Form 4 Chapter 1: Introduction to Physics 1.2 Understanding Base Quantities and Derived Quantities CYS 1 Physical Quantities A physical quantity is a quanti t y that can be me asu re d . A physical quantity can be subdivided into : a) base quantity and b) derived quantity . Base Quantities Base quantities are the quantities that c annot be d e f i n e d in term of other physical quantity. Quantity Name of unit Unit symbol Length Meter m Mass Kilogr Kg Prefixes Prefixes are the preceding factor used to represent very small and very large physical quantities in SI units. Prefixes Value Standard Form Symbol Tera- 1,000,000,000,00 0 10 12 T Giga- 1,000,000,000 10 9 G Mega- 1,000,000 10 6 M Kilo- 1,000 10 3 k Deci- 0.1 10 -1 d Centi- 0.01 10 -2 c Milli- 0.001 10 -3 m Micro- 0.000 001 10 -6 Derived Quantity A derived quantity is a p h y s i cal q u a n t ity that is not a b a se quantity. It is the quantities which d e riv e d from the base quantities through m ultip l y ing and/or div i d i ng them. Example: Displacement Derived Base quantity Base Conversion of Units Examples: To convert the velocity of 20kmh -1 to ms -1 . 20 km 1 hr × 1000 m 1 km × 1 hr 3600 s = ( 20 × 1000 × 1) m ( 1 × 1 × 3600) s =5.6 ms −1
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Form 4 Chapter 1: Introduction to Physics
1.2 Understanding Base Quantities and Derived Quantities
CYS 1
Physical QuantitiesA physical quantity is a quanti t y that can be me asu re d .
A physical quantity can be subdivided into :a) base quantity and b) derived quantity .
Base QuantitiesBase quantities are the quantities that c annot be d e f i n e d in term of other physical quantity.
Quantity Name of unit
Unit symbol
Length Meter mMass Kilogram KgTime Second sElectric Current Ampere ATemperature Kelvin K
PrefixesPrefixes are the preceding factor used to represent very small and very large physical quantities in SI units.
Prefixes Value Standard Form SymbolTera- 1,000,000,000,000 1012 TGiga- 1,000,000,000 109 GMega- 1,000,000 106 MKilo- 1,000 103 kDeci- 0.1 10-1 dCenti- 0.01 10-2 cMilli- 0.001 10-3 mMicro- 0.000 001 10-6 Nano- 0.000 000 001 10-9 nPico- 0.000 000 000 001 10-12 p
Derived QuantityA derived quantity is a p h y s i cal q u a n t ity that is not a b a se quantity. It is the quantities which d e riv e d from the base quantities through m ultip l y ing and/or div i d i ng them.
Example:
Velocity=DisplacementTimeDerived quantity Base quantity
Base quantity
Conversion of UnitsExamples: To convert the velocity of 20kmh-1 to ms-1.
20km1hr
× 1000m1km
× 1hr3600 s
=(20×1000×1)m(1×1×3600)s
=5.6ms−1
Form 4 Chapter 1: Introduction to Physics
1.3 Understanding Scalar and Vector Quantities
Common Examples:LengthSpeedTimeDistanceTemperaturePowerMassEnergyWork doneDensityVolume
Common Examples:ForceAccelerationVelocityMomentumDisplacement
CYS 2
Parallax Error
1. A parallax error is an error in reading an instrument due to the eye of the observer and pointer are not in a line perpendicular to the plane of the scale.
2. Parallax error can be overcome by making sure that the position of the eye in line with the reading to be taken.
3. Parallax error can be overcome by having a mirror behind the pointer.
Zero Error
1. A zero error arises when the measuring instrument does not start from exactly zero.
2. Zero errors are consistently present in every reading of a measurement.
Form 4 Chapter 1: Introduction to Physics
Understanding Measurements
Error in Measurement
1. All measurements are value of approximation only. Therefore, it's a matter of how close the measurement is to the actual value.
2. Error is the difference between the actual value of a quantity and the value obtained in measurement.
CYS 3
Consistency / Precision
1. Consistency of a measuring instrument is its ability to register the same reading, or with only a small relative deviation between readings.
Accuracy
1. The accuracy of a measurement is how close the measurement is from the actual value.
2. The measurement is more accurate if its number of significant figures increases.
Form 4 Chapter 1: Introduction to Physics
Precision vs Accuracy
Sensitivity1. The sensitivity of an instrument is
its ability to detect small changes in the quantity that is being measured.
2. Thus, a sensitive instrument can quickly detect a small change in measurement.
3. Measuring instruments that have smaller scale parts are more sensitive.
4. Sensitive instruments need not necessarily be accurate.
CYS 4
Form 4 Chapter 1: Introduction to Physics
Measuring Instruments
Meter Ruler
The accuracy of a meter ruler is 1mm.
Vernier Caliper (Accuracy up to 0.01cm or 0.1mm)
CYS 5
Form 4 Chapter 1: Introduction to Physics
Taking reading from Vernier Caliper
Reading of Vernier Caliper= Reading of Main Scale + Reading of Vernier Scale= 1.1 + 0.07= 1.17cm
CYS 6
Form 4 Chapter 1: Introduction to Physics
Zero Error for Vernier Caliper
The zero error is determined by tightening the jaws of the vernier calipers.
Positive Zero Error (+0.02cm)
Negative Zero Error (-0.04cm)
Micrometer Screw Gauge (Accuracy up to 0.001cm or 0.01mm)
CYS 7
Form 4 Chapter 1: Introduction to Physics
Taking reading from Micrometer Screw Gauge
Reading of Micrometer Screw Gauge= Main Scale (Sleeve)+ Thimble Scale
= 5mm+0.07mm= 5.07mm
= 5.5mm + 0.07mm= 5.57mm
CYS 8
Form 4 Chapter 1: Introduction to Physics
Zero Error for Micrometer Screw Gauge
Positive Zero Error (+0.03mm)
Negative Zero Error (-0.03mm)
CYS 9
Form 4 Chapter 1: Introduction to Physics
Analyzing Graph
P increase linearly with Q P decrease linearly with Q
P is directly proportional to Q P is inversely proportional to Q
CYS 10
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