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Chapter 1: Physical Quantities, Units and Measurements
Many things around us move in a manner thatrepeats itself.
Eg. Stand fan which switched on, air -conditioner outlets, frequency of the bus 972,etc.
In science, it is more convenient to use thependulum to study this repeated motion.
A simple pendulum consists of a bob (smallweight) swinging back and forth on a string.
A full oscillation occurs when there is acomplete to and fro motion of the bobfrom A➜B➜C➜B➜A.
It is defined as the time taken for one full fulloscillation to occur.
It is defined as the number of completeoscillation in 1 second.
Ticker tape timer
A ticker tape timer is an electrically operateddevice that marks very short intervals of timeonto a tape in the form of dots.
The time is connected to an electricity supplyand cause the metal strip attached to thetimer to vibrate. Eg: 50 Hz or 50 times everysecond.
The time interval between two consecutive dotsis 1/50 s = 0.02s.
Frequency of Ticker Tape: No of dots producedin a second.
Hence, the ticker tape timer is a kind of clockthat measures time in 0.02s intervals.
When distance between successive dots isconstant, the tape is moving at a constantspeed.
When distance between successive dotsincreases, the tape is moving faster (speedincrease).
When distance between successive dotsdecreases, the tape is moving slower (speeddecreases).
Measurement Of Time
SI Unit: Second
Degree of Accuracy: 1 Second
Degree of Accuracy: 0.01 second (Digital), 0.1second (Analog)
Degree of Accuracy: 0.02 seconds between 2dots
Measurement of Length
SI Unit: Metres
* The type of instrument used to measurelength depends on the length to be measuredand the accuracy required. Accuracy is thesmallest unit an instrument can measure.
Measured Length Range: 0m 10m
Accuracy: 0.1cm or 1 mm
Measured Length Range: 0cm to 100cm
Accuracy: 0.1 to 1 mm
Measured Length Range: 2cm to 10cm or20mm to 100mm
Accuracy: 0.01cm or 0.1mm
Micrometer Screw Gauge
Measured Length Range: Less than 3 cm or0mm to 30mm
Accuracy: 0.001cm or 0.01mm
Accuracy: 0.1cm or 1mm
The incorrect way of reading from a ruler leadsto it
How to prevent it?
When taking the measurement on a ruler. placethe eye directly above the scale.
Take several readings, and then take theaverage.
+More on Vernier Caliper
Before any measurement is made, there isalready some measurement MORE.
Solution: Minus this error to the reading.
Before any measurement is made, there isalready some measurement LESS.
Solution: Add this error to the reading
+ More on Micrometer Screw Gauge
When reading a Micrometer Screw Gauge, errorcan occur due to zero error.
Thus before we use the instrument, we mustcheck for zero error.
The zero marking on the thimble scale is belowthe datum line.
The zero marking on the thimble scale is abovethe datum line.
They are used to express physical quantitiesthat are either very large or very small.
Prefixes are based on the SI unit of theparticular physical quantity.
Derived Quantities and their SI Units
They are quantities derived from two or morebase physical quantities
Length × Width
Length × Width × Height
Mass ÷ Volume
kg/m³ or kgm-³
Distance ÷ Time
m÷s or ms-²
Mass × Acceleration
kg m s-²
Base Quantitiesand their SI Units
SI stands for&quot;International Systemof Units&quot;
SI Unit: Metre
SI Unit: Kilogram
SI Unit: Seconds
SI Unit: Ampere
SI Unit: Kelvin
Amount of Substance
SI Unit: Mole
SI Unit: Candela
They are quantities that can be measured andthey consist of a numerical magnitude/numberand a unit.