chapter-1-physical-quantities-units-and-measurements

Chapter 1: Physical Quantities, Units and Measurements
Periodic Motion
Many things around us move in a manner that
repeats itself.
Eg. Stand fan which switched on, air -
conditioner outlets, frequency of the bus 972,
etc.
In science, it is more convenient to use the
pendulum to study this repeated motion.
Pendulum
A simple pendulum consists of a bob (small
weight) swinging back and forth on a string.
Oscillation
A full oscillation occurs when there is a
complete to and fro motion of the bob
from A➜B➜C➜B➜A.
Period
It is defined as the time taken for one full full
oscillation to occur.
Frequency
It is defined as the number of complete
oscillation in 1 second.
Ticker tape timer
A ticker tape timer is an electrically operated
device that marks very short intervals of time
onto a tape in the form of dots.
The time is connected to an electricity supply
and cause the metal strip attached to the
timer to vibrate. Eg: 50 Hz or 50 times every
second.
The time interval between two consecutive dots
is 1/50 s = 0.02s.
Frequency of Ticker Tape: No of dots produced
in a second.
Hence, the ticker tape timer is a kind of clock
that measures time in 0.02s intervals.
When distance between successive dots is
constant, the tape is moving at a constant
speed.
When distance between successive dots
increases, the tape is moving faster (speed
increase).
When distance between successive dots
decreases, the tape is moving slower (speed
decreases).
Measurement Of Time
SI Unit: Second
Symbol: s
Instruments Used:
Clocks
Degree of Accuracy: 1 Second
Stopwatches
Degree of Accuracy: 0.01 second (Digital), 0.1
second (Analog)
Ticker-tape Timer
Degree of Accuracy: 0.02 seconds between 2
dots
Measurement of Length
SI Unit: Metres
Symbol: m
* The type of instrument used to measure
length depends on the length to be measured
and the accuracy required. Accuracy is the
smallest unit an instrument can measure.
Instruments
Measuring Tape
Measured Length Range: 0m 10m
Accuracy: 0.1cm or 1 mm
Metre Rule
Measured Length Range: 0cm to 100cm
Accuracy: 0.1 to 1 mm
Vernier Calipers
Measured Length Range: 2cm to 10cm or
20mm to 100mm
Accuracy: 0.01cm or 0.1mm
Micrometer Screw Gauge
Measured Length Range: Less than 3 cm or
0mm to 30mm
Accuracy: 0.001cm or 0.01mm
Rulers
Accuracy: 0.1cm or 1mm
Parallax Error
The incorrect way of reading from a ruler leads
to it
How to prevent it?
When taking the measurement on a ruler. place
the eye directly above the scale.
Take several readings, and then take the
average.
+More on Vernier Caliper
Zero Errors
Positive
Before any measurement is made, there is
already some measurement MORE.
Solution: Minus this error to the reading.
Negative
Before any measurement is made, there is
already some measurement LESS.
Solution: Add this error to the reading
+ More on Micrometer Screw Gauge
Zero Errors
When reading a Micrometer Screw Gauge, error
can occur due to zero error.
Thus before we use the instrument, we must
check for zero error.
Positive
The zero marking on the thimble scale is below
the datum line.
Negative
The zero marking on the thimble scale is above
the datum line.
Prefixes
They are used to express physical quantities
that are either very large or very small.
Prefixes are based on the SI unit of the
particular physical quantity.
Giga
Symbol: G
10^9
Mega
Symbol: M
10 ^6
Kilo
Symbol: k
10^3
Deci
Symbol: d
10^-1
Centi
Symbol: c
10^-2
Milli
Symbol: m
10^-3
Micro
Symbol: μ
10^-6
Nano
Symbol: n
10^-9
Derived Quantities and their SI Units
They are quantities derived from two or more
base physical quantities
Area
Length × Width
m ²
Volume
Length × Width × Height
Density
Mass ÷ Volume
kg/m³ or kgm-³
Speed
Distance ÷ Time
m÷s or ms-²
Force
Mass × Acceleration
kg m s-²
Base Quantities
and their SI Units
SI stands for
"International System
of Units"
Length
SI Unit: Metre
Symbol: m
Mass
SI Unit: Kilogram
Symbol: kg
Time
SI Unit: Seconds
Symbol: s
Electrical Current
SI Unit: Ampere
Symbol: A
Temperature
SI Unit: Kelvin
Symbol: K
Amount of Substance
SI Unit: Mole
Symbol: mol
Luminous Intensity
SI Unit: Candela
Symbol: cd
Physical Quantities
They are quantities that can be measured and
they consist of a numerical magnitude/number
and a unit.
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