vibrate
they cannot flow
Gases
Liquids
Particles of gases are free
to move
Shapes of gases are not
and depend on the medium
(Container shape)
container
Liquids have fixed volume as
Gases do not have fixed volume
well
They are less rigid
fixed and take the space of
They are not rigid at all
Intermediate force of attraction/ Comparatively very weak forces/
intermolecular forces are present intermolecular forces of attraction
between liquids
Slide over each other
These materials can be
compressed slightly
Strong
Kinetic energy of liquid
particles is intermediate
between gases and solids
They can flow
are present in gases
rapid and random
They are the most
compressible ones
Very weak
Kinetic energy of gases is
very high for which they attain
a random motion
They can flow
Which is heavier….?
I=
m
V
Using a scale
or balance
-Mass
Volume
&
Unit :m³
Regular
÷1000 ³
By measuring cylinder
cm ³
m³
Km ³
By calculating the volume
of a shape By ruler
x100 ³
x1000 ³
Irregular
÷100 ³
NOTE!!
Always take
reading from
bottom of meniscus
W
V2 - V1
=
volume of object
Which is more dense..???
Pool full of water
Glass full of water
·
Both are the SAME DENSITY !!!!!!!!!
As same substances have the same density.
Which is more dense..???
Steel Block
Wooden block
-
Due to different densities of different matters,
Low density substances float on greater density substances
Alcohol density is less than oil and water
Oil density is less than water but more than alcohol
Water density is more than both alcohol and oils
Lowest density
Desnity less than water
and more than alcohol
Highest density
Motion
Distance time graph
Motion
Distance & Speed time graph
-
In this lesson, we are going to represent the motion of an object on a graph so
first we need to know how to deal with a graph
Slope
Slope or gradient is a property that shows how steep a line is (compared to the X axis).
In physics, we use it to represent the rate of change bet ween t wo points on a line
S=
=
Y2 - Y1
X2- X 1
2-1
(0,2)
(-4,1)
0-(-4)
S=
1
4
&
Get the slope of this graph
Distance-time graph
• Distance-time graph represents distance traveled by the object as
time passes.
Distance is on the Y axis
-
Time is on the X axis
2
Slope = Y = Distance = Speed / Velocity
.
X
1
Time
&
So the slope of any distance-time
graph represents speed/velocity
Average speed = Total distance covered
https://youtu.be/tSnT_UjKvyE?si=GDAHzFqvhISjaG6y l
Total time covered
#
-
Slope = speed
Slope = Zero
AT REST
Shows that there is a
constant change in
distance as time
passes Slope = const
Shows that there’s
no change in
distance as time
passes
Slope = speed
Speed is constant
Speed= zero
Slope = speed
Slope = zero
Acceleration = zero
Shows that there is
an non-uniform
increase in distance
as time passes
Shows that there is
a non-uniform
increase in distance
as time passes
Increasing speed
Decreasing speed
Acceleration
Slope = speed
Slope = inc.
Deceleration
Slope = speed
Slope = Dec.
Velocity-time graph
Speed-time graph
Velocity time graph represents the velocity of the object as time passes
Slope = Δy = Δv
Velocity on Y axis
Time on X axis
Slope = Y = Δ Velocity =Acceleration
X
Δ time
Area under the graph = Y x X =velocity x time = total distance
Δx
#
Δt
=Acc
Calculate total distance traveled
and the acceleration in the first
t wo seconds
Acceleration = V - U
t
Avg. velocity= V+U
2
I
slope-zero
Slope
=
azo
ACC
a= 0
a= 0
azuslope oa
-of
Cast v
v= o
-
-
Stationary
4
-
a
I
3
D
·
F
2
Moving with constant speed
Acc. = zero
-
Increasing speed
Speed increases
Increasing acceleration
Decreasing acceleration
Speed increases
Constant acceleration.
g
slope As
=
des Slope
7
=
Dec
Speed decreases
Deceleration , -ve acceleration
Acceleration
Acceleration is the rate of change in velocity.
Acceleration = V - U
t
+ ve acc.
speed
·
-ve acc.
Speed
&
0
0
10
10
1
5
30
2
0
Acceleration
Acceleration
o
Also Acceleration…!!!!
But negative
/il
Increasing acceleration
Decreasing acceleration
Constant acceleration
3 Yachts moves along a road and its velocity is recorded below each second
0
0
+10
10
30
60
110
+20
+30
+50
+10
10
14
0
5
+4
17
+3
19
+2
+5
+5
10
15
20
+5
+5
Area under the graph
Calculate the area under the graph
• The area enclosed by the graph and the t wo axis
• It can have many shapes :
triangle
trapezium Or combination of them
rectangle
1
+
1
1 (4) (8) + (6)(8)
2
16 + 48
= 64 meters
So we calculate the area
under the graph by
calculating the area of
shape formed by the graph